Control of Air Pollution From New Motor Vehicles: Proposed Heavy- Duty Engine and Vehicle Standards and Highway Diesel Fuel Sulfur Control Requirements

[Federal Register: June 2, 2000 (Volume 65, Number 107)]
[Proposed Rules]
[Page 35429-35478]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr02jn00-26]

[[Page 35429]]

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Part II

Environmental Protection Agency

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40 CFR Parts 69, 80, and 86

Control of Air Pollution From New Motor Vehicles: Heavy-Duty Engine and
Vehicle Standards; Highway Diesel Fuel Sulfur Control Requirements;
Proposed Rules

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Parts 69, 80, and 86

[AMS-FRL-6705-2]
RIN 2060-AL69

Control of Air Pollution From New Motor Vehicles: Proposed Heavy-
Duty Engine and Vehicle Standards and Highway Diesel Fuel Sulfur
Control Requirements

AGENCY: Environmental Protection Agency.

ACTION: Notice of proposed rulemaking.

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SUMMARY: Diesel engines contribute considerable pollution to our
nation's continuing air quality problems. Even with more stringent
heavy-duty highway engine standards set to take effect in 2004, these
engines will continue to emit large amounts of nitrogen oxides and
particulate matter, both of which contribute to serious public health
problems in the United States. These problems include premature
mortality, aggravation of respiratory and cardiovascular disease,
aggravation of existing asthma, acute respiratory symptoms, chronic
bronchitis, and decreased lung function. Numerous studies also link
diesel exhaust to increased incidence of lung cancer.
The diesel engine is a vital workhorse in the United States, moving
much of the nation's freight, and carrying out much of its farm,
construction, and other labor. Diesel engine sales have grown over the
last decade, so that now about a million new diesel engines are put to
work in the U.S. every year. Diesels overwhelmingly dominate the bus
and large truck markets and have been capturing a growing share of the
light heavy-duty vehicle market over the last decade.
We are proposing a comprehensive national control program that
would regulate the heavy-duty vehicle and its fuel as a single system.
We are proposing new emission standards that would begin to take effect
in 2007, and would apply to heavy-duty highway engines and vehicles.
These proposed standards are based on the use of high-efficiency
catalytic exhaust emission control devices or comparably effective
advanced technologies. Because these devices are damaged by sulfur, we
are also proposing to reduce the level of sulfur in highway diesel fuel
significantly by the middle of 2006.
Diesel engines are more durable and get better fuel economy than
gasoline engines, but also pollute significantly more. If this program
is implemented as proposed, diesel trucks and buses will have
dramatically reduced emission levels. This proposed program will bring
heavy-duty diesel emissions on par with new cars. The results of this
historic proposal would be comparable to the advent of the catalytic
converter on cars, as the proposed standards would, for the first time,
result in the widespread introduction of exhaust emission control
devices on diesel engines.
By 2007, we estimate that heavy-duty trucks and buses will account
for as much as 30 percent of nitrogen oxides emissions from
transportation sources and 14 percent of particulate matter emissions.
In some urban areas, the contribution will be even greater. The
standards for heavy-duty vehicles proposed in this rule would have a
substantial impact on the mobile source inventories of oxides of
nitrogen and particulate matter. Beginning the program in the 2007
model year ensures that emission reductions start early enough to
counter the upward trend in heavy-duty vehicle emissions that would
otherwise occur because of the increasing number of vehicle miles
traveled each year.
This proposed program would result in particulate matter and oxides
of nitrogen emission levels that are 90% and 95% below current
standards levels, respectively. In order to meet these more stringent
standards for diesel engines, the proposal calls for a 97% reduction in
the sulfur content of diesel fuel. As a result, diesel vehicles would
achieve gasoline-like exhaust emission levels, in addition to their
inherent advantages over gasoline vehicles with respect to fuel
economy, lower greenhouse gas emissions, and lower evaporative
hydrocarbon emissions. We are also proposing more stringent standards
for heavy-duty gasoline vehicles.
The clean air impact of this program would be dramatic when fully
implemented. By 2030, this program would reduce annual emissions of
nitrogen oxides, nonmethane hydrocarbons, and particulate matter by a
projected 2.8 million, 305,000 and 110,000 tons, respectively. We
project that these reductions and the resulting significant
environmental benefits of this program would come at an average cost
increase of about $1,700 to $2,800 per new vehicle in the near term and
about $1000 to $1600 per new vehicle in the long term, depending on the
vehicle size. In comparison, new vehicle prices today can range up to
$250,000 for larger heavy-duty vehicles. The cost of reducing the
sulfur content of diesel fuel would result in an estimated increase of
approximately four cents per gallon.

DATES: Comments: We must receive your comments by August 14, 2000.
Hearings: We will hold public hearings on June 19, 20, 22, 27, and
29, 2000. See ADDRESSES below for the locations of the hearings.

ADDRESSES: Comments: You may send written comments in paper form and/or
by e-mail. We must receive them by the date indicated under ``DATES''
above. Send paper copies of written comments (in duplicate if possible)
to the contact person listed below. Send e-mail comments to
diesel@epa.gov.
EPA's Air Docket makes materials related to this rulemaking
available for review in Docket No. A-99-06 located at U.S.
Environmental Protection Agency (EPA), Air Docket (6102), Room M-1500,
401 M Street, SW, Washington, DC 20460 (on the ground floor in
Waterside Mall) from 8 a.m. to 5:30 p.m., Monday through Friday, except
on government holidays. You can reach the Air Docket by telephone at
(202) 260-7548 and by facsimile at (202) 260-4400. We may charge a
reasonable fee for copying docket materials, as provided in 40 CFR part
2.
Hearings: We will hold five public hearings at the following
locations:

June 19, 2000, Crowne Plaza Hotel, 1605 Broadway, New York, NY,
10019
June 20, 2000, Rosemont Convention Center, 5555 N. River Rd.,
Rosemont, IL 60018
June 22, 2000, Renaissance Atlanta Hotel, 590 W. Peachtree St, NW,
Atlanta, GA, 30308
June 27, 2000, Hyatt Regency, 711 S. Hope Street, Los Angeles, CA,
90017
June 29, 2000, Doubletree Hotel, 3203 Quebec St., Denver, CO, 80207

We request that parties who want to testify at a hearing notify the
contact person listed below ten days before the date of the hearing.
Please see section X, ``Public Participation'' below for more
information on the comment procedure and public hearings.

FOR FURTHER INFORMATION CONTACT: Margaret Borushko, U.S. EPA, National
Vehicle and Fuel Emissions Laboratory, 2000 Traverwood, Ann Arbor MI
48105; Telephone (734) 214-4334, FAX (734) 214-4816, E-mail
borushko.margaret@epa.gov.

SUPPLEMENTARY INFORMATION:
Regulated Entities
This proposed action would affect you if you produce or import new

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heavy-duty engines which are intended for use in highway vehicles such
as trucks and buses or heavy-duty highway vehicles, or convert heavy-
duty vehicles or heavy-duty engines used in highway vehicles to use
alternative fuels. It would also affect you if you produce, distribute,
or sell highway diesel fuel.
The table below gives some examples of entities that may have to
follow the proposed regulations. But because these are only examples,
you should carefully examine the proposed and existing regulations in
40 CFR parts 69, 80, and 86. If you have questions, call the person
listed in the FOR FURTHER INFORMATION CONTACT section above.

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Examples of potentially regulated
Category NAICS Codes ^a SIC Codes ^b entities
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Industry................................... 336112 3711 Engine and truck manufacturers.
336120
Industry................................... 811112 7533 Commercial importers of vehicles
and vehicle components.
811198 7549
Industry................................... 324110 2911 Petroleum refiners.
Industry................................... 422710 5171 Diesel fuel marketers and
distributors.
422720 5172
Industry................................... 484220 4212 Diesel fuel carriers.
484230 4213
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^a North American Industry Classification System (NAICS).
^b Standard Industrial Classification (SIC) system code.

Access to Rulemaking Documents Through the Internet
Today's proposal is available electronically on the day of
publication from the Environmental Protection Agency Internet Web site
listed below. Electronic copies of the preamble, regulatory language,
Draft Regulatory Impact Analysis, and other documents associated with
today's proposal are available from the EPA Office of Transportation
and Air Quality (formerly the Office of Mobile Sources) Web site listed
below shortly after the rule is signed by the Administrator. This
service is free of charge, except any cost that you incur for
connecting to the Internet.
Environmental Protection Agency Web Site:

http://www.epa.gov/fedrgstr/

(Either select a desired date or use the Search feature.)

Office of Transportation and Air Quality (OTAQ) Web Site:

http://www.epa.gov/otaq/

(Look in ``What's New'' or under the ``Heavy Trucks/Busses'' topic.)

Please note that due to differences between the software used to
develop the document and the software into which document may be
downloaded, changes in format, page length, etc. may occur.

Table of Contents

I. A Brief Overview
A. What Is Being Proposed?
1. Heavy-Duty Emission Standards
2. Fuel Quality Standards
B. Why Is EPA Making This Proposal?
1. Heavy-Duty Vehicles Contribute to Serious Air Pollution
Problems
2. Technology-Based Solutions
3. Basis for Action Under the Clean Air Act
C. Putting This Proposal In Perspective
1. Diesel Popularity
2. Past Progress and New Developments
3. Tier 2 Emissions Standards
4. Mobile Source Air Toxics Rulemaking
5. Nonroad Engine Standards and Fuel
6. Actions in California
7. Retrofit Programs
8. Actions in Other Countries
II. The Air Quality Need and Projected Benefits
A. Overview
B. Public Health and Welfare Concerns
1. Ozone and Its Precursors
a. Health and Welfare Effects From Short-Term Exposures to Ozone
b. Current and Future Nonattainment Status With the 1-Hour Ozone
NAAQS
i. Ozone Predictions Made in the Tier 2 Rulemaking and Other
Information on Ozone Attainment Prospects
ii. Areas At Risk of Exceeding the 1-Hour Ozone Standard
iii. Conclusion
c. Public Health and Welfare Concerns from Prolonged and
Repeated Exposures to Ozone
2. Particulate Matter
a. Health and Welfare Effects
i. Particulate Matter Generally
ii. Special Considerations for Diesel PM
b. Potential Cancer Effects of Diesel Exhaust
c. Noncancer Effects of Diesel Exhaust
d. Attainment and Maintenance of the PM10 NAAQS
i. Current PM10 Nonattainment
ii. Risk of Future Exceedances of the PM10 Standard
e. Public Health and Welfare Concerns from Exposure to Fine PM
f. Visibility and Regional Haze Effects of Ambient PM
g. Other Welfare Effects Associated with PM
h. Conclusions Regarding PM
3. Other Criteria Pollutants
4. Other Air Toxics
a. Benzene
b. 1,3-Butadiene
c. Formaldehyde
d. Acetaldehyde
e. Acrolein
f. Dioxins
5. Other Environmental Effects
a. Acid Deposition
b. Eutrophication and Nitrification
c. POM Deposition
C. Contribution From Heavy-Duty Vehicles
1. NO_X Emissions
2. PM Emissions
3. Environmental Justice
D. Anticipated Emissions Benefits
1. NO_X Reductions
2. PM Reductions
3. NMHC Reductions
4. Additional Emissions Benefits
a. CO Reductions
b. SO_X Reductions
c. Air Toxics Reductions
E. Clean Heavy-Duty Vehicles and Low-Sulfur Diesel Fuel Are
Critically Important for Improving Human Health and Welfare
III. Heavy-Duty Engine and Vehicle Standards
A. Why Are We Setting New Heavy-Duty Standards?
B. Technology Opportunity for Heavy-Duty Vehicles and Engines
C. What Engine and Vehicle Standards Are We Proposing?
1. Heavy-Duty Engine Standards
a. Federal Test Procedure
b. Not-to-Exceed and Supplemental Steady-State Test
c. Crankcase Emissions Control
2. Heavy-Duty Vehicle Standards
a. Federal Test Procedure
b. Supplemental Federal Test Procedure
3. Heavy-Duty Evaporative Emission Standards
D. Standards Implementation Issues
1. Alternative Approach To Phase-In
2. Implementation Schedule for Gasoline Engine and Vehicle
Standards
E. Feasibility of the Proposed New Standards
1. Feasibility of Stringent Standards for Heavy-Duty Diesel
a. Meeting the Proposed PM Standard
b. Meeting the Proposed NO_X Standard
c. Meeting the Proposed NMHC Standard

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d. Meeting the Crankcase Emissions Requirements
e. The Complete System
2. Feasibility of Stringent Standards for Heavy-Duty Gasoline
3. Feasibility of the Proposed Evaporative Emission Standards
F. Need for Low-Sulfur Diesel Fuel
1. Diesel Particulate Filters and the Need for Low-Sulfur Fuel
a. Inhibition of Trap Regeneration Due to Sulfur
b. Loss of PM Control Effectiveness
c. Increased Maintenance Cost for Diesel Particulate Filters Due
to Sulfur
2. Diesel NO_X Catalysts and the Need for Low-Sulfur
Fuel
a. Sulfate Particulate Production for NO_X Control
Technologies
b. Sulfur Poisoning (Sulfate Storage) on NO_X
Adsorbers
c. Sulfur Impacts on Catalytic Efficiency
3. What About Sulfur in Engine Lubricating Oils?
G. Fuel Economy Impact of Advanced Emission Control Technologies
1. Diesel Particulate Filters and Fuel Economy
2. NO_X Control Technologies and Fuel Economy
3. Emission Control Systems for 2007 and Net Fuel Economy
Impacts
H. Future Reassessment of Diesel NO_X Control
Technology
I. Encouraging Innovative Technologies
IV. Diesel Fuel Requirements
A. Why Do We Believe New Diesel Fuel Sulfur Controls Are
Necessary?
B. What New Sulfur Standard Are We Proposing for Diesel Fuel?
1. Why Is EPA Proposing a 15 ppm Cap and Not a Higher or Lower
Level?
2. Why Propose a Cap and Not an Average?
3. Should the Proposed 15 ppm Cap Standard Also Have an Average
Standard?
4. Why We Believe Our Diesel Fuel Sulfur Program Should Be Year-
round and Nationwide
C. When Would the New Diesel Sulfur Standard Go Into Effect?
D. Why We Believe the Proposed Diesel Sulfur Standard is
Technologically Feasible
1. What Technology Would Refiners Use?
2. Are These Technologies Commercially Demonstrated?
3. Are There Unique Concerns for Small Refiners?
4. Can Refiners Comply with an April 1, 2006 Start Date?
5. Can a 15 ppm Cap on Sulfur be Maintained by the Distribution
System?
6. What are the Potential Impacts of the Proposed Sulfur Change
on Lubricity, Other Fuel Properties, and Specialty Fuels?
a. What Is Lubricity and Why Might It be a Concern?
b. Voluntary Approach for the Maintenance of Fuel Lubricity
c. What Are the Possible Impacts of Potential Changes in Fuel
Properties Other Than Sulfur on the Materials Used in Engines and
Fuel Supply Systems?
d. What Impact Would the 15 ppm Cap Have on Diesel Performance
Additives?
e. What Are the Concerns Regarding the Potential Impact on the
Availability and Quality of Specialty Fuels?
E. Who Would Be Required to Meet This Proposed New Diesel Sulfur
Standard?
F. What Might Be Done To Encourage the Early Introduction of
Low-Sulfur Diesel Fuel?
V. Economic Impact
A. Cost for Diesel Vehicles to Meet Proposed Emissions Standards
1. Summary of New System and Operating Costs
2. New System Costs for NO_X and PM Emission Control
3. Operating Costs Associated With NO_X and PM Control
B. Cost for Gasoline Vehicles to Meet Proposed Emissions
Standards
1. Summary of New System Costs
2. Operating Costs Associated with Meeting the Heavy-Duty
Gasoline Standard
C. Benefits of Low-Sulfur Diesel Fuel for the Existing Diesel
Fleet
D. Cost of Proposed Fuel Change
1. Refinery Costs
2. Cost of Possibly Needed Lubricity Additives
3. Distribution Costs
E. Aggregate Costs
F. Cost Effectiveness
1. What Is the Cost Effectiveness of This Proposed Program?
2. Comparison With Other Means of Reducing Emissions
G. Does the Value of the Benefits Outweigh the Cost of the
Proposed Standards?
1. What Is the Purpose of This Benefit-Cost Comparison?
2. What Is Our Overall Approach to the Benefit-Cost Analysis?
3. What Are the Significant Limitations of the Benefit-Cost
Analysis?
4. How Will the Benefit-Cost Analysis Change From the Tier 2
Benefit-Cost Analysis?
5. How Will We Perform the Benefit-Cost Analysis?
6. What Types of Results Will Be Presented in the Benefit-Cost
Analysis?
VI. Alternative Program Options
A. What Other Fuel Implementation Options Have We Considered?
1. What Are the Advantages and Disadvantages of a Phase-in
Approach to Implementing the Low Sulfur Fuel Program?
a. Availability of Low Sulfur Diesel Fuel
b. Misfueling
c. Distribution System Impacts
d. Uncertainty in the Transition to Low Sulfur
e. Cost Considerations Under a Phase-in Approach
2. What Phase-in Options Is EPA Seeking Comment on in Today's
Proposal?
a. Refiner Compliance Flexibility
i. Overview of Compliance Flexibility
ii. What Are the Key Considerations in Designing the Compliance
Flexibility?
iii. How Does This Compliance Flexibility Relate to the Options
for Small Refiner Flexibility?
iv. How Would the Averaging, Banking and Trading Program Work?
v. Compliance, Recordkeeping, and Reporting Requirements
b. Refiner-Ensured Availability
c. Retailer Availability Requirement
2. Why Is a Regulation Necessary to Implement the Fuel Program?
3. Why Not Just Require Low-Sulfur Diesel Fuel for Light-Duty
Vehicles and Light-Duty Trucks?
4. Why Not Phase-Down the Concentration of Sulfur in Diesel Fuel
Over Time as Was Done With Gasoline in the Tier 2 Program?
B. What Other Fuel Standards Have We Considered In Developing
This Proposal?
1. What About Setting the 15 ppm Sulfur Level as an Average?
a. Emission Control Technology Enablement Under a 15 ppm Average
Standard
b. Vehicle and Operating Costs for Diesel Vehicles to Meet the
Proposed Emissions Standards with a 15 ppm Average Standard
c. Diesel Fuel Costs Under a 15 ppm Average Standard
d. Emission Reductions Under a 15 ppm Average Standard
e. Cost Effectiveness of a 15 ppm Average Standard
2. What About a 5 ppm Sulfur Level?
3. What About a 50 ppm Sulfur Level?
4. What Other Fuel Properties Were Considered for Highway Diesel
Fuel?
C. Should Any States or Territories Be Excluded from this Rule?
1. What Are the Anticipated Impacts of Using High-Sulfur Fuel in
New and Emerging Diesel Engine Technologies if Areas Are Excluded
From This Rule?
2. Alaska
a. Why is Alaska Unique?
b. What Flexibilities Are We Proposing for Alaska?
c. How Do We Propose to Address Alaska's Petition Regarding the
500 ppm Standard?
3. American Samoa, Guam, and the Commonwealth of Northern
Mariana Islands
a. Why are We Considering Excluding American Samoa, Guam, and
the Commonwealth of Northern Mariana Islands?
b. What Are the Relevant Factors?
c. What Are the Options and Proposed Provisions for the
Territories?
D. What About the Use of JP-8 Fuel in Diesel Equipped Military
Vehicles?
VII. Requirements for Engine and Vehicle Manufacturers
A. Compliance With Standards and Enforcement
B. Certification Fuel
C. Averaging, Banking, and Trading
D. Chassis Certification
E. FTP Changes to Accommodate Regeneration of Aftertreatment
Devices
F. On-Board Diagnostics
G. Supplemental Test Procedures
H. Misfueling Concerns
I. Light-Duty Provisions
J. Correction of NO_X Emissions for Humidity Effects
VIII. Requirements For Refiners, Importers, and Fuel Distributors

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A. Compliance and Enforcement
1. Overview
2. What Are the Requirements for Refiners and Importers?
a. General Requirements
b. Dyes and Markers
3. What Requirements Apply Downstream?
a. General Requirements
b. Use of Used Motor Oil in Diesel-Fueled New Technology
Vehicles
c. Use of Kerosene and Other Additives in Diesel Fuel
4. What Are the Proposed Testing and Sampling Methods and
Requirements?
a. Testing Requirements and Test Methods
b. Sampling Methods
5. What Are the Proposed Recordkeeping Requirements?
6. Are There Any Proposed Exemptions Under This Subpart?
7. Would California Be Exempt From the Rule?
8. What Are the Proposed Liability and Penalty Provisions for
Noncompliance?
a. Presumptive Liability Scheme of Current EPA Fuels Programs
b. Affirmative Defenses for Liable Parties
c. Penalties for Violations
9. How Would Compliance With the Diesel Sulfur Standards Be
Determined?
B. Lubricity
C. Would States Be Preempted From Adopting Their Own Sulfur
Control Programs for Highway Diesel Fuel?
D. Refinery Air Permitting
E. Provisions for Qualifying Refiners
1. Allow Small Refiners to Continue Selling 500 ppm Highway
Diesel
2. Temporary Waivers Based on Extreme Hardship Circumstances
3. 50 ppm Sulfur Cap for Small Refiners
IX. Standards and Fuel for Nonroad Diesel Engines
X. Public Participation
A. Submitting Written and E-mail Comments
B. Public Hearings
XI. Administrative Requirements
A. Administrative Designation and Regulatory Analysis
B. Regulatory Flexibility Act
1. Potentially Affected Small Businesses
2. Small Business Advocacy Review Panel and the Evaluation of
Regulatory Alternatives
C. Paperwork Reduction Act
D. Intergovernmental Relations
1. Unfunded Mandates Reform Act
2. Executive Order 13084: Consultation and Coordination With
Indian Tribal Governments
E. National Technology Transfer and Advancement Act
F. Executive Order 13045: Children's Health Protection
G. Executive 13132: Federalism
XII. Statutory Provisions and Legal Authority

I. A Brief Overview

This proposal covers the second of two phases in a comprehensive
nationwide program for controlling emissions from heavy-duty engines
(HDEs) and vehicles. It builds upon the phase 1 program we proposed
last October (64 FR 58472, October 29, 1999). That action reviewed and
proposed to confirm the 2004 model year emission standards set in 1997
(62 FR 54693, October 21, 1997), proposed stringent new emission
standards for gasoline-fueled heavy-duty vehicles (HDVs), and proposed
other changes to the heavy-duty program, including provisions to ensure
in-use emissions control. Today's proposal takes the provisions of the
October 1999 proposal as a point of departure.
This second phase of the program looks beyond 2004, based on the
use of high-efficiency exhaust emission control devices and the
consideration of the vehicle and its fuel as a single system. In
developing this proposal, we took into consideration comments received
in response to an advance notice of proposed rulemaking (ANPRM)
published in May of last year (64 FR 26142, May 13, 1999), and comments
we received in response to our discussion of future standards in the
heavy-duty 2004 standards proposal last October. We welcome comment on
all facets of this proposal and its supporting analyses, including the
levels and timing of the proposed emissions standards and diesel fuel
quality requirements. We ask that commenters provide any technical
information that supports the points made in their comments.
This proposed program would result in particulate matter (PM) and
oxides of nitrogen (NO_X) emission levels that are 90% and
95% below current standards levels, respectively. In order to meet
these more stringent standards for diesel engines, the proposal calls
for a 97% reduction in the sulfur content of diesel fuel. This proposal
would make clean diesel fuel available in time for implementation of
the light-duty Tier 2 standards. The heavy-duty engine standards would
be effective starting in the 2007 model year and the low sulfur diesel
fuel needed to facilitate the standards would be widely available by
the middle of 2006. As a result, diesel vehicles would achieve
gasoline-like exhaust emission levels, in addition to their inherent
advantages over gasoline vehicles with respect to fuel economy, lower
greenhouse gas emissions, and lower evaporative hydrocarbon emissions.
We are also proposing more stringent standards for heavy-duty gasoline
vehicles.
The standards proposed would result in substantial benefits to
public health and welfare and the environment through significant
reductions in emissions of NO_X, PM, nonmethane hydrocarbons
(NMHC), carbon monoxide (CO), sulfur oxides (SO_X), and air
toxics. We project that by 2030, this proposed phase 2 program would
reduce annual emissions of NO_X, NMHC, and PM by 2.8 million,
305,000 and 110,000 tons, respectively. Especially in the early years
of this program, large reductions in the amount of direct and secondary
PM caused by the existing fleet of heavy-duty vehicles would occur
because of the improvement in diesel fuel quality.

A. What Is Being Proposed?

There are two basic parts to this proposal: (1) New exhaust
emission standards for heavy-duty highway engines and vehicles, and (2)
new quality standards for highway diesel fuel. The systems approach of
combining the engine and fuel standards into a single program is
critical to the success of our overall efforts to reduce emissions,
because the emission standards would not be feasible without the fuel
change. This is because the emission standards, if promulgated, are
expected to result in the use of high-efficiency exhaust emission
control devices that would be damaged by sulfur in the fuel. This
proposal, by providing extremely low sulfur diesel fuel, would also
enable cleaner diesel passenger vehicles and light-duty trucks. This is
because the same pool of highway diesel fuel also services these light-
duty diesel vehicles, and these vehicles can employ technologies
similar to the high-efficiency heavy-duty exhaust emission control
technologies that would be enabled by the fuel change. We believe these
technologies are needed for diesel vehicles to comply with our recently
adopted Tier 2 emissions standards for light-duty highway vehicles (65
FR 6698, February 10, 2000).
We believe that this systems approach is a comprehensive way to
enable promising new technologies for clean diesel affecting all sizes
of highway diesel engines and, eventually, diesel engines used in
nonroad applications too. The fuel change, in addition to enabling new
technologies, would also produce emissions and maintenance benefits in
the existing fleet of highway diesel vehicles. These benefits would
include reduced sulfate and sulfur oxides emissions, reduced engine
wear and less frequent oil changes, and longer-lasting exhaust gas
recirculation (EGR) components on engines equipped with EGR. Heavy-duty
gasoline vehicles would also be expected to reach cleaner levels due to
the transfer of recent technology developments for light-duty
applications, and the recent action taken to reduce sulfur in gasoline
as part of the Tier 2 rule.

[[Page 35434]]

The basic elements of the proposal are outlined below. Detailed
provisions and justifications for our proposal are discussed in
subsequent sections.
1. Heavy-Duty Emission Standards
We are proposing a PM emissions standard for new heavy-duty engines
of 0.01 grams per brake-horsepower-hour (g/bhp-hr), to take full effect
in the 2007 HDE model year. We are also proposing standards for
NO_X and NMHC of 0.20 g/bhp-hr and 0.14 g/bhp-hr,
respectively. These NO_X and NMHC standards would be phased
in together between 2007 and 2010, for diesel engines. The phase-in
would be on a percent-of-sales basis: 25 percent in 2007, 50 percent in
2008, 75 percent in 2009, and 100 percent in 2010. Because of the more
advanced state of gasoline engine emissions control technology,
gasoline engines would be fully subject to these standards in the 2007
model year, although we request comment on phasing these standards in
as well. A potential delay in the implementation date of the gasoline
engine and vehicle standards to the 2008 model year arising from issues
connected with the 2004 model year standards is discussed in section
III.D.2. In addition, we are proposing a formaldehyde (HCHO) emissions
standard of 0.016 g/bhp-hr for all heavy-duty engines, to be phased in
with the NO_X and NMHC standards, and the inclusion of
turbocharged diesels in the existing crankcase emissions prohibition,
effective in 2007.
Proposed standards for complete HDVs would be implemented on the
same schedule as for engine standards. For certification of complete
vehicles between 8500 and 10,000 pounds gross vehicle weight rating
(GVWR), the proposed standards are 0.2 grams per mile (g/mi) for
NO_X, 0.02 g/mi for PM, 0.195 g/mi for NMHC, and 0.016 g/mi
for formaldehyde.\1\ For vehicles between 10,000 and 14,000 pounds, the
proposed standards are 0.4 g/mi for NO_X, 0.02 g/mi for
PM, 0.230 g/mi for NMHC, and 0.021 g/mi for formaldehyde. These
standards levels are roughly comparable to the proposed engine-based
standards in these size ranges. Note that these standards would not
apply to vehicles above 8500 pounds that we classify as medium-duty
passenger vehicles as part of our Tier 2 program.
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\1\ Vehicle weight ratings in this proposal refer to GVWR (the
curb weight of the vehicle plus its maximum recommended load of
passengers and cargo) unless noted otherwise.
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Finally, we are proposing to revise the evaporative emissions
standards for heavy-duty engines and vehicles, effective on the same
schedule as the gasoline engine and vehicle exhaust emission standards.
The proposed standards for 8500 to 14,000 pound vehicles are 1.4 and
1.75 grams per test for the 3-day diurnal and supplemental 2-day
diurnal tests, respectively. Slightly higher standards levels of 1.9
and 2.3 grams per test would apply for vehicles over 14,000 pounds.
These proposed standards represent more than a 50 percent reduction in
the numerical standards as they exist today.
2. Fuel Quality Standards
We are proposing that diesel fuel sold to consumers for use in
highway vehicles be limited in sulfur content to a level of 15 parts
per million (ppm), beginning June 1, 2006. This proposed sulfur
standard is based on our assessment of how sulfur-intolerant advanced
exhaust emission control technologies will be, and a corresponding
assessment of the feasibility of low-sulfur fuel production and
distribution. We are seeking comment on voluntary options for providing
refiners with flexibility in complying with the low sulfur highway
diesel fuel program. In addition, we request comment on some potential
flexibility provisions to assist small refiners in complying with the
program.
With minor exceptions, existing compliance provisions for ensuring
diesel fuel quality that have been in effect since 1993 would remain
unchanged (55 FR 34120, August 21, 1990).

B. Why Is EPA Making This Proposal?

1. Heavy-Duty Vehicles Contribute to Serious Air Pollution Problems
As will be discussed in detail in section II, emissions from heavy-
duty vehicles contribute greatly to a number of serious air pollution
problems, and will continue to do so into the future absent further
controls to reduce these emissions. First, heavy-duty vehicles
contribute to the health and welfare effects of ozone, PM,
NO_X, SO_X, and volatile organic compounds (VOCs),
including toxic compounds such as formaldehyde. These adverse effects
include premature mortality, aggravation of respiratory and
cardiovascular disease (as indicated by increased hospital admissions
and emergency room visits, school absences, work loss days, and
restricted activity days), changes in lung function and increased
respiratory symptoms, changes to lung tissues and structures, altered
respiratory defense mechanisms, chronic bronchitis, and decreased lung
function. Ozone also causes crop and forestry losses, while PM also
causes damage to materials, and soiling. Second, both NO_X
and PM contribute to substantial visibility impairment in many parts of
the U.S. Third, NO_X emissions from heavy-duty trucks
contribute to the acidification, nitrification and eutrophication of
water bodies.
Millions of Americans live in areas with unhealthful air quality
that currently endangers public health and welfare. Without emission
reductions from the proposed standards for heavy-duty vehicles, there
is a significant risk that an appreciable number of areas across the
country will violate the 1-hour ozone national ambient air quality
standard (NAAQS) during the period when these standards will take
effect. Furthermore, our analysis shows that PM10
concentrations in 10 areas with a combined population of 27 million
people face a significant risk of exceeding the PM10 NAAQS
without significant additional controls in 2007 or thereafter. Under
the mandates and authorities in the Clean Air Act, federal, State, and
local governments are working to bring ozone and particulate levels
into compliance with the 1-hour ozone and PM10 NAAQS through
State Implementation Plan (SIP) attainment and maintenance plans, and
to ensure that future air quality reaches and continues to achieve
these health-based standards. The reductions proposed in this
rulemaking would play a critical part in these important efforts.
Emissions from heavy-duty vehicles account for substantial portions
of the country's ambient PM and NO_X levels. (NO_X
is a key precursor to ozone formation). By 2007, we estimate that
heavy-duty vehicles will account for 29 percent of mobile source
NO_X emissions and 14 percent of mobile source PM emissions.
These proportions are even higher in some urban areas, such as in
Albuquerque, where HDVs contribute 37 percent of the mobile source
NO_X emissions and 20 percent of the mobile source PM
emissions. The PM and NO_X standards for heavy-duty vehicles
proposed in this rule would have a substantial impact on these
emissions. By 2030, NO_X emissions from heavy-duty vehicles
under today's proposed standards would be reduced by 2.8 million tons,
and PM emissions would decline by about 110,000 tons, dramatically
reducing this source of NO_X and PM emissions. Urban areas,
which include many poorer neighborhoods, can be disproportionately
impacted by HDV emissions, and these neighborhoods would thus receive a
relatively larger portion of the benefits expected from new HDV
emissions controls. Over time,

[[Page 35435]]

the relative contribution of diesel engines to air quality problems
will go even higher if diesel-equipped light-duty vehicles become more
popular, as is expected by some automobile manufacturers.
In addition to its contribution to PM inventories, diesel exhaust
PM is of special concern because it has been implicated in an increased
risk of lung cancer and respiratory disease in human studies. The EPA
draft Health Assessment Document for Diesel Emissions is currently
being revised based on comments received from the Clean Air Scientific
Advisory Committee (CASAC) of EPA's Science Advisory Board. The current
EPA position is that diesel exhaust is a likely human carcinogen and
that this cancer hazard applies to environmental levels of exposure.\2\
In the draft Health Assessment Document for Diesel Emissions, EPA
provided a qualitative perspective that the upper bounds on
environmental cancer risks may exceed 10^-6 and could be as
high as 10^-3. Several other agencies and governing bodies
have designated diesel exhaust or diesel PM as a ``potential'' or
``probable'' human carcinogen. In addition, diesel PM poses
nonmalignant respiratory hazards to humans, not unlike, in some
respects, hazards from exposure to ambient PM2.5, to which
diesel PM contributes. State and local governments, in their efforts to
protect the health of their citizens and comply with requirements of
the Clean Air Act (CAA or ``the Act''), have recognized the need to
achieve major reductions in diesel PM emissions, and have been seeking
Agency action in setting stringent new standards to bring this
about.\3\
---------------------------------------------------------------------------

\2\ Environmental Protection Agency (1999) Health Assessment
Document for Diesel Emissions: SAB Review Draft. EPA/600/8-90/057D
Office of Research and Development, Washington, D.C. The document is
available electronically at www.epa.gov/ncea/diesel.htm
\3\ For example, see letter dated July 13, 1999 from John Elston
and Richard Baldwin on behalf of the State and Territorial Air
Pollution Program Administrators and the Association of Local Air
Pollution Control Officials (docket A-99-06, item II-D-78).
---------------------------------------------------------------------------

2. Technology-Based Solutions
Although the air quality problems caused by diesel exhaust are
formidable, we believe they can be resolved through the application of
high-efficiency emissions control technologies. As discussed in detail
in section III, the development of diesel emissions control technology
has advanced in recent years so that very large emission reductions (in
excess of 90 percent) are possible, especially through the use of
catalytic emission control devices installed in the vehicle's exhaust
system (and integrated with the engine controls). These devices are
often referred to as ``exhaust emission control'' or ``aftertreatment''
devices. Exhaust emission control devices, in the form of the well-
known catalytic converter, have been used in gasoline-fueled
automobiles for 25 years, but have had only limited application in
diesel vehicles.
Because the Clean Air Act requires us to set heavy-duty engine
standards that reflect the greatest degree of emission reduction
achievable through the application of available technology (subject to
a number of criteria as discussed in section I.B.3), this notice
proposes these standards, and proposes a justification for their
adoption based on the air quality need, their technological
feasibility, costs, and other criteria listed in the Act (see section
III of this document). As part of this proposal, we are also proposing
changes to diesel fuel quality in order to enable these advanced
technologies (section IV). Heavy-duty gasoline engines would also be
able to reach the significantly cleaner levels envisioned in this
proposal by relying on the transfer of recent technology developments
for light-duty applications, given the recent action taken to reduce
sulfur in gasoline (65 FR 6698, February 10, 2000).
We believe the proposed standards would require the application of
high-efficiency PM and NO_X exhaust emission controls to
heavy-duty diesel vehicles. High-efficiency PM exhaust emission control
technology has been available for several years, although engine
manufacturers have generally not needed this technology in order to
meet our PM emission standards. This technology has continued to
improve over the years, especially with respect to durability and
robust operation in use. It has also proven extremely effective in
reducing exhaust hydrocarbon emissions. Thousands of such advanced-
technology systems are now in use in fleet programs, especially in
Europe. However, as discussed in detail in section III, these advanced-
technology systems are very sensitive to sulfur in the fuel. For the
technology to be viable and capable of meeting the proposed standards,
we believe, based on information currently available, that it will
require diesel fuel with sulfur content at the 15 ppm level.
Similarly, high-efficiency NO_X exhaust emission control
technology will be needed if heavy-duty vehicles are to attain the
proposed standards. We believe this technology, like the PM technology,
is dependent on 15 ppm diesel fuel sulfur levels to be feasible,
marketable, and capable of achieving the proposed standards. High-
efficiency NO_X exhaust emission control technology has been
quite successful in gasoline direct injection engines that operate with
an exhaust composition fairly similar to diesel exhaust. However, as
discussed in section III, application of this technology to diesels has
some additional challenges and so has not yet gotten to the field trial
stage. We are confident that the certainty of low-sulfur diesel fuel
that would be provided by promulgation of the proposed fuel standard
would allow the application of this technology to diesels to progress
rapidly, and would result in systems capable of achieving the proposed
standards. However, we acknowledge that our proposed NO_X
standard represents an ambitious target for this technology, and so we
are asking for comment on the appropriateness of a technology review of
diesel NO_X exhaust emission controls.
The need to reduce the sulfur in diesel fuel is driven by the
requirements of the exhaust emission control technology that we project
would be needed to meet the proposed standards. The challenge in
accomplishing the sulfur reduction is driven by the feasibility of
needed refinery modifications, and by the costs of making the
modifications and running the equipment. In consideration of the
impacts that sulfur has on the efficiency, reliability, and fuel
economy impact of diesel engine exhaust emission control devices, we
believe that controlling the sulfur content of highway diesel fuel to
the 15 ppm level will be necessary. Furthermore, although the refinery
modifications and process changes needed to meet a 15 ppm restriction
are expected to be substantial, we propose that this level is both
feasible and cost effective. However, we are asking for comment on
various concepts to provide implementation flexibility for refiners.
3. Basis for Action Under the Clean Air Act
Section 202(a)(1) of the Act directs us to establish standards
regulating the emission of any air pollutant from any class or classes
of new motor vehicles or engines that, in the Administrator's judgment,
cause or contribute to air pollution which may reasonably be
anticipated to endanger public health or welfare. Section 202(a)(3)
requires that EPA set standards for heavy-duty trucks that reflect the
greatest degree of emission reduction achievable through the
application of technology which we determine will be available for the

[[Page 35436]]

model year to which the standards apply. We are to give appropriate
consideration to cost, energy, and safety factors associated with the
application of such technology. We may revise such technology-based
standards, taking costs into account, on the basis of information
concerning the effects of air pollution from heavy-duty vehicles or
engines and other sources of mobile source related pollutants on the
public health and welfare. Section 202(a)(3)(C) requires that
promulgated standards apply for no less than three years and go into
effect no less than 4 years after promulgation. This proposal has been
developed in conformance with these statutory requirements.
We believe the evidence provided in section III and the draft
Regulatory Impact Analysis (RIA) indicates that the stringent
technology-forcing standards proposed today are feasible and reflect
the greatest degree of emission reduction achievable in the model years
to which they apply. We have given appropriate consideration to costs
in choosing these standards. Our review of the costs and cost-
effectiveness of these proposed standards indicate that they would be
reasonable and comparable to the cost-effectiveness of other emission
reduction strategies that have been required or could be required in
the future. We have also reviewed and given appropriate consideration
to the energy factors of this rule in terms of fuel efficiency and
effects on diesel production and distribution, as discussed below, as
well as any safety factors associated with these proposed standards.
The information regarding air quality and the contribution of
heavy-duty engines to air pollution in section II and the Draft RIA
provides strong evidence that emissions from such engines significantly
and adversely impact public health or welfare. First, there is a
significant risk that several areas will fail to attain or maintain
compliance with the NAAQS for 1-hour ozone concentrations or
PM10 concentrations during the period that these proposed
new vehicle and engine standards would be phased into the vehicle
population, and that heavy-duty engines contribute to such
concentrations, as well as to concentrations of other NAAQS-related
pollutants. Second, EPA currently believes that diesel exhaust is a
likely human carcinogen. The risk associated with exposure to diesel
exhaust includes the particulate and gaseous components. Some of the
toxic air pollutants associated with emissions from heavy-duty vehicles
and engines include benzene, formaldehyde, acetaldehyde, dioxin,
acrolein, and 1,3-butadiene. Third, emissions from heavy-duty engines
contribute to regional haze and impaired visibility across the nation,
as well as acid deposition, POM deposition, eutrophication and
nitrification, all of which are serious environmental welfare problems.
Based on this evidence, EPA believes that, for purposes of section
202(a)(1), emissions of NO_X, VOCs, SO_X and PM
from heavy-duty trucks can reasonably be anticipated to endanger the
public health or welfare. In addition, this evidence indicates that it
would not be appropriate to modify the technology based standards
pursuant to section 202(a)(3)(B). EPA believes that it is required
under section 202(a)(3)(A) to set technology based standards that meet
the criteria of that provision, and is not required to make an
affirmative determination under section 202(a)(1). Instead EPA is
authorized to take air quality into consideration under section
202(a)(3)(B) in deciding whether to modify or not set standard under
section 202(a)(3)(A). In this case, however, EPA believes the evidence
would fully support a determination under section 202(a)(1) to set
standards, and a determination not to modify such standards under
section 202(a)(3)(B).
In addition, there is significant evidence that emissions from
heavy-duty trucks contribute to levels of ozone such that large
segments of the national population are expected to experience
prolonged exposure over several hours at levels that present serious
concern for the public health and welfare. The same is true for
exposure to fine PM. These public health and welfare problems are
expected to occur in many parts of the country, including areas that
are in compliance with the 1-hour ozone and PM10 NAAQS
(PM10 is particulate matter that is 10 microns or smaller).
This evidence is an additional reason why the controls proposed today
are justified and appropriate under the Act. While EPA sees this as
additional support for this action, EPA also believes that the evidence
of air pollution problems summarized above and described in greater
detail elsewhere is an adequate justification for this rule independent
of concern over prolonged exposure to ozone levels.
Section 211(c) of the CAA allows us to regulate fuels where
emission products of the fuel either: (1) Cause or contribute to air
pollution that reasonably may be anticipated to endanger public health
or welfare, or (2) will impair to a significant degree the performance
of any emission control device or system which is in general use, or
which the Administrator finds has been developed to a point where in a
reasonable time it would be in general use were such a regulation to be
promulgated. This proposal meets each of these criteria. The discussion
of the first test is substantially the same as the above discussion for
the heavy-duty engine standards, because SOx emissions from heavy-duty
diesel vehicles are due to sulfur in diesel fuel. The substantial
adverse effect of high diesel sulfur levels on diesel control devices
or systems expected to be used to meet the heavy-duty standards is
discussed in depth in section III.F and in the Draft RIA. In addition,
our authority under section 211(c) is discussed in more detail in
appendix A to the draft RIA.

C. Putting This Proposal in Perspective

There are several helpful perspectives to establish in
understanding the context for this proposal: the growing popularity of
diesel engines, past progress and new developments in diesel emissions
control, Tier 2 light-duty emission standards and other related EPA
initiatives (besides the above-discussed rulemaking for highway heavy-
duty engine emission standards in 2004), and recent actions and plans
to control diesel emissions by the States and in other countries.
1. Diesel Popularity
The diesel engine is increasingly becoming a vital workhorse in the
United States, moving much of the nation's freight, and carrying out
much of its farm, construction, and other labor. Diesel engine sales
have grown impressively over the last decade, so that now about a
million new diesel engines are put to work in the U.S. every year.
Unfortunately, these diesel engines emit large quantities of harmful
pollutants annually.
Furthermore, although diesel emissions in this country come mostly
from heavy-duty trucks and nonroad equipment, an additional source may
grow out of auto manufacturers' plans to greatly increase the sales of
diesel-powered light-duty vehicles (LDVs) and especially of light-duty
trucks (LDTs), a category that includes the fast-selling sport-utility
vehicles, minivans, and pickup trucks. These plans reflect the
continuation of an ongoing dieselization trend, a trend recently most
evident in the growing popularity of diesel-powered light heavy-duty
trucks (8500 to 19,500 pounds). Diesel market penetration is working
its way from larger to smaller highway applications and to a broader
array of nonroad equipment applications. Finally, especially in Europe
where diesels have

[[Page 35437]]

already gained a broad consumer acceptance, the diesel engine is
increasingly viewed as an attractive technology option for reducing
emissions of gases that contribute to global warming, because it has
greater operating efficiency than a gasoline engine.
2. Past Progress and New Developments
Since the 1970's, highway diesel engine designers have employed
numerous strategies to meet our emissions standards, beginning with
smoke controls, and focusing in the 1990's on increasingly stringent
NO_X, hydrocarbon, and PM standards. These strategies have
generally focused on reducing engine-out emissions and not on exhaust
emission controls, although low-efficiency oxidation catalysts have
been applied in some designs to reduce PM (and even their effectiveness
has been limited by sulfur in the fuel). On the fuel side, we set
quality standards that provided emissions benefits by limiting the
amount of sulfur and aromatics in highway diesel fuel beginning in 1993
(55 FR 34120, August 21, 1990). Our most recent round of standard
setting for heavy-duty highway diesels occurred in 1997 (62 FR 54693,
October 21, 1997), effective with the 2004 model year. These standards
were recently reviewed in a proposed rulemaking (64 FR 58472, October
29, 1999), which proposed to confirm them. These actions will result in
engines that emit only a fraction of the NO_X, hydrocarbons,
and PM produced by engines manufactured just a decade ago. We consider
this an important first phase of our current initiative to reconcile
the diesel engine with the environment.
Nevertheless, certain characteristics inherent in the way diesel
fuel combustion occurs have prevented achievement of emission levels
comparable to those of today's gasoline-fueled vehicles. Although
diesel engines provide advantages in terms of fuel economy, durability,
and evaporative emissions, and have inherently low exhaust emissions of
hydrocarbons and carbon monoxide, controlling NO_X emissions
is a greater challenge for diesel engines than for gasoline engines,
primarily because of the ineffectiveness of three-way catalysis in the
oxygen-rich and relatively cool diesel exhaust environment. Similarly,
PM emissions, which are inherently low for properly operating gasoline
engines, are more difficult to control in diesel engines, because the
diesel combustion process tends to form soot particles. The challenge
is somewhat complicated by the fact that historical diesel
NO_X control approaches tend to increase PM, and vice versa,
but both are harmful pollutants that need to be controlled.
Considering the air quality impacts of diesel engines and the
potential for growth of diesels in the lighter-duty portion of the
market, it is imperative that progress in diesel emissions control
continue. Fortunately, encouraging progress is now being made in the
design of exhaust emission control devices for diesel applications,
driven in part by the challenge presented by the stringent Tier 2
standards for light-duty vehicles. As discussed in detail in section
III, promising new exhaust emission control technologies for
NO_X, PM, and hydrocarbon reduction show potential for a
major advancement in diesel emissions control of a magnitude comparable
to that ushered in by the automotive catalytic converter in the 1970's.
However, changes in diesel fuel quality will be needed to enable these
high-efficiency exhaust emission control devices. With these promising
technologies, diesel vehicles have potential to achieve gasoline-like
exhaust emission levels, in addition to their inherent advantages over
gasoline vehicles with respect to fuel economy, lower greenhouse gas
emissions, and lower evaporative hydrocarbon emissions.
3. Tier 2 Emissions Standards
Auto manufacturers' design plans for new light-duty diesel vehicle
models will be greatly affected by our recent adoption of stringent new
emission standards for light-duty highway vehicles (referred to as
``Tier 2'' standards) that will phase in between 2004 and 2009. These
Tier 2 standards will require significant improvements in electronic
engine controls and catalysts on gasoline vehicles. (We anticipate that
these advances will be transferred over to heavy-duty gasoline vehicles
in meeting the standards proposed in this document). The Tier 2
NO_X and PM standards (that apply equally to gasoline and
diesel vehicles) are far more challenging for diesel engine designers
than the most stringent light- or heavy-duty vehicle standards
promulgated to date, and so will require the use of advanced emission
control technologies. However, the low sulfur highway diesel fuel
proposed in this notice would make it possible for designers to employ
advanced exhaust emission control technologies in these light-duty
applications, and the timing of the proposed fuel change provides for
the use of these devices in time to satisfy Tier 2 phase-in
requirements.
The Tier 2 program phases in interim and final standards over a
number of years, providing manufacturers the option of delaying some of
their production of final Tier 2 designs until later in the phase-in.
For vehicles up to 6000 lbs GVWR (LDVs) and light light-duty trucks
(LLDTs)), the interim standards begin in 2004 and phase out by 2007, as
they are replaced by the final Tier 2 standards. For vehicles between
6000 and 8500 lbs ( heavy light-duty trucks (HLDTs)), the interim
standards begin in 2004 and phase out by 2009 as they are replaced by
the final Tier 2 standards. A new category of vehicles between 8,500
and 10,000 lbs, medium-duty passenger vehicles (MDPVs), will follow the
same phase-in schedule as HLDTs.
Our assessment in the Tier 2 final rule is that the interim
standards are feasible for diesel vehicles without a need for fuel
quality changes. Manufacturers can take advantage of the flexibilities
provided in the Tier 2 program to delay the need for light-duty diesels
to meet the final Tier 2 levels until late in the phase-in period (as
late as 2007 for LDVs and LLDTs, and 2009 for HLDTs and MDPVs).
However, low sulfur fuel is expected to be needed for diesel vehicles
designed to meet the final NO_X and PM standards, because
these vehicles are likely to employ light-duty versions of the sulfur-
sensitive exhaust emission control technologies discussed in Section
III. The gasoline quality changes and light-duty gasoline engine
developments that will result from the Tier 2 rule would also help make
it feasible for heavy-duty gasoline engines to meet the standards
proposed in this document.
4. Mobile Source Air Toxics Rulemaking
Passenger cars, on-highway trucks, and nonroad equipment emit
hundreds of different compounds and elements. Several of these are
considered to be known, likely, or possible human carcinogens. These
include diesel exhaust, plus several VOCs such as acetaldehyde,
benzene, 1,3-butadiene, formaldehyde, and acrolein. Trace metals may
also be present in heavy-duty diesel engine emissions, resulting from
metals in fuels and lubricating oil, and from engine wear. Several of
these metals have carcinogenic and mutagenic effects.
These and other mobile source air toxics are already controlled
under existing programs established under Clean Air Act sections 202(a)
(on-highway engine requirements), 211 (the fuel requirements), and 213
(nonroad engine requirements). Although these programs are primarily
designed for control of criteria pollutants, especially ozone and
PM10, they also achieve

[[Page 35438]]

important reductions in air toxics through VOC and hydrocarbon
controls.
In addition to these programs, section 202(l)(2) of the Act directs
us to consider additional controls to reduce emissions of hazardous air
pollutants from motor vehicles, their fuels, or both. Those standards
are to reflect the greatest degree of emission reduction achievable
through the application of technology which will be available, taking
into account existing standards, costs, noise, energy, and safety
factors. We anticipate that this section 202(l)(2) rulemaking, which we
expect to propose in July 2000 and finalize in December 2000, will
consist of three parts. First, we will identify a list of hazardous air
pollutants emitted from motor vehicles and determine which of these
endanger human health and welfare. Diesel particulate matter will be
considered as part of this determination because, as discussed in
section II, human epidemiological studies have suggested that diesel
exhaust is associated with increased risk of adverse respiratory
effects and lung cancer. Second, we will consider more comprehensively
the contribution of mobile sources to the nation's air toxics inventory
and evaluate the toxics benefits of existing and proposed emission
control programs. The benefits of the program proposed in today's
action will be included in this analysis. Finally, we will consider
whether additional controls are appropriate at this time, given
technological feasibility, cost, and the other criteria specified in
the Act.
5. Nonroad Engine Standards and Fuel
Although this proposal covers only highway diesel engines and fuel,
it is clear that potential requirements for nonroad diesel engines and
fuel are related. It is expected that nonroad diesel fuel quality,
currently unregulated, may need to be controlled in the future in order
to reduce the large contribution of nonroad engines to NO_X
and PM inventories. Refiners, fuel distributors, states, environmental
organizations, and others have asked that we provide as much
information as possible about the future specifications for both types
of fuel as early as possible.
We do plan to give further consideration to further control of
nonroad engine emissions. As discussed below in section IX, an
effective control program for these engines requires the resolution of
several major issues relating to engine emission control technologies
and how they are affected by fuel sulfur content. The many issues
connected with any rulemaking for nonroad engines and fuel warrant
serious attention, and we believe it would be premature today for us to
attempt to propose resolutions to them. We plan to initiate action in
the future to formulate thoughtful proposals covering both nonroad
diesel fuel and engines.
6. Actions in California
The California Air Resources Board (ARB) and local air quality
management districts within California are also pursuing measures to
better control diesel emissions. Key among these efforts is work
resulting from the Board's designation of particulate emissions from
diesel-fueled engines as a toxic air contaminant (TAC) on August 27,
1998. TACs are air pollutants that may cause or contribute to an
increase in death or serious illness or may pose a present or future
hazard to human health. The TAC designation was based on research
studies showing that emissions from diesel-fueled engines may cause
cancer in animals and humans, and that workers exposed to higher levels
of emissions from diesel-fueled engines are more likely to develop lung
cancer.
The ARB has now begun a public process to evaluate the need to
further reduce the public's exposure to organic gases and PM emissions
from diesel-fueled engines, and the feasibility and cost of doing
so.\4\ This evaluation is being done in consultation with the local air
districts, affected industries, and the public, and will result in a
report on the appropriate degree of control. Based on this report, if
cost effective measures are identified that will reduce public
exposure, then specific control measures applicable in California will
be developed in a public process.
---------------------------------------------------------------------------

\4\ Regularly updated information on this effort can be obtained
at a website maintained by the ARB staff: www.arb.ca.gov/toxics/
diesel/diesel.htm
---------------------------------------------------------------------------

The ARB also recently adopted stringent new emission requirements
for urban transit buses and is considering similar requirements for
school buses.\5\ This program is aimed at encouraging the use of clean
alternative fuels and high-efficiency diesel emission control
technologies. Their program includes requirements for zero-emissions
buses, fleet average NO_X levels, and retrofits for PM
control, as well as model year 2007 NO_X and PM standards
levels of 0.2 and 0.01 g/bhp-hr, respectively (equal to the levels
proposed in this document). It also requires that all diesel fuel used
by transit agencies after July 1, 2002 must meet a cap of 15 ppm
sulfur. This is the same as the sulfur level proposed in this document,
but in batch amounts and on a much earlier schedule to support the
ARB's proposed PM retrofit schedule.
---------------------------------------------------------------------------

\5\ ``Notice of Public Hearing To Consider the Adoption of a
Public Transit Bus Fleet Rule and Emission Standards For New Urban
Buses'', California ARB, November 30, 1999, and ARB Resolution 00-2,
dated February 24, 2000.
---------------------------------------------------------------------------

California's urban bus program is focused on only a portion of the
highway diesel fleet and fuel, characterized by short-range trips and
captive fuel supplies. The large amount of interstate truck traffic in
California and the fact that these trucks can travel many miles between
refuelings would dramatically reduce the effectiveness of a more
comprehensive State program, and would also subject California
businesses to competitive disadvantages. As a result, the ARB has
stressed the need for action at a Federal level, and is depending on
our efforts to control HDV NO_X and PM emissions and to
regulate diesel fuel. We agree that a national program is appropriate
to ensure the effectiveness of such a program.
7. Retrofit Programs
Many States facing air quality improvement challenges have
expressed strong interest in programs that would reduce emissions from
existing highway and nonroad diesel engines through the retrofitting of
these engines with improved emission control devices. The urban bus
program proposed by the California ARB includes such a retrofit
requirement as one of its major components (see section I.C.6). These
retrofit programs are appealing because the slow turnover of the diesel
fleet to the new low-emitting engines makes it difficult to achieve
near-term air quality goals through new engine programs alone. Some of
the exhaust emission control technologies discussed in this proposal
are especially appealing for use in retrofits because they can be
fitted to an existing vehicle as add-on devices without major engine
modifications, although some of the more sophisticated systems that
require careful control of engine parameters may be more challenging.
Because of the uncertainty at this time in how and when such
programs may be implemented, this proposal does not calculate any
benefits from them. Nevertheless, we believe that this proposed program
can enable the viability of these retrofit technologies. We expect that
large emission benefits from the existing fleet could be realized as a
result of the fuel changes we are proposing here, combined with
retrofit versions of the technologies that would be developed in
response to the proposed engine standards. These

[[Page 35439]]

benefits would be especially important in the early years of the
program when new vehicles standards are just beginning to have an
impact, and when States and local areas need to gain large reductions
to attain air quality goals.
8. Actions in Other Countries
There is substantial activity taking place in many countries of the
world related to the regulation of diesel fuel and engines. The large
light-duty vehicle market share enjoyed by diesels in many European
countries has helped to stir innovation in dealing with diesel
emissions problems. Advanced emissions control technologies are being
evaluated there in the in-use fleet and experience gained from these
trials is helping to inform the diesel emissions control discussion in
the U.S. In addition, several European countries have low sulfur diesel
fuel, with maximum sulfur levels varying from 10 to 50 ppm, and so
experience gained from the use of these fuels, though not completely
transferable to the U.S. situation, also helps to inform the
discussion. European Union countries will limit sulfur in diesel fuel
to 50 ppm by 2005, and even more aggressive plans are being discussed
or implemented. The United Kingdom made a rapid conversion to 50 ppm
maximum sulfur diesel fuel last year by offering tax incentives. This
change occurred with much smaller refinery investments than had been
predicted, and some refinery production there is actually at levels
well below the 50 ppm cap. Germany is moving forward with plans to
introduce a 10 ppm sulfur cap for diesel fuel by 2003, also via tax
incentives, and is attempting to get the 50 ppm specification that was
adopted by the European Commission revised downward to the 10 ppm cap
level.
One European country has had extensive experience with the
transition to low sulfur diesel fuel. In the early 1990's, Sweden
decided to take advantage of the environmental benefits of 10 ppm
sulfur/low aromatics fuel by introducing it with a reduction in the
diesel fuel tax. The program has been quite successful, and in excess
of 90 percent of the road fuel used there is of this 10 ppm maximum
sulfur class.\6\ The ability of the Swedish fuel distributors to
maintain these low sulfur levels at the fuel stations has also been
quite good.
---------------------------------------------------------------------------

\6\ Memo from Thomas M. Baines to Docket A-99-06, October 29,
1999, Docket #A-99-06, Item II-G-12.
---------------------------------------------------------------------------

Section VII.H discusses how differences between the future fuel
specifications in the U.S. and those in Canada and Mexico may affect
the emissions control program proposed in this document.

II. The Air Quality Need and Projected Benefits

A. Overview

Heavy-duty vehicle emissions contribute to air pollution with a
wide range of adverse health and welfare impacts. Emissions of VOC, CO,
NO_X, SO_X, and PM from HD vehicles contribute a
substantial percentage to ambient concentrations of ozone, PM, sulfur
and nitrogen compounds, aldehydes, and substances known or considered
likely to be carcinogens. VOC and diesel PM emissions include some
specific substances known or suspected to cause cancer, and diesel
exhaust emissions are associated with non-cancer health effects. These
ambient concentrations in turn cause human health effects and many
welfare effects including visibility reductions, acid rain,
nitrification and eutrophication of water bodies.
Emissions from heavy-duty vehicles, which are predominantly diesel-
powered, account for substantial portions of the country's ambient PM
and ground-level ozone levels. (NO_X is a key precursor to
ozone formation). By 2007, we estimate that heavy-duty vehicles would
account for 29 percent of mobile source NO_X emissions, and
14 percent of mobile source PM emissions. These proportions are even
higher in some urban areas, such as New York and Los Angeles. Urban
areas, which include many poorer neighborhoods, can be
disproportionately impacted by HDV emissions because of heavy traffic
in and out of densely populated urban areas. Of particular concern is
human epidemiological evidence linking diesel exhaust to an increased
risk of lung cancer. Based on information provided in the draft Health
Assessment Document for Diesel Emissions \7\ and other sources of
information, we believe that emissions from heavy-duty diesel vehicles
contribute to air pollution that warrants regulatory attention under
section 202(a)(3) of the Act.
---------------------------------------------------------------------------

\7\ EPA is revising this draft document in response to comments
by the CASAC.
---------------------------------------------------------------------------

Thirty-six metropolitan areas with a total population of 111
million people have recently violated or are currently violating the 1-
hour ozone NAAQS, and have ozone modeling or other factors which
indicate a risk of NAAQS violations in 2007 or beyond. Another six
areas with 11 million people have recently experienced ozone
concentrations within 10 percent of exceeding the NAAQS between 1996
and 1998 and have some evidence of a risk of future violations. Ten
PM10 nonattainment areas with 27 million people face a
significant risk of experiencing particulate matter levels that violate
the PM10 standard during the time period when this proposal
would take effect. Without reductions from these proposed standards,
there is a significant risk that an appreciable number of these areas
would violate the 1-hour ozone and PM10 standards during the
time period when these proposed standards would apply to heavy-duty
vehicles. Under the mandates and authorities in the Clean Air Act,
federal, State, and local governments are working to bring ozone and
particulate levels into compliance with the 1-hour ozone and
PM10 NAAQS through SIP attainment and maintenance plans, and
to ensure that future air quality continues to achieve these health-
based standards. The reductions proposed in this rulemaking would
assist these efforts.
The proposed heavy-duty vehicle and engine emission standards,
along with the diesel fuel sulfur standard proposed today, would have a
dramatic impact in reducing the large contribution of HDVs to air
pollution. The proposed standards would result in substantial benefits
to public health and welfare through significant annual reductions in
emissions of NO_X, PM, NMHC, carbon monoxide, sulfur dioxide,
and air toxics. For example, we project a 2 million ton reduction in
NO_X emissions from HD vehicles in 2020, which would increase
to 2.8 million tons in 2030 when the current HD vehicle fleet is
completely replaced with newer HD vehicles that comply with these
proposed emission standards. When coupled with the emission reductions
projected to result from the Phase 1 (model year 2004) HDV standards,
the emission reductions from heavy-duty vehicles are projected to be as
large as the substantial reductions the Agency expects from light-duty
vehicles as a result of its recently promulgated Tier 2 rulemaking.

B. Public Health and Welfare Concerns

The following subsections present the available information on the
air pollution situation that is likely to exist without this rule for
each ambient pollutant. We also present information on the improvement
that would result from this rule. The Agency's analysis and this
proposal are supported by the numerous letters received from States and
environmental organizations calling for significant emission reductions
from heavy-duty vehicles in order to enable

[[Page 35440]]

these areas to achieve and sustain clean, healthful air.\8\
---------------------------------------------------------------------------

\8\ Letters from States and environmental organizations are
located in the docket for this proposal.
---------------------------------------------------------------------------

1. Ozone and Its Precursors

a. Health and Welfare Effects From Short-Term Exposures to Ozone

NO_X and VOC are precursors in the photochemical reaction
which forms tropospheric ozone. A large body of evidence shows that
ozone can cause harmful respiratory effects including chest pain,
coughing, and shortness of breath, which affect people with compromised
respiratory systems most severely. When inhaled, ozone can cause acute
respiratory problems; aggravate asthma; cause significant temporary
decreases in lung function of 15 to over 20 percent in some healthy
adults; cause inflammation of lung tissue; may increase hospital
admissions and emergency room visits; and impair the body's immune
system defenses, making people more susceptible to respiratory
illnesses. Children and outdoor workers are likely to be exposed to
elevated ambient levels of ozone during exercise and, therefore, are at
greater risk of experiencing adverse health effects. Beyond its human
health effects, ozone has been shown to injure plants, reducing crop
yields.

b. Current and Future Nonattainment Status With the 1-Hour Ozone NAAQS

Exposure to levels of ozone that are not in compliance with the 1-
hour ozone NAAQS are a serious public health and welfare concern. The
following sections discuss the present situation and outlook regarding
attainment in areas of the country where ozone levels presently fail to
comply with this NAAQS, or where they have come close to failing to
comply in recent years.
Over the last decade, emissions have declined and national air
quality has improved for all six criteria pollutants, including
ozone.\9\ Some of the greatest emissions reductions have taken place in
densely-populated urban areas, where emissions are heavily influenced
by mobile sources such as cars and trucks. For example, VOC and
NO_X emissions in several urban areas in the Northeast
declined by 15 percent and 14 percent from 1990 to 1996.\10\ However,
when ozone trends are normalized for annual weather variations between
1989 and 1998, they reveal a downward trend in the early 1990's
followed by a leveling off, or an upturn in ozone levels, over the past
several years in many urban areas.\11\
---------------------------------------------------------------------------

\9\ National Air Quality and Emissions Trends Report, 1997, US
EPA, December 1998.
\10\ National Emissions Trends database.
\11\ Trends in Daily Maximum 1-hour Ozone in Selected Urban
Areas, 1989-1998.
---------------------------------------------------------------------------

Despite impressive improvements in air quality over the last
decade, present concentrations of ground-level ozone continue to
endanger public health and welfare in many areas. As of December, 1999,
92 million people (1990 census) lived in 32 metropolitan areas
designated nonattainment under the 1-hour ozone NAAQS.\12\ In addition,
there are 14 areas with a 1996 population of 17 million people not
currently listed as non-attainment areas because the 1-hour ozone
standard was revoked for these areas (we have proposed to re-instate
the standard).\13\ These 14 areas are relevant to this proposal because
ozone concentrations above the health-based ozone standard, should they
occur, endanger public health and welfare independent of the
applicability of the 1-hour standard or an area's official attainment
or nonattainment status. Ozone also has negative environmental impacts.
For example, exposure of vegetation to ozone can inhibit
photosynthesis, and alter carbohydrate allocation, which in turn can
suppress the growth of crops, trees, shrubs and other plants.
---------------------------------------------------------------------------

\12\ Memorandum to Air Docket, January 12, 2000. Information on
ozone nonattainment areas and population as of December 13, 1999
from US EPA website www.epa.gov/airs/nonattn.html, USA Air Quality
Nonattainment Areas, Office of Air Quality Planning and Standards.
The reader should note that the 32 areas mentioned here are
designated nonattainment areas, while the 36 areas noted in the
overview section have recent (1995-1998) or current violations, and
predicted exceedances in 2007 or 2030 based on air quality modeling
or other evidence discussed in more detail later in this preamble,
and in the draft RIA.
\13\ 64 FR 57424 (October 25, 1999)
---------------------------------------------------------------------------

The next two sections present lists of metropolitan areas, in two
tables, with potential for violating the ozone standard in the future.
The first section presents a table with 33 metropolitan areas that were
predicted by Tier 2 modeling to have exceedances in either 2007 or
2030, and accompanying text identifies an additional nine areas for
which we have other evidence of a risk of future exceedances. The
second section discusses the air quality prospects for these 42 areas,
which are divided into several groups. These groups are presented in
Table II.B-2.

i. Ozone Predictions Made in the Tier 2 Rulemaking and Other
Information on Ozone Attainment Prospects

In conjunction with its Tier 2 rulemaking efforts, the Agency
performed ozone air quality modeling for nearly the entire Eastern U.S.
covering metropolitan areas from Texas to the Northeast, and for a
western U.S. modeling domain. The ozone modeling we did as part of the
Tier 2 rulemaking predicted that without further emission reductions, a
significant number of areas recently experiencing ozone exceedances
across the nation are at risk of failing to meet the 1-hour ozone NAAQS
in 2007 and beyond, even with Tier 2 and other controls currently in
place.
The general pattern observed from the Tier 2 ozone modeling is a
broad reduction between 1996 and 2007 in the geographic extent of ozone
concentrations above the 1-hour NAAQS, and in the frequency and
severity of exceedances. Despite this improvement from 1996 to 2007,
many ozone exceedances were predicted to occur in 2007 even with
reductions from Tier 2 standards and other controls currently in place,
affecting 33 metropolitan areas across the nation. Assuming no
additional emission reductions beyond those that will be achieved by
current control programs,\14\ a slight decrease below 2007 levels in
modeled concentrations and frequencies of exceedances was predicted for
2030 for most areas. Exceedances were still predicted in 2030 in most
of the areas where they were predicted in 2007.\15\
---------------------------------------------------------------------------

\14\ Current control programs assumed for the predictions
summarized here included the Tier 2/Gasoline Sulfur program and some
specific programs that are legally required but not yet fully
adopted, such as the regional Ozone Transport Rule and not-yet-
adopted MACT standards that will affect VOC emissions.
\15\ Achieving attainment with the ozone standard is only one
measure of air quality improvement. EPA found that the Tier 2
program significantly lowers the model-predicted number of
exceedances of the ozone standard by one tenth in 2007, and by
almost one-third in 2030 across the nation (Tier 2 RIA).
---------------------------------------------------------------------------

Although we did not model ozone concentrations for years between
2007 and 2030, we may expect that they would broadly track the national
emissions trends. Based on these emission trends alone, national ozone
concentrations, on average, would be projected to decline after 2007
largely due to penetration of Tier-2 compliant vehicles into the light
duty vehicle fleet, but begin to increase around 2015 or 2020 due to
economic growth until they reach the 2030 levels just described.
However, the change in ozone levels from the expected NO_X
reduction is relatively small compared to the effects of variations in
ozone due to meteorology. Furthermore, in some areas, where growth
exceeds national averages, emissions levels would begin increasing
sooner and reach higher levels in 2030.

[[Page 35441]]

Table II.B-1 lists the 33 areas with predicted 1-hour ozone
exceedances in 2007 and/or 2030 based on the Tier 2 modeling, after
accounting for the emission reductions from the Tier 2 program and
other controls. \16\ There are areas that are not included in this
table that will be discussed shortly. A factor to consider with respect
to the ozone predictions in Table II.B-1 is that recent improvements to
our estimates of the current and future mobile source NO_X
inventory have resulted in an increase in our estimate of aggregate
NO_X emissions from all sources by more than eight percent
since the air quality modeling performed for the Tier 2 rule. The
adjusted NO_X inventory level in 2015 is greater than the
NO_X inventory used in the Tier 2 air quality analysis for
2030. If we were to repeat the ozone modeling now for the 2015 time
frame, using the new emissions estimates, it would most likely predict
exceedances in 2015 for all the areas that had 2030 exceedances
predicted in the modeling done for the Tier 2 rulemaking. As summarized
in Table II.B-1, the Tier 2 modeling predicted that there will be 33
areas in 2007 or 2030 with about 89 million people predicted to exceed
the 1-hour ozone standard, even after Tier 2 and other controls
currently in place. Additional information on ozone modeling is found
in the draft RIA and the technical support document for the Tier 2
rule, which is in the docket for this rulemaking. We request comment on
the inventory estimates and ozone air quality modeling analysis
described in this proposal.
---------------------------------------------------------------------------

\16\ Table II.B-1 excludes areas for which the Tier 2 modeling
predicted exceedances in 1996 but for which the actual ozone design
values in 1995-1997 and 1996-1998 were both less than 90 percent of
the NAAQS. For these areas, we considered the ozone model's
predictions of 2007 or 2030 exceedances to be too uncertain to play
a supportive role in our rulemaking determinations. Also, 2007 ozone
was not modeled for western areas. For 2030, all areas were modeled
for fewer episode days which, along with a general model under-
prediction bias, may result in an underestimation of 2030
exceedances. Without these factors, there could have been more
western areas listed in Table II.B-1, and more areas with predicted
exceedances in 2030.

Table II.B-1.--Metropolitan Areas With Predicted Exceedances in 2007 or 2030 From Tier 2 Air Quality Modeling
Including Emission Reductions From Tier 2 and Other Current/Committed Controls
----------------------------------------------------------------------------------------------------------------
1996 Population
CMSA/MSAs 2007 Control case 2030 Control case (millions)
----------------------------------------------------------------------------------------------------------------
Boston, MA CMSA........................ X X 5.6
Chicago, IL CMSA....................... X X 8.6
Cincinnati, OH CMSA**.................. X ......................... 1.9
Cleveland, OH CMSA*.................... X X 2.9
Detroit, MI CMSA*...................... X X 5.3
Houston, TX CMSA....................... X X 4.3
Milwaukee, WI CMSA..................... X X 1.6
New York City, NY CMSA................. X X 19.9
Philadelphia, PA CMSA.................. X X 6.0
Washington,-Baltimore, DC-VA-WV-MD CMSA X X 7.2
Atlanta, GA MSA........................ X X 3.5
Barnstable, MA MSA..................... X X 0.2
Baton Rouge, LA MSA.................... X X 0.6
Benton Harbor, MI MSA.................. X X 0.2
Biloxi, MS MSA*........................ X X 0.3
Birmingham, AL MSA..................... X X 0.9
Charlotte, NC MSA...................... X X 1.3
Grand Rapids, MI MSA................... X X 1.0
Hartford, CT MSA....................... X X 1.1
Houma, LA MSA.......................... X X 0.2
Huntington, WV MSA..................... X ......................... 0.3
Indianapolis, IN MSA................... X ......................... 1.5
Louisville, KY MSA..................... X X 1.0
Memphis, TN MSA........................ X X 1.1
Nashville, TN MSA...................... X X 1.1
New London, CT MSA..................... X X 1.3
New Orleans, LA MSA*................... X X 0.3
Pensacola, FL MSA*..................... X ......................... 0.4
Pittsburgh, PA MSA..................... X ......................... 2.4
Providence, RI MSA..................... X X 1.1
Richmond, VA MSA....................... X ......................... 0.9
St. Louis, MO MSA...................... X X 2.5
Tampa, FL MSA*......................... X X 2.2
33 areas / 88.7 million people......... 32 areas/86.3 million 28 areas/83.7 million .................
people people
----------------------------------------------------------------------------------------------------------------
* These areas have registered recent (1995-1998) ozone levels within 10% of the 1-hour ozone standard.
** Based on more recent air quality monitoring data not considered in the Tier 2 analysis, and on 10-year
emissions projections, we expect to redesignate Cincinnati-Hamilton to attainment soon.

Ozone modeling for the Tier 2 rulemaking did not look at the effect
on ozone attainment and maintenance beyond current/committed controls
and the Tier 2/Gasoline Sulfur Program itself. Therefore, Table II.B-1
should be interpreted as indicating what areas are at risk of ozone
violations in 2007 or 2030 without federal or state measures that may
be adopted and implemented after this rulemaking is proposed. We expect
many of the areas listed in Table

[[Page 35442]]

II.B-1 to adopt additional emission reduction programs, but the Agency
is unable to quantify the future reductions from additional State
programs since they have not yet been adopted.
In addition, Table II.B-1 reflects only the ozone predictions made
in the modeling for the Tier 2 rulemaking. The Tier 2 modeling did not
predict (or did not provide information regarding) 2007 or 2030
violations for a number of areas for which other available ozone
modeling has shown 2007 violations, or for which the history and
current degree of nonattainment indicates some risk of ozone violations
in 2007 or beyond. These nine areas had a 1996 population of 30 million
people. They include seven ozone nonattainment areas in California (Los
Angeles, San Diego, Southeast Desert, Sacramento, Ventura County, San
Joaquin Valley, and San Francisco), and two Texas areas (Beaumont-Port
Arthur and Dallas). A more detailed discussion is presented in the
Draft RIA. The following section will discuss the air quality prospects
of these 42 areas (i.e., the 33 shown in Table II.B-1, plus the nine
additional areas identified in this paragraph).
For the final rule, the Agency plans to use the same modeling
system as was used in its Tier 2 air quality analysis with updated
inventory estimates for 2030 and a further characterization of the
inventory estimates for the interim period between 2007 and 2030 We
plan to release the products of these revised analyses into the public
record on a continuous basis as they are developed. Interested parties
should check docket number A-99-06 periodically for updates.

ii. Areas At Risk of Exceeding the 1-Hour Ozone Standard

This section presents the Agency's conclusions about the risk of
future nonattainment for the 42 areas identified above. These areas are
listed in Table II.B-2, and are subdivided into three groups. The
following discussion follows the groupings from top to bottom. A more
detailed discussion is found in the Draft RIA.
In general, EPA believes that the proposed new standards for heavy-
duty vehicles are warranted by a sufficient risk that without these
standards, some areas would experience violations of the 1-hour NAAQS
at some time during the period when this rulemaking would achieve its
emission reductions, despite efforts that EPA, States and localities
are now making through SIPs to reach attainment and to preserve
attainment by developing and implementing maintenance plans. Because
ozone concentrations causing violations of the 1-hour ozone standard
are well established to endanger public health and welfare, this
indicates that it is appropriate for the Agency to propose setting new
standards for heavy-duty vehicles.
Our belief regarding the risk of future violations of the 1-hour
NAAQS is based upon our consideration of predictive ozone air quality
modeling and analysis we performed for U.S. metropolitan areas for the
recent Tier 2 rulemaking, and the predictive ozone modeling and other
information that has come to us through the SIP process, and other
local air quality modeling for certain areas. We have assessed this
information in light of our understanding of the factors that influence
ozone concentrations, taking due consideration of current and future
federal, state and local efforts to achieve and maintain the ozone
standard through air quality planning and implementation.
Ten metropolitan areas that fall within ozone nonattainment areas
have statutorily-defined attainment dates of 2007 or 2010, or have
requested attainment date extensions to 2007 (including two requests on
which we have not yet proposed any action). These 10 areas are listed
at the top of Table II.B-2, and are New York City, Houston, Hartford,
New London, Chicago, Milwaukee, Dallas, Beaumont-Port Arthur, Los
Angeles, and Southeast Desert. The Los Angeles (South Coast Air Basin)
ozone attainment demonstration is fully approved, but it is based in
part on reductions from new technology measures and actions that have
yet to be identified. Accordingly, the State will be able to benefit
from, and will need, the reductions from this proposed rule in order to
meet the NO_X and VOC shortfalls identified in the South
Coast Air Basin's SIP. The 2007 attainment demonstration for the
Southeast Desert area is also approved. However, because ozone travels
from the South Coast to the Southeast Desert, attainment in the
Southeast Desert may depend on progress in reducing ozone levels in the
South Coast Air Basin.
The process of developing adequate attainment plans has been
difficult. While the efforts by EPA and the States have been more
prolonged than expected, they are nearing completion. Of the remaining
eight areas discussed above, two--Chicago and Milwaukee--do not have
EPA-identified shortfalls in their 1998 attainment demonstrations.
However, these two areas are revising their local ozone air quality
modeling, which will be taken into account in the final rule. We have
recently proposed to approve attainment plans for New York, Houston,
Hartford and New London, and we hope to receive attainment plans and
propose such approval soon for Dallas and Beaumont-Port Arthur. EPA has
proposed, or expects to propose, that attainment in 2007 in each of
these six areas depends upon either achieving specified additional
emission reductions in the area itself, or achieving ozone reductions
in an upwind nonattainment area that has such a shortfall. Those areas
with shortfalls will be able to take credit for the expected reductions
from the proposed rule in their attainment demonstrations, once the
rule is promulgated. We expect to rely in part on these reductions in
reaching our final conclusion as to whether each of the eight areas for
which we have reviewed an attainment demonstration, or expect to review
an attainment demonstration soon, is more likely than not to attain on
its respective date, whether or not the State formally relies on these
reductions as part of its strategy to fill the identified shortfall in
its attainment demonstration, if any.
The proposed new standards for heavy-duty vehicles would help
address some of the uncertainties and risks that are inherent in
predicting future air quality over a long period. Actual ozone levels
may be affected by increased economic growth, unusually severe weather
conditions, and unexpectedly large changes in vehicle miles traveled.
For example, the emissions and air quality modeling that forms the
basis for the 2007-to-2030 emissions and ozone trend described earlier
used a 1.7 percent national VMT growth rate. Historical growth in
national VMT for LDVs over the last 30 years has averaged 2.7 percent
per year, but over the past 10 years, annual VMT growth has fluctuated
from 1.2 percent to 3.5 percent. The growth rates can also vary from
locality to locality. The reported annual VMT growth rate experienced
in Atlanta, a fast-growing metropolitan area, was six percent from
1986-1997, or more than twice the 30-year national average, and year-
to-year variations in Atlanta's reported annual VMT ranged from a 12%
increase to no increase over the same period. While some factors
influencing previous VMT growth rates, such as increased participation
of women in the workforce, may be declining, other factors, such as
widening suburbanization, more suburb-to-suburb commuting and the rise
of healthier and wealthier older age drivers, may result in increased
VMT growth rates.\17\ Activity by other source

[[Page 35443]]

types also varies due to economic factors. Actual future VMT and other
economic growth in specific areas may vary from the best predictions
that have been used in each attainment demonstration. Over a number of
years, differences in annual growth can cause substantial differences
in total emissions. These uncertainties, and others, dictate that a
prudent course for the Agency is to protect public health by increasing
our confidence that the necessary reductions will be in place. This
proposed rulemaking would provide significant and needed reductions to
those areas at risk of violating the 1-hour ozone standard during the
time period when this rule would take effect.
---------------------------------------------------------------------------

\17\ See Tier 2 Response to Comments document for a longer
decision.
---------------------------------------------------------------------------

The reductions from this proposal would begin in 2007 and would
continue to grow over time as the existing heavy-duty fleet is replaced
by newer vehicles meeting the proposed emission standards. Even
assuming attainment is achieved, areas that wish a redesignation to
attainment may rely on further reductions generated by this rulemaking
to support their 10-year maintenance plan. Even if an area does not
choose to seek redesignation, the continuing reductions from this
proposed rulemaking would help ensure maintenance with the 1-hour
standard after attainment is reached.
Thus, a total of six metropolitan areas need additional measures to
meet the shortfalls in the applicable attainment demonstrations, or are
subject to ozone transport from an upwind area that has an identified
shortfall. In addition, two areas are expected to need additional
emission reductions to demonstrate attainment in future SIPs. EPA
believes that the States responsible may need, among other reductions,
the level of reductions provided by this rule in order to fill the
shortfalls. We expect to rely in part on these reductions in reaching
our final conclusion as to whether each of the eight areas for which we
have reviewed an attainment demonstration is more likely than not to
attain on its respective date, whether or not the State formally relies
on these reductions as part of its strategy to fill the identified
shortfall in its attainment demonstration. As to all ten areas, even if
all shortfalls were filled by the States, there is some risk that at
least some of the areas will not attain the standards by their
attainment dates of 2007, or 2010 for Los Angeles. In that event, the
reductions associated with this proposed program, which increase
substantially after 2007, would help assure that any residual failures
to attain are remedied. Finally, there is also some risk that the areas
will be unable to maintain attainment after 2007. Considered
collectively, there is a significant risk that some areas would not be
in attainment throughout the period when the proposed rule would reduce
heavy-duty vehicle emissions.
The next group of 26 areas have required attainment dates prior to
2007, or have no attainment date but are subject to a general
obligation to have a SIP that provides for attainment and maintenance.
EPA and the States are pursuing the established statutory processes for
attaining and maintaining the ozone standard where it presently
applies. EPA has also proposed to re-apply the ozone standard to the
remaining areas. The Agency believes that there is a significant risk
that future air quality in a number of these areas would exceed the
ozone standard at some time in the 2007 and later period. This belief
is based on three factors: (1) Recent exceedances in 1995-1997 or 1996-
1998, (2) predicted exceedances in 2007 or 2030 after accounting for
reductions from Tier 2 and other local or regional controls currently
in place or required, and (3) our assessment of the magnitude of recent
violations, the variability of meteorological conditions, transport
from areas with later attainment dates, and other variables inherent in
predicting future attainment such as the potential for some areas to
experience unexpectedly high economic growth rates, growth in vehicle
miles traveled, varying population growth from area to area, and
differences in vehicle choice.
Only a subset of these areas have yet adopted specific control
measures that have allowed the Agency to fully approve an attainment
plan. For some of these areas, we have proposed a finding, based on all
the available evidence, that the area will attain on its attainment
date. In one case, we have proposed that an area will maintain over the
required 10-year time period. However, in many cases, these proposals
depend on the State adopting additional emission reduction measures.
The draft RIA provides more information on our recent proposals on
attainment demonstrations and maintenance plans.\18\ Until the SIPs for
these areas are actually submitted, reviewed and approved, there is
some risk that these areas will not adopt fully approvable SIPs.
Furthermore, some of these areas are not under a current requirement to
obtain EPA approval for an attainment plan. The mechanisms to get to
attainment in areas without a requirement to submit an attainment
demonstration are less automatic, and more uncertain. Even with
suitable plans, implementation success is uncertain, and therefore
there is some risk that 2007 attainment, or maintenance thereafter,
would not happen.
---------------------------------------------------------------------------

\18\ We have recently proposed favorable action, in some cases
with a condition that more emission reductions be obtained, on
attainment demonstrations in these areas with attainment dates prior
to 2007: Philadelphia, Washington-Baltimore, Atlanta, and St. Louis.
We expect to give final approval soon to a maintenance plan and
redesignation to attainment for Cincinnati.
---------------------------------------------------------------------------

Finally, there are six additional metropolitan areas, with another
11.4 million people in 1996, for which the available ozone modeling and
other evidence is less clear regarding the need for additional
reductions. These areas include Biloxi-Gulfport-Pascagoula, MS,
Cleveland-Akron, OH, Detroit-Ann Arbor-Flint, MI, New Orleans, LA,
Pensacola, FL, and Tampa, FL. Our own ozone modeling predicted these
six areas to need further reductions to avoid exceedances in 2007 or
2030. The recent air quality monitoring data for these six areas shows
ozone levels with less than a 10 percent margin below the NAAQS. This
suggests that ozone concentrations in these areas may remain below the
NAAQS for some time, but we believe there is still a risk of that
future ozone levels will be above the NAAQS because meteorological
conditions may be more severe in the future.
In sum, without these reductions, there is a significant risk that
an appreciable number of the 42 areas, with a population of 123 million
people in 1996, will violate the 1-hour ozone standard during the time
period when these proposed standards will apply to heavy-duty vehicles.
The 42 areas consist of the 27 areas with predicted exceedances in 2007
or 2030 under Tier 2 air quality modeling and recent violations of the
1-hour ozone standard, plus seven California areas (South Coast Air
Basin, San Diego, Ventura County, Southeast Desert, San Francisco, San
Joaquin Valley, Sacramento), two Texas areas (Dallas and Beaumont-Port
Arthur), and six areas that have recent ozone concentrations within 10%
of exceeding the standard and predicted exceedances. Additional
information about these areas is provided in the draft RIA.

iii. Conclusion

We have reviewed the air quality situation of three broad groups of
areas: (1) Those areas with recent violations of the ozone standard and
attainment dates in 2007 or 2010, (2) those areas with recent
violations and attainment dates (if any) prior to 2007, and (3) those
areas with recent ozone concentrations within 10% of a violation of the
1-hour ozone

[[Page 35444]]

standard, with predicted exceedances, and without proposed or approved
SIP attainment demonstrations. In general, the evidence summarized in
this section, and presented in more detail in the draft RIA, supports
the Agency's belief that emissions of NO_X and VOC from
heavy-duty vehicles in 2007 and later will contribute to a national
ozone air pollution problem that warrants regulatory attention under
section 202(a)(3) of the Act.

Table II.B-2
------------------------------------------------------------------------
Proposed
Metropolitan area/State reinstatement of 1996 population
ozone standard (in millions)
------------------------------------------------------------------------
Areas with 2007/2010 Attainment
Dates (Established or
Requested):
New York City, NY-NJ-CT..... 19.9
Houston, TX................. 4.3
Hartford, CT................ 1.1
New London, CT.............. 1.3
Chicago, IL-IN.............. 8.6
Milwaukee, WI............... 1.6
Dallas, TX.................. 4.6
Beaumont-Port Arthur, TX.... 0.4
Los Angeles, CA............. 15.5
Southeast Desert, CA........ 0.4
Subtotal of 10 areas...... 57.7
Areas with Pre-2007 Attainment
Dates or No Specific Attainment
Date, with a Recent History of
Nonattainment:**
Atlanta, GA................. 3.5
Philadelphia-Wilmington- 6.0
Atlantic City, PA-NJ-DE-MD.
Sacramento, CA.............. 1.5
San Joaquin Valley, CA 2.7
*possible future
reclassification and change
of attainment date to 2005.
Ventura County, CA.......... 0.7
Washington-Baltimore, DC-MD- 7.2
VA-WV......................
Charlotte-Gastonia, NC...... X 1.3
Grand Rapids, MI............ X 1.0
Huntington-Ashland, WV-KY... X 0.3
Indianapolis, IN............ X 1.5
Memphis, TN................. X 1.1
Nashville, TN............... X 1.1
Barnstable-Yarmouth, MA..... X 0.2
Boston-Worcester-Lawrence, X 5.6
MA.........................
Houma, LA................... X 0.2
Providence-Fall River- X 1.1
Warwick, RI-MA.............
Richmond-Petersburg, VA..... X 1.0
Benton Harbor, MI........... X 0.2
Baton Rouge, LA............. 0.6
Birmingham, AL.............. 0.9
Cincinnati-Hamilton, OH-KY- 1.9
IN*........................
Louisville, KY-IN........... 0.3
Pittsburgh, PA MSA.......... 2.4
San Diego, CA............... 2.8
San Francisco Bay Area, CA.. 6.2
St. Louis, MO-IL............ 2.5
Subtotal of 26 areas...... 53.8
Areas with Pre-2007 Attainment
Dates and Recent Concentrations
within 10% of an Exceedance,
But With No Recent History of
Nonattainment:
Biloxi-Gulfport-Pascagoula, X 0.3
MS MSA.....................
Cleveland-Akron, OH CMSA.... X 2.9
Detroit-Ann Arbor-Flint, MI X 5.3
CMSA.......................
New Orleans, LA MSA......... X 0.3
Pensacola, FL MSA........... X 0.4
Tampa, FL MSA............... X 2.2
Subtotal of 6 areas....... 11.4
Total 1996 Population of All
Areas at Risk of Exceeding the
Ozone Standard in 2007 or
Thereafter:
42 Areas--total population.. 122.9
------------------------------------------------------------------------
*Based on more recent air quality monitoring data not considered in the
Tier 2 analysis, and on 10-year emissions projections, we expect to
redesignate Cincinnati-Hamilton to attainment soon.
**The list includes certain areas that are currently not violating the 1-
hour NAAQS.

c. Public Health and Welfare Concerns From Prolonged and Repeated
Exposures to Ozone

A large body of scientific literature regarding health and welfare
effects of ozone has associated health effects with certain patterns of
ozone exposures that do not include any hourly ozone concentration
above the 0.12 parts per million (ppm) level of the 1-hour NAAQS. The
science indicates that there are health effects attributable to
prolonged and repeated exposures to lower ozone concentrations. Studies
of 6 to 8 hour exposures showed health effects from prolonged and
repeated exposures at moderate levels of exertion to ozone
concentrations as low as 0.08

[[Page 35445]]

ppm. Prolonged and repeated ozone concentrations at these levels are
common in areas throughout the country, and are found in areas that are
exceeding, and areas that are not exceeding, the 1-hour ozone standard.
For example, in 1998, almost 62 million people lived in areas with 2 or
more days with concentrations of 0.09 ppm or higher, excluding areas
currently violating the 1-hour NAAQS. Since prolonged exposures at
moderate levels of ozone are more widespread than exceedances of the 1-
hour ozone standard, and given the continuing nature of the 1-hour
ozone problem described above, adverse health effects from this type of
ozone exposure can reasonably be anticipated to occur in the future in
the absence of this rule. Adverse welfare effects can also be
anticipated, primarily from damage to vegetation. See the draft RIA for
further details.
Studies of acute health effects have shown transient pulmonary
function responses, transient respiratory symptoms, effects on exercise
performance, increased airway responsiveness, increased susceptibility
to respiratory infection, increased hospital and emergency room visits,
and transient pulmonary respiratory inflammation. Such acute health
effects have been observed following prolonged exposures at moderate
levels of exertion at concentrations of ozone well below the current
standard of 0.12 ppm. The effects are more pronounced at concentrations
above 0.09 ppm, affecting more subjects or having a greater effect on a
given subject in terms of functional changes or symptoms. A more
detailed discussion may be found in the Draft RIA.
With regard to chronic health effects, the collective data have
many ambiguities, but provide suggestive evidence of chronic effects in
humans. There is a biologically plausible basis for considering the
possibility that repeated inflammation associated with exposure to
ozone over a lifetime, as can occur with prolonged exposure to moderate
ozone levels below peak levels, may result in sufficient damage to
respiratory tissue that individuals later in life may experience a
reduced quality of life, although such relationships remain highly
uncertain.
We believe that the evidence in the Draft RIA regarding the
occurrence of adverse health effects due to prolonged and repeated
exposure to ozone concentrations in the range discussed above, and
regarding the populations that are expected to receive exposures at
these levels, supports a conclusion that emissions of NO_X,
and VOC from heavy-duty vehicles in 2007 and later will be contributing
to a national air pollution problem that warrants regulatory attention
under section 202(a)(3) of the Act.
Ozone has many welfare effects, with damage to plants being of most
concern. Plant damage affects crop yields, forestry production, and
ornamentals. The adverse effect of ozone on forests and other natural
vegetation can in turn cause damage to associated ecosystems, with
additional resulting economic losses. Ozone concentrations of 0.10 ppm
can be phytotoxic to a large number of plant species, and can produce
acute injury and reduced crop yield and biomass production. Ozone
concentrations at or below 0.10 ppm have the potential over a longer
duration of creating chronic stress on vegetation that can result in
reduced plant growth and yield, shifts in competitive advantages in
mixed populations, decreased vigor, and injury from other environmental
stresses. The forestry, crop and other environmental damage from ozone
in times and places where the 1-hour NAAQS is attained adds support to
the Agency's belief that there will be air pollution in 2007 and
thereafter that warrants regulatory attention under section 202(a)(3)
of the Act.
2. Particulate Matter

a. Health and Welfare Effects

i. Particulate Matter Generally

Particulate matter (PM) represents a broad class of chemically and
physically diverse substances. It can be principally characterized as
discrete particles that exist in the condensed (liquid or solid) phase
spanning several orders of magnitude in size. All particles equal to
and less than 10 microns are called PM10. Fine particles can
be generally defined as those particles with an aerodynamic diameter of
2.5 microns or less (also known as PM2.5), and coarse
fraction particles are those particles with an aerodynamic diameter
greater than 2.5 microns, but equal to or less than a nominal 10
microns. The health and environmental effects of PM are strongly
related to the size of the particles.
The emission sources, formation processes, chemical composition,
atmospheric residence times, transport distances and other parameters
of fine and coarse particles are distinct. Fine particles are directly
emitted from combustion sources and are formed secondarily from gaseous
precursors such as sulfur dioxide, nitrogen oxides, or organic
compounds. Fine particles are generally composed of sulfate, nitrate,
chloride and ammonium compounds; organic and elemental carbon; and
metals. Combustion of coal, oil, diesel, gasoline, and wood, as well as
high temperature process sources such as smelters and steel mills,
produce emissions that contribute to fine particle formation. In
contrast, coarse particles are typically mechanically generated by
crushing or grinding and are often dominated by resuspended dusts and
crustal material from paved or unpaved roads or from construction,
farming, and mining activities. Fine particles can remain in the
atmosphere for days to weeks and travel through the atmosphere hundreds
to thousands of kilometers, while coarse particles deposit to the earth
within minutes to hours and within tens of kilometers from the emission
source.
Particulate matter, like ozone, has been linked to a range of
serious respiratory health problems. Scientific studies suggest a
likely causal role of ambient particulate matter (which is attributable
to a number of sources including diesel) in contributing to a series of
health effects. The key health effects categories associated with
ambient particulate matter include premature mortality, aggravation of
respiratory and cardiovascular disease (as indicated by increased
hospital admissions and emergency room visits, school absences, work
loss days, and restricted activity days), aggravated asthma, acute
respiratory symptoms, including aggravated coughing and difficult or
painful breathing, chronic bronchitis, and decreased lung function that
can be experienced as shortness of breath. For additional information
on health effects, see the draft RIA. Both fine and coarse particles
can accumulate in the respiratory system. Exposure to fine particles is
most closely associated with such health effects as premature mortality
or hospital admissions for cardiopulmonary disease. PM also causes
damage to materials and soiling. It is a major cause of substantial
visibility impairment in many parts of the U.S.
Diesel particles are a component of both coarse and fine PM, but
fall mostly in the fine range. Noncancer health effects associated with
exposure to diesel PM overlap with some health effects reported for
ambient PM including respiratory symptoms (cough, labored breathing,
chest tightness, wheezing), and chronic respiratory disease (cough,
phlegm, chronic bronchitis and some evidence for decreases in pulmonary
function).

[[Page 35446]]

ii. Special Considerations for Diesel PM

Primary diesel particles mainly consist of carbonaceous material,
ash (trace metals), and sulfuric acid. Many of these particles exist in
the atmosphere as a carbon core with a coating of organic carbon
compounds, sulfuric acid and ash, sulfuric acid aerosols, or sulfate
particles associated with organic carbon.
Most diesel particles are in the fine and ultrafine size range.
Diesel PM contains small quantities of numerous mutagenic and
carcinogenic compounds. While representing a very small portion (less
than one percent) of the national emissions of metals, and a small
portion of diesel particulate matter (one to five percent), we note
that several trace metals of toxicological significance are also
emitted by diesel engines in small amounts including chromium,
manganese, mercury and nickel. In addition, small amounts of dioxins
have been measured in diesel exhaust, some of which may partition into
the particle phase, though the impact of these emissions on human
health is not clear.
Because the chemical composition of diesel PM includes these
hazardous air pollutants, or air toxics, diesel PM emissions are of
concern to the agency beyond their contribution to general ambient PM.
Moreover, as discussed in detail in the draft RIA, there have been
health studies specific to diesel PM emissions which indicate potential
hazards to human health that appear to be specific to this emissions
source. For chronic exposure, these hazards included respiratory system
toxicity and carcinogenicity. Acute exposure also causes transient
effects (a wide range of physiological symptoms stemming from
irritation and inflammation mostly in the respiratory system) in humans
though they are highly variable depending on individual human
susceptibility.

b. Potential Cancer Effects of Diesel Exhaust

The EPA draft Health Assessment Document for Diesel Emissions
(draft Assessment) is currently being revised based on comments
received from the Clean Air Scientific Advisory Committee (CASAC) of
EPA's Science Advisory Board.\19\ The current EPA position is that
diesel exhaust is a likely human lung carcinogen and that this cancer
hazard exists for occupational and environmental levels of
exposure.\20\
---------------------------------------------------------------------------

\19\ U.S. EPA (1999) Health Assessment Document for Diesel
Emissions: SAB Review Draft. EPA/600/8-90/057D Office of Research
and Development, Washington, DC. The document is available
electronically at www.epa.gov/ncea/diesel.htm.
\20\ The EPA designation of diesel exhaust as a likely human
carcinogen is subject to further comment by CASAC in 2000. The
designation of diesel exhaust as a likely human carcinogen under the
1996 Proposed Guidelines for Carcinogen Risk Assessment is very
similar to the current 1986 Guidelines for Carcinogen Risk
Assessment that designate diesel exhaust as a probable carcinogen
(B-1 carcinogen). The new guidelines, once finalized, will
incorporate a narrative approach to assist the risk manager in the
interpretation of the carcinogen's mode of action, the weight of
evidence, and any risk related exposure-response or protective
exposure recommendations.
---------------------------------------------------------------------------

In evaluating the available research for the draft Assessment, EPA
found that individual epidemiological studies numbering about 30 show
increased lung cancer risks associated with diesel emissions within the
study populations of 20 to 89 percent depending on the study.
Analytical results of pooling the positive study results show that on
average the risks were increased by 33 to 47 percent. Questions remain
about the influence of other factors (e.g., effect of smoking), the
quality of the individual epidemiology studies, exposure levels, and
consequently the precise magnitude of the increased risk of lung
cancer. From a weight of the evidence perspective, EPA believes that
the epidemiology evidence, as well as supporting data from certain
animal and mode of action studies, support the Agency's proposed
conclusion that exposure to diesel exhaust is likely to pose a human
health hazard at occupational exposure levels, as well as to the
general public exposed to typically lower environmental levels of
diesel exhaust.
Risk assessments on epidemiological studies in the peer-reviewed
literature which have attempted to assess the lifetime risk of lung
cancer in workers occupationally exposed to diesel exhaust suggests
that lung cancer risk may range from 10^-4 to
10^-.\21\ \22\ \23\ The Agency recognizes the significant
uncertainties in these studies, and has not used these estimates to
assess the possible cancer unit risk associated with ambient exposure
to diesel exhaust.
---------------------------------------------------------------------------

\21\ California Environmental Protection Agency, Office of
Health Hazard Assessment (CAL-EPA, OEHHA) (1998) Proposed
Identification of Diesel Exhaust as a Toxic Air Contaminant.
Appendix III Part B Health Risk Assessment for Diesel Exhaust. April
22, 1998.
\22\ Steenland, K., Deddens, J., Stayner, L. (1998) Diesel
Exhaust and Lung Cancer in the Trucking Industry: Exposure-Response
Analyses and Risk Assessment. Am. J Indus. Medicine 34:220-228.
\23\ Harris, J.E. (1983) Diesel emissions and Lung Cancer. Risk
Anal. 3:83-100.
---------------------------------------------------------------------------

While available evidence supports EPA's conclusion that diesel
exhaust is a likely human lung carcinogen, and thus is likely to pose a
cancer hazard to humans, the absence of quantitative estimates of the
lung cancer unit risk for diesel exhaust limits our ability to quantify
with confidence the actual magnitude of the cancer risk. In the draft
1999 Assessment, EPA acknowledged these limitations and provided a
discussion of the possible cancer risk consistent with general
occupational epidemiological findings of increased lung cancer risk and
relative exposure ranges in the occupational and environmental
settings. \24\ The Agency believes that the techniques that were used
in the draft Assessment to qualitatively gauge the potential for and
possible magnitude of risk are reasonable. The details of this approach
are provided in the draft RIA.
---------------------------------------------------------------------------

\24\ See Chapter 8.3 and 9.6 of the draft Health Assessment for
Diesel Exhaust. U.S. EPA (1999) Health Assessment Document for
Diesel Emissions: SAB Review Draft. EPA/600/8-90/057D Office of
Research and Development, Washington, D.C. The document is available
electronically at www.epa.gov/ncea/diesel.htm.
---------------------------------------------------------------------------

In the absence of a quantitative unit cancer risk to assess
environmental risk, EPA has considered the relevant epidemiological
studies and principles for their assessment, the risk from occupational
exposure as assessed by others, and relative exposure margins between
occupational and ambient environmental levels of diesel exhaust
exposure. Based on this epidemiological and other information, there is
the potential that upper bounds on environmental cancer risks from
diesel exhaust may exceed 10^-6 and could be as high as
10^-3. \25\ While uncertainty exists in estimating risk, the
likely hazard to humans together with the potential for significant
environmental risks leads the Agency to believe that diesel exhaust
emissions should be reduced in order to protect the public's health. We
believe that this is a prudent measure in light of the designation of
diesel exhaust as a likely human carcinogen, the exposure of almost the
entire population to diesel exhaust, the significant and consistent
finding of an increase in lung cancer risk in workers exposed to diesel
exhaust, and the potential overlap and/or small difference between some
occupational and environmental exposures.
---------------------------------------------------------------------------

\25\ As used in this proposal, environmental risk is defined as
the risk (i.e. a mathematical probability) that lung cancer would be
observed in the population after a lifetime exposure to diesel
exhaust. Exposure levels may be occupational lifetime or
environmental lifetime exposures. A population risk in the magnitude
of 10^-6 translates as the probability of lung cancer
being evidenced in one person in one million over a lifetime
exposure.
---------------------------------------------------------------------------

As discussed in section I.C.6, ``Actions in California'', the
Office of Environmental Health Hazard

[[Page 35447]]

Assessment (OEHHA, California EPA) has identified diesel PM as a toxic
air contaminant. \26\ California is in the process of determining the
need for, and appropriate degree of control measures for diesel PM.
Apart from the EPA draft Assessment and California EPA's actions,
several other agencies and governing bodies have designated diesel
exhaust or diesel PM as a ``potential'' or ``probable'' human
carcinogen. \27\ \28\ \29\ The International Agency for Research on
Cancer (IARC) considers diesel exhaust a ``probable'' human carcinogen
and the National Institutes for Occupational Safety and Health have
classified diesel exhaust a ``potential occupational carcinogen.''
Thus, the concern for the health hazard resulting from diesel exhaust
exposures is widespread.
---------------------------------------------------------------------------

\26\ Office of Environmental Health Hazard Assessment (1998)
Health risk assessment for diesel exhaust, April 1998. California
Environmental Protection Agency, Sacramento, CA.
\27\ National Institute for Occupational Safety and Health
(NIOSH) (1988) Carcinogenic effects of exposure to diesel exhaust.
NIOSH Current Intelligence Bulletin 50. DHHS, Publication No. 88-
116. Centers for Disease Control, Atlanta, GA.
\28\ International Agency for Research on Cancer (1989) Diesel
and gasoline engine exhausts and some nitroarenes, Vol. 46.
Monographs on the evaluation of carcinogenic risks to humans. World
Heath Organization, International Agency for Research on Cancer,
Lyon, France.
\29\ World Health Organization (1996) Diesel fuel and exhaust
emissions: International program on chemical safety. World Health
Organization, Geneva, Switzerland.
---------------------------------------------------------------------------

c. Noncancer Effects of Diesel Exhaust

The noncancer effects of diesel exhaust emissions are also of
concern to the Agency. EPA believes that chronic diesel exhaust
exposure, at sufficient exposure levels, increases the hazard and risk
of an adverse consequence (including respiratory tract irritation/
inflammation and changes in lung function). The draft 1999 Assessment
discussed an existing inhalation reference concentration (RfC) for
chronic effects that EPA intends to revise in the next draft Assessment
in response to CASAC comments. The revised RfC will be reviewed by
CASAC at a future meeting. An RfC provides an estimate of the
continuous human inhalation exposure (including sensitive subgroups)
that is likely to be without an appreciable risk of deleterious
noncancer effects during a lifetime.

d. Attainment and Maintenance of the PM10 NAAQS

Under the CAA, we are to regulate HD emissions if they contribute
to air pollution that can reasonably be anticipated to endanger public
health and welfare. We have already addressed the question of what
concentration patterns of PM endanger public health, in setting the
NAAQS for PM10 in 1987. The PM NAAQS were revised in 1997,
largely by adding new standards for fine particles (PM2.5)
and modifying the form of the daily PM10 standard. On
judicial review, the revised standards were remanded for further
proceedings, and the revised PM10 standards were vacated.
EPA has sought Supreme Court review of that decision; pending final
resolution of the litigation, the 1987 PM10 standards
continue to apply.

i. Current PM10 Nonattainment

The most recent PM10 monitoring data indicates that 12
designated PM10 nonattainment areas, with a population of 19
million in 1990, violated the PM10 NAAQS in the period 1996-
1998. Table II.B-3 lists the 12 areas. The table also indicates the
classification and 1990 population for each area.

Table II.B-3.--PM10 Nonattainment Areas Violating the PM10 NAAQS in 1996-
1998 ^a
------------------------------------------------------------------------
1990 population
Area Classification (millions)
------------------------------------------------------------------------
Clark Co., NV................... Serious............ 0.741
El Paso, TX ^b................... Moderate........... 0.515
Hayden/Miami, AZ................ Moderate........... 0.003
Imperial Valley, CA ^b........... Moderate........... 0.092
Owens Valley, CA................ Serious............ 0.018
San Joaquin Valley, CA.......... Serious............ 2.564
Mono Basin, CA.................. Moderate........... 0.000
Phoenix, AZ..................... Serious............ 2.238
Fort Hall Reservation, ID....... Moderate........... 0.001
Los Angeles South Coast Air Serious............ 13.00
Basin, CA.
Nogales, AZ..................... Moderate........... 0.019
Wallula, WA ^c................... Moderate........... 0.048
------------------
Total population.......... 19.24
------------------------------------------------------------------------
\a\ In addition to these designated nonattainment areas, there are 15
unclassified counties, with a 1996 population of 4.2 million, for
which States have reported PM10 monitoring data for this period
indicating a PM10 NAAQS violation. Although we do not believe that we
are limited to considering only designated nonattainment areas as part
of this rulemaking, we have focused on the designated areas in the
case of PM10. An official designation of PM10 nonattainment indicates
the existence of a confirmed PM10 problem that is more than a result
of a one-time monitoring upset or a result of PM10 exceedances
attributable to natural events. We have not yet excluded the
possibility that one or the other of these is responsible for the
monitored violations in 1996-1998 in the 15 unclassified areas. We
adopted a policy in 1996 that allows areas whose PM10 exceedances are
attributable to natural events to remain unclassified if the State is
taking all reasonable measures to safeguard public health regardless
of the source of PM10 emissions. Areas that remain unclassified areas
are not required to submit attainment plans, but we work with each of
these areas to understand the nature of the PM10 problem and to
determine what best can be done to reduce it.
\b\ EPA has determined that PM10 nonattainment in these areas is
attributable to international transport. While reductions in heavy-
duty vehicle emissions cannot be expected to result in attainment,
they will reduce the degree of PM10 nonattainment to some degree.
\c\ The violation in this area has been determined to be attributable to
natural events.

ii. Risk of Future Exceedances of the PM10 Standard

The proposed new standards for heavy-duty vehicles will benefit
public health and welfare through reductions in direct diesel particles
and NO_X, VOCs, and SO_X which contribute to
secondary formation of particulate matter. Because ambient particle
concentrations causing violations of the PM10 standard are
well established to endanger public health and welfare, this
information supports the proposed new standards for heavy-duty
vehicles. The Agency's recent PM modeling analysis

[[Page 35448]]

performed for the Tier 2 rulemaking predicts that a significant number
of areas across the nation are at risk of failing to meet the
PM10 NAAQS even with Tier 2 and other controls currently in
place. These reductions will assist states as they work with the Agency
through SIP development and implementation of local controls to move
their areas into attainment by the applicable deadline, and maintain
the standards thereafter.
The Agency believes that the PM10 concentrations in 10
areas shown in Table II.B-4 have a significant risk of exceeding the
PM10 standard without further emission reductions during the
time period when this rulemaking would take effect. This belief is
based on the PM10 modeling conducted for the Tier 2
rulemaking. Table II.B-4 presents information about these 10 areas and
subdivides them into two groups. The first group of six areas are
designated PM10 nonattainment areas which had recent
monitored violations of the PM10 NAAQS in 1996-1998 and were
predicted to be in nonattainment in 2030 in our PM10 air
quality modeling. These areas have a population of over 19 million.
Included in the group are the nonattainment areas that are part of the
Los Angeles, Phoenix, and Las Vegas metropolitan areas, where traffic
from heavy-duty vehicles is substantial. These six areas would clearly
benefit from the reductions in emissions that would occur from the
proposed new standards for heavy-duty vehicles.
The second group of four counties listed in Table II.B-4 with a
total of 8 million people in 1996 also had predicted exceedances of the
PM10 standard. However, while these four areas registered,
in either 1997 or 1998, single-year annual average monitored
PM10 levels of at least 90 percent of the PM10
NAAQS, these areas did not exceed the formal definition of the
PM10 NAAQS over the three-year period ending in 1998.\30\
Unlike the situation for ozone, for which precursor emissions are
generally declining over the next 10 years or so before beginning to
increase, we estimate that emissions of PM10 will rise
steadily unless new controls are implemented. The small margin of
attainment which the four areas currently enjoy will likely erode; the
PM air quality modeling suggests that it will be reversed. We therefore
consider these four areas to each individually have a significant risk
of exceeding the PM10 standard without further emission
reductions. The emission reductions from the proposed new standards for
heavy-duty vehicles would help these areas with attainment and maintain
in conjunction with other processes that are currently moving these
areas towards attainment.
---------------------------------------------------------------------------

\30\ In fact, in two of these areas, New York Co., NY and Harris
Co., TX, the average PM10 level in 1998 was above the 50
micrograms per cubic meter value of the NAAQS. These two areas are
not characterized in Table II.B-4 as areas with a high risk of
failing to attain and maintain because lower PM10 levels
in 1996 and 1997 caused their three-year average PM10
level to be lower than the NAAQS. Official nonattainment
determinations for the annual PM10 NAAQS are made based
on the average of 12 quarterly PM10 averages.

Table II.B-4.--Areas With Significant Risk of Exceeding the PM10 NAAQS
Without Further Emission Reductions
------------------------------------------------------------------------
1990 population
Area (millions)
------------------------------------------------------------------------
Areas Currently Exceeding the PM10 Standard:
Clark Co., NV.............................. 0.741
El Paso, TX ^a.............................. 0.515
Imperial Valley, CA ^a...................... 0.092
San Joaquin Valley, CA..................... 2.564
Phoenix, AZ................................ 2.238
Los Angeles South Coast Air Basin, CA...... 13.00
------------------------
Subtotal for 6 Areas..................... 19.15
========================
Areas within 10% of Exceeding the PM10
Standard:
New York Co., NY........................... 1.49
Cuyahoga Co., OH........................... 1.41
Harris, Co., TX............................ 2.83
San Diego Co., CA.......................... 2.51
------------------------
Subtotal for 4 Areas..................... 8.24
========================
Total 1996 Population of All 10 Areas at 27.39
Risk of Exceeding the PM10 Standard: 10
Areas, Total 1990 Population............
------------------------------------------------------------------------
\a\ EPA has determined that PM10 nonattainment in these areas is
attributable to international transport. While reductions in heavy-
duty vehicle emissions cannot be expected to result in attainment,
they will reduce the degree of PM10 nonattainment to some degree.

Future concentrations of ambient particulate matter may be
influenced by the potentially significant influx of diesel-powered cars
and light trucks into the light duty vehicle fleet. At the present
time, virtually all cars and light trucks being sold are gasoline
fueled. However, the possibility exists that diesels will become more
prevalent in the car and light-duty truck fleet, since automotive
companies have announced their desire to increase their sales of diesel
cars and light trucks. For the Tier 2 rulemaking, the Agency performed
a sensitivity analysis using A.D.Little's ``most likely'' increased
growth scenario of diesel penetration into the light duty vehicle fleet
which culminated in a 9 percent and 24 percent penetration of diesel
vehicles in the LDV and LDT markets, respectively, in 2015 (see Tier 2
RIA, Table III.A.-13). This scenario is relevant for the purpose of
this rulemaking because, according to the analysis performed in Tier 2,
an increased number of diesel-powered light duty vehicles will increase
LDV PM emissions by about 13 percent in 2010 rising to 19 percent in
2030, even with the stringent new PM standards established under the
Tier 2 rule. If manufacturers elect to certify a portion of their
diesel-powered LDVs to the least-stringent PM standard available under
the Tier 2 bin structure, the increase in LDV PM emissions could be

[[Page 35449]]

even greater, thus potentially exacerbating PM10
nonattainment problems.
EPA recognizes that the SIP process is ongoing and that many of the
six current nonattainment areas in Table II.B-4 are in the process of,
or will be adopting additional control measures to achieve the
PM10 NAAQS in accordance with their attainment dates under
the Clean Air Act. EPA believes, however, that as in the case of ozone,
there are uncertainties inherent in any demonstration of attainment
that is premised on forecasts of emission levels and meteorology in
future years. Therefore, even if these areas adopt and submit SIPs that
EPA is able to approve as demonstrating attainment of the
PM10 standard, the modeling conducted for Tier 2 and the
history of PM10 levels in these areas indicates that there
is still a significant risk that these areas would need the reductions
from the proposed heavy-duty vehicle standards to maintain the
PM10 standards in the long term. The other four areas in
Table II.B-4 also have a significant risk of experiencing violations of
the PM10 standard.
In sum, the Agency believes that all 10 areas have a significant
risk of experiencing particulate matter levels that violate the
PM10 standard during the time period when this proposed rule
would take effect. These 10 areas have a combined population of 27
million, and are located throughout the nation. In addition, this list
does not fully consider the possibility that there are other areas
which are now meeting the PM10 NAAQS that have at least a
significant probability of requiring further reductions to continue to
maintain it.

e. Public Health and Welfare Concerns From Exposure to Fine PM

Many epidemiologic studies have shown statistically significant
associations of ambient PM levels with a variety of human health
endpoints in sensitive populations, including mortality, hospital
admissions and emergency room visits, respiratory illness and symptoms
measured in community surveys, and physiologic changes in mechanical
pulmonary function. These effects have been observed in many areas with
ambient PM levels at or below the current PM10 NAAQS. The
epidemiologic science points to fine PM as being more strongly
associated with some health effects, such as premature mortality, than
coarse fraction PM.
Associations of both short-term and long-term PM exposure with most
of the above health endpoints have been consistently observed. (A more
detailed discussion may be found in the RIA.) The general internal
consistency of the epidemiologic data base and available findings have
led to increasing public health concern, due to the severity of several
studied endpoints and the frequent demonstration of associations of
health and physiologic effects with ambient PM levels at or below the
current PM10 NAAQS. The weight of epidemiologic evidence
suggests that ambient PM exposure has affected the public health of
U.S. populations. Specifically, increased mortality associated with
fine PM was observed in cities with longer-term average fine PM
concentrations in the range of 16 to 21 ug/m3. For example, over 113
million people (46 percent of continental US population, 1990) lived in
areas in 1996 where long term ambient fine particulate matter levels
were at or above 16 g/m³, which is the long term
average PM2.5 concentration that prevailed in Boston during
the study which found that acute mortality was statistically
significantly associated with daily fine PM concentrations.\31\ It is
reasonable to anticipate that sensitive populations exposed to similar
or higher levels, now and in the 2007 and later time frame, will also
be at increased risk of premature mortality associated with exposures
to fine PM. In addition, statistically significant relationships have
also been observed in U.S. cities between PM levels and increased
respiratory symptoms and decreased lung functions in children.
---------------------------------------------------------------------------

\31\ In the absence of quality-assured PM2.5
monitoring data, we have used an air quality model called Regional
Modeling System for Aerosols and Deposition (REMSAD) to estimate
recent PM2.5 concentrations across the U.S. for 1996.
Essentially, REMSAD is a three-dimensional grid-based Eulerian air
quality model designed to simulate long-term (e.g., annual)
concentrations and deposition of atmospheric pollutants (e.g.,
particulates and toxics) over large spatial scales (e.g., over the
contiguous United States). A more detailed explanation of the
methodology is found in the draft RIA.
---------------------------------------------------------------------------

While uncertainty remains in the published data base regarding
specific aspects about the nature and magnitude of the overall public
health risk imposed by ambient PM exposure, we believe that the body of
health evidence is supportive of our view that PM exposures that can
reasonably be anticipated to occur in the future are a serious public
health concern warranting a requirement to reduce emissions from heavy-
duty vehicles, even at levels below the PM10 NAAQS. EPA
believes the risk is significant from an overall public health
perspective because of the large number of individuals in sensitive
populations that we expect to be exposed to ambient fine PM in the 2007
and later time frame, as well as the importance of the negative health
affects.
We believe the evidence regarding the occurrence of adverse health
effects due to exposure to fine PM concentrations, and regarding the
populations that are expected to receive exposures at these levels,
supports a proposed conclusion that emissions from heavy-duty vehicles
that lead to the formation of fine PM in 2007 and later will be
contributing to a national air pollution problem that warrants action
under section 202(a)(3).

f. Visibility and Regional Haze Effects of Ambient PM

Visibility impairment, also called regional haze, is a complex
problem caused by a variety of sources, both natural and anthropogenic
(e.g., motor vehicles). Regional haze masks objects on the horizon and
reduces the contrast of nearby objects. The formation, extent, and
intensity of regional haze are functions of meteorological and chemical
processes, which sometimes cause fine particle loadings to remain
suspended in the atmosphere for several days and to be transported
hundreds of kilometers from their sources (NRC, 1993).
Visibility has been defined as the degree to which the atmosphere
is transparent to visible light (NRC, 1993). Visibility impairment is
caused by the scattering and absorption of light by particles and gases
in the atmosphere. Fine particles (0.1 to 1.0 microns in diameter) are
more effective per unit mass concentration at impairing visibility than
either larger or smaller particles (NAPAP, 1991). Most of the diesel
particle mass emitted by diesel engines falls within this fine particle
size range. Light absorption is often caused by elemental carbon, a
product of incomplete combustion from activities such as burning diesel
fuel or wood. These particles cause light to be scattered or absorbed,
thereby reducing visibility.
Heavy-duty vehicles contribute a significant portion of the
emissions of direct PM, NO_X, and SO_X that result
in ambient PM that contributes to regional haze and impaired
visibility. The Grand Canyon Visibility Transport Commission's report
found that reducing total mobile source emissions is an essential part
of any program to protect visibility in the Western U.S. The Commission
identified mobile source pollutants of concern as VOC, NO_X,
and elemental and organic carbon. The Western Governors Association, in
later commenting on the Regional Haze Rule and on protecting the 16
Class I

[[Page 35450]]

areas on the Colorado Plateau, stated that the federal government, and
particularly EPA, must do its part in regulating emissions from mobile
sources that contribute to regional haze in these areas. As described
more fully later in this section, today's proposal would result in
large reductions in these pollutants. These reductions are expected to
provide an important step towards improving visibility across the
nation. Emissions reductions being achieved to attain the 1-hour ozone
and PM10 NAAQS will assist in visibility improvements, but
not substantially. Moreover, the timing of the reductions from the
proposed standards fits very well with the goals of the regional haze
program. We will work with the regional planning bodies to make sure
they have the information to take account of the reductions from any
final rule resulting from this proposal in their planning efforts.
The Clean Air Act contains provisions designed to protect national
parks and wilderness areas from visibility impairment. In 1999, EPA
promulgated a rule that will require States to develop plans to
dramatically improve visibility in national parks. Although it is
difficult to determine natural visibility levels, we believe that
average visual range in many Class I areas in the United States is
significantly less (about 50-66% of natural visual range in the West,
about 20% of natural visual range in the East) than the visual range
that would exist without anthropogenic air pollution. The final
Regional Haze Rule establishes a 60-year time period for planning
purposes, with several near term regulatory requirements, and is
applicable to all 50 states. One of the obligations is for States to
conduct visibility monitoring in mandatory Class I Federal areas and
determine baseline conditions using data for year 2000 to 2004.
Reductions of particles, NO_X, sulfur, and VOCs from this
rulemaking would have a significant impact on moving all states towards
achieving long-term visibility goals, as outlined in the 1999 Regional
Haze Rule.

g. Other Welfare Effects Associated With PM

The deposition of airborne particles reduces the aesthetic appeal
of buildings, and promotes and accelerates the corrosion of metals,
degrades paints, and deteriorates building materials such as concrete
and limestone. This materials damage and soiling are related to the
ambient levels of airborne particulates, which are emitted by heavy-
duty vehicles. Although there was insufficient data to relate materials
damage and soiling to specific concentrations, and thereby to allow the
Agency to establish a secondary PM standard for these impacts, we
believe that the welfare effects are real and that heavy-duty vehicle
PM, NO_X, SO_X, and VOC contribute to materials
damage and soiling.

h. Conclusions Regarding PM

There is a significant risk that, despite statutory requirements
and EPA and state efforts towards attainment and maintenance, some
areas of the U.S. will violate the PM10 NAAQS in 2007 and
thereafter. We believe that the information provided in this section
shows that there will be air pollution that warrants regulatory
attention under section 202(a)(3) of the Act. Heavy-duty vehicles
contribute substantially to PM10 levels, as shown in section
II.C below.
It is also reasonable to anticipate that concentrations of fine PM,
as represented for example by PM2.5 concentrations, will
endanger public health and welfare also even if all areas attain and
maintain the PM10 NAAQS. Heavy-duty vehicles will also
contribute to this air pollution problem.
There are also important environmental impacts of PM10,
such as regional haze which impairs visibility. Furthermore, while the
evidence on soiling and materials damage is limited and the magnitude
of the impact of heavy-duty vehicles on these welfare effects is
difficult to quantify, these welfare effects support our belief
information that this proposal is necessary and appropriate.
3. Other Criteria Pollutants
The standards being proposed today would help reduce levels of
three other pollutants for which NAAQS have been established: carbon
monoxide (CO), nitrogen dioxide (NO2), and sulfur dioxide
(SO2). The extent of nonattainment for these three
pollutants is small, so the primary effect of today's proposal would be
to provide areas concerned with maintaining their attainment status a
greater margin of safety. As of 1998, every area in the United States
has been designated to be in attainment with the NO2 NAAQS.
As of 1997, only one area (Buchanan County, Missouri) did not meet the
primary SO2 short-term standard, due to emissions from the
local power plant. In 1997, only 6 of 537 monitoring sites reported
ambient CO levels in excess of the CO NAAQS. There are currently 20
designated CO nonattainment areas, with a combined population of 34
million. There are also 23 designated maintenance areas with an
additional combined population of 34 million. The broad trends indicate
that ambient levels of CO are declining.
4. Other Air Toxics
In addition to NO_X and particulates, heavy-duty vehicle
emissions contain several other substances that are known or suspected
human or animal carcinogens, or have serious noncancer health effects.
These include benzene,1,3-butadiene, formaldehyde, acetaldehyde,
acrolein, and dioxin. For some of these pollutants, heavy-duty engine
emissions are believed to account for a significant proportion of total
nation-wide emissions. Although these emissions will decrease in the
short term, they are expected to increase in 2007-2020 without the
proposed emission limits, as the number of miles traveled by heavy-duty
trucks increases. In the Draft RIA, we present current and projected
exposures to benzene, 1,3-butadiene, formaldehyde, and acetaldehyde
from all on-highway motor vehicles.
By reducing hydrocarbon and other organic emissions, both in gas
phase and bound to particles, the emission control program proposed in
today's action would have a significant impact on direct emissions of
air toxics from HDVs. We are also proposing a new formaldehyde standard
for heavy-duty vehicles. Today's action would reduce exposure to these
substances and therefore help reduce the impact of HDV emissions on
cancer and non-cancer health effects. We are currently conducting a
risk assessment to assess the risk of cancer in the population that can
be attributed to motor vehicle emissions of benzene, 1,3-butadiene,
formaldehyde, and acetaldehyde.

a. Benzene

Highway mobile sources account for 52 percent of nationwide
emissions of benzene and HDVs account for 7 percent of all highway
vehicle benzene emissions.\32\ The EPA has recently reconfirmed that
benzene is a known human carcinogen by all routes of exposure
(including leukemia at high, prolonged air exposures), and is
associated with additional health effects including genetic changes in
humans and animals and increased proliferation

[[Page 35451]]

of bone marrow cells in mice.\33\ \34\ \35\ EPA believes that the data
indicate a causal relationship between benzene exposure and acute
lymphocytic leukemia and suggest a relationship between benzene
exposure and chronic non-lymphocytic leukemia and chronic lymphocytic
leukemia. Respiration is the major source of human exposure and at
least half of this exposure is attributable to gasoline vapors and
automotive emissions. A number of adverse noncancer health effects
including blood disorders, such as preleukemia and aplastic anemia,
have also been associated with low-dose, long-term exposure to benzene.
---------------------------------------------------------------------------

\32\ 1990 Emissions Inventory of Forty Potential Section 112(k)
Pollutants: Supporting Data for EPA's Section 112(k) Regulatory
Strategy--Final Report. Emission Factors and Inventory Group, Office
of Air Quality Planning and Standards, May, 1999.
\33\ International Agency for Research on Cancer, IARC
monographs on the evaluation of carcinogenic risk of chemicals to
humans, Volume 29, Some industrial chemicals and dyestuffs,
International Agency for Research on Cancer, World Health
Organization, Lyon, France, p. 345-389, 1982.
\34\ Irons, R.D., W.S. Stillman, D.B. Calogiovanni, and V.A.
Henry, Synergistic action of the benzene metabolite hydroquinone on
myelopoietic stimulating activity of granulocyte/macrophage colony-
stimulating factor in vitro, Proc. Natl. Acad. Sci. 89:3691-3695,
1992.
\35\ Environmental Protection Agency, Carcinogenic Effects of
Benzene: An Update, National Center for Environmental Assessment,
Washington, DC. 1998.
---------------------------------------------------------------------------

b. 1,3-Butadiene

Highway mobile sources account for 51 percent of the annual
emissions of 1,3-butadiene and HDVs account for 15 percent of the
highway vehicle portion. Today's program would play an important role
in reducing in the mobile contribution of 1,3-butadiene. This compound
causes a variety of reproductive and developmental effects in mice and
rats exposed to long-term, low doses. There is, however, no human data
on 1,3-butadiene. EPA's recently prepared draft health assessment
document presents evidence that suggests this substance is a known
human carcinogen.\36\ The Environmental Health Committee of EPA's
Science Advisory Board, in reviewing EPA's draft Health Assessment for
1,3-butadiene, recommended that 1,3-butadiene should be classified as a
probable human carcinogen.\37\
---------------------------------------------------------------------------

\36\ Environmental Protection Agency, Health Risk Assessment of
1,3-Butadiene. EPA/600/P-98/001A, February 1998.
\37\ An SAB Report: Review of the Health Risk Assessment of 1,3-
Butadiene. EPA-SAB-EHC-98, August, 1998.
---------------------------------------------------------------------------

c. Formaldehyde

Highway mobile sources contribute 27 percent of the national
emissions of formaldehyde, and HDVs account for 35 percent of the
highway portion. EPA has classified formaldehyde as a probable human
carcinogen based on evidence in humans and in rats, mice, hamsters, and
monkeys.\38\ Epidemiological studies in occupationally exposed workers
suggest that long-term inhalation of formaldehyde may be associated
with tumors of the nasopharyngeal cavity (generally the area at the
back of the mouth near the nose), nasal cavity, and sinus. Formaldehyde
exposure also causes a range of noncancer health effects, including
irritation of the eyes (tearing of the eyes and increased blinking) and
mucous membranes. Sensitive individuals may experience these adverse
effects at lower concentrations than the general population and in
persons with bronchial asthma, the upper respiratory irritation caused
by formaldehyde can precipitate an acute asthmatic attack.
---------------------------------------------------------------------------

\38\ Environmental Protection Agency, Assessment of health risks
to garment workers and certain home residents from exposure to
formaldehyde, Office of Pesticides and Toxic Substances, April 1987.
---------------------------------------------------------------------------

d. Acetaldehyde

Highway mobile sources contribute 20 percent of the national
acetaldehyde emissions and HDVs are responsible for approximately 33
percent of these highway mobile source emissions. Acetaldehyde is
classified as a probable human carcinogen and is considered moderately
toxic by the inhalation, oral, and intravenous routes. The primary
acute effect of exposure to acetaldehyde vapors is irritation of the
eyes, skin, and respiratory tract. At high concentrations, irritation
and pulmonary effects can occur, which could facilitate the uptake of
other contaminants.

e. Acrolein

HDVs are responsible for approximately 53 percent of the mobile
source highway emissions and about 8% of the total inventory (1996
NTI). Acrolein is extremely toxic to humans when inhaled, with acute
exposure resulting in upper respiratory tract irritation and
congestion. The Agency has developed a reference concentration for
inhalation (RfC) of acrolein of 0.02 micrograms/m³.\39\
Although no information is available on its carcinogenic effects in
humans, based on laboratory animal data, EPA considers acrolein a
possible human carcinogen.
---------------------------------------------------------------------------

\39\ U.S. EPA (1993) Environmental Protection Agency, Integrated
Risk Information System (IRIS), Office of Health and Environmental
Assessment, Environmental Criteria and Assessment Office,
Cincinnati, OH.
---------------------------------------------------------------------------

f. Dioxins

Recent studies have confirmed that dioxins are formed by and
emitted from heavy-duty diesel trucks. These trucks are estimated to
account for 1.2 percent of total dioxin emissions. In general, dioxin
exposures of concern have primarily been noninhalation exposures
associated with human ingestion of certain foods (e.g., beef,
vegetables, and dairy products contaminated by dioxin). EPA has
classified dioxin as a probable human carcinogen. Acute and chronic
effects have also been reported for dioxin from oral and inhalation
routes of exposure.\40\
---------------------------------------------------------------------------

\40\ U.S. EPA (1994) Health Assessment Document for 2,3,7,8-
Tetrachlorodibenzo-p-dioxin (TCDD) and Related Compounds: Volume III
Summary Draft Document. EPA/600/BP-92/001c.
---------------------------------------------------------------------------

5. Other Environmental Effects

a. Acid Deposition

Acid deposition, or acid rain as it is commonly known, occurs when
SO2 and NO_X react in the atmosphere with water,
oxygen, and oxidants to form various acidic compounds that later fall
to earth in the form of precipitation or dry deposition of acidic
particles.\41\ It contributes to damage of trees at high elevations and
in extreme cases may cause lakes and streams to become so acidic that
they cannot support aquatic life. In addition, acid deposition
accelerates the decay of building materials and paints, including
irreplaceable buildings, statues, and sculptures that are part of our
nation's cultural heritage. To reduce damage to automotive paint caused
by acid rain and acidic dry deposition, some manufacturers use acid-
resistant paints, at an average cost of $5 per vehicle--a total of $61
million per year if applied to all new cars and trucks sold in the U.S.
---------------------------------------------------------------------------

\41\ Much of the information in this subsection was excerpted
from the EPA document, Human Health Benefits from Sulfate Reduction,
written under Title IV of the 1990 Clean Air Act Amendments, U.S.
EPA, Office of Air and Radiation, Acid Rain Division, Washington, DC
20460, November 1995.
---------------------------------------------------------------------------

Acid deposition primarily affects bodies of water that rest atop
soil with a limited ability to neutralize acidic compounds. The
National Surface Water Survey (NSWS) investigated the effects of acidic
deposition in over 1,000 lakes larger than 10 acres and in thousands of
miles of streams. It found that acid deposition was the primary cause
of acidity in 75 percent of the acidic lakes and about 50 percent of
the acidic streams, and that the areas most sensitive to acid rain were
the Adirondacks, the mid-Appalachian highlands, the upper Midwest and
the high elevation West. The NSWS found that approximately 580 streams
in the Mid-Atlantic Coastal Plain are acidic primarily due to acidic
deposition. Hundreds of the lakes in the Adirondacks surveyed in the
NSWS

[[Page 35452]]

have acidity levels incompatible with the survival of sensitive fish
species. Many of the over 1,350 acidic streams in the Mid-Atlantic
Highlands (mid-Appalachia) region have already experienced trout losses
due to increased stream acidity. Emissions from U.S. sources contribute
to acidic deposition in eastern Canada, where the Canadian government
has estimated that 14,000 lakes are acidic. Acid deposition also has
been implicated in contributing to degradation of high-elevation spruce
forests that populate the ridges of the Appalachian Mountains from
Maine to Georgia. This area includes national parks such as the
Shenandoah and Great Smoky Mountain National Parks.
The SO_X and NO_X reductions from today's
proposal would help reduce acid rain and acid deposition, thereby
helping to reduce acidity levels in lakes and streams throughout the
country and help accelerate the recovery of acidified lakes and streams
and the revival of ecosystems adversely affected by acid deposition.
Reduced acid deposition levels would also help reduce stress on
forests, thereby accelerating reforestation efforts and improving
timber production. Deterioration of our historic buildings and
monuments, and of buildings, vehicles, and other structures exposed to
acid rain and dry acid deposition also would be reduced, and the costs
borne to prevent acid-related damage may also decline. While the
reduction in sulfur and nitrogen acid deposition would be roughly
proportional to the reduction in SO_X and NO_X
emissions, respectively, the precise impact of today's proposal would
differ across different areas.

b. Eutrophication and Nitrification

Nitrogen deposition into bodies of water can cause problems beyond
those associated with acid rain. The Ecological Society of America has
included discussion of the contribution of air emissions to increasing
nitrogen levels in surface waters in a recent major review of causes
and consequences of human alteration of the global nitrogen cycle in
its Issues in Ecology series.\42\ Long-term monitoring in the United
States, Europe, and other developed regions of the world shows a
substantial rise of nitrogen levels in surface waters, which are highly
correlated with human-generated inputs of nitrogen to their watersheds.
These nitrogen inputs are dominated by fertilizers and atmospheric
deposition.
---------------------------------------------------------------------------

\42\ Vitousek, Peter M., John Aber, Robert W. Howarth, Gene E.
Likens, et al. 1997. Human Alteration of the Global Nitrogen Cycle:
Causes and Consequences. Issues in Ecology. Published by Ecological
Society of America, Number 1, Spring 1997.
---------------------------------------------------------------------------

Human activity can increase the flow of nutrients into those waters
and result in excess algae and plant growth. This increased growth can
cause numerous adverse ecological effects and economic impacts,
including nuisance algal blooms, dieback of underwater plants due to
reduced light penetration, and toxic plankton blooms. Algal and
plankton blooms can also reduce the level of dissolved oxygen, which
can also adversely affect fish and shellfish populations. This problem
is of particular concern in coastal areas with poor or stratified
circulation patterns, such as the Chesapeake Bay, Long Island Sound, or
the Gulf of Mexico. In such areas, the ``overproduced'' algae tends to
sink to the bottom and decay, using all or most of the available oxygen
and thereby reducing or eliminating populations of bottom-feeder fish
and shellfish, distorting the normal population balance between
different aquatic organisms, and in extreme cases causing dramatic fish
kills.
Collectively, these effects are referred to as eutrophication,
which the National Research Council recently identified as the most
serious pollution problem facing the estuarine waters of the United
States (NRC, 1993). Nitrogen is the primary cause of eutrophication in
most coastal waters and estuaries.\43\ On the New England coast, for
example, the number of red and brown tides and shellfish problems from
nuisance and toxic plankton blooms have increased over the past two
decades, a development thought to be linked to increased nitrogen
loadings in coastal waters. Airborne NO_X contributes from 12
to 44 percent of the total nitrogen loadings to United States coastal
water bodies. For example, approximately one-quarter of the nitrogen in
the Chesapeake Bay comes from atmospheric deposition.
---------------------------------------------------------------------------

\43\ Much of this information was taken from the following EPA
document: Deposition of Air Pollutants to the Great Waters-Second
Report to Congress, Office of Air Quality Planning and Standards,
June 1997, EPA-453/R-97-011. A Third Report to Congress on
Deposition of Air Pollutants to the Great Waters will be forthcoming
the the next month. We will update this section with information
from the Third Report in the final rule.
---------------------------------------------------------------------------

Excessive fertilization with nitrogen-containing compounds can also
affect terrestrial ecosystems.\44\ Research suggests that nitrogen
fertilization can alter growth patterns and change the balance of
species in an ecosystem. In extreme cases, this process can result in
nitrogen saturation when additions of nitrogen to soil over time exceed
the capacity of the plants and microorganisms to utilize and retain the
nitrogen. This phenomenon has already occurred in some areas of the
U.S.
---------------------------------------------------------------------------

\44\ Terrestrial nitrogen deposition can act as a fertilizer. In
some agricultural areas, this effect can be beneficial.
---------------------------------------------------------------------------

Deposition of nitrogen from heavy-duty vehicles contributes to
these problems. In the Chesapeake Bay region, modeling shows that
mobile source deposition occurs in relatively close proximity to
highways, such as the I-95 corridor which covers part of the Bay
surface. The proposed new standards for heavy-duty vehicles would
reduce total NO_X emissions by 2.8 million tons in 2030. The
NO_X reductions should reduce the eutrophication problems
associated with atmospheric deposition of nitrogen into watersheds and
onto bodies of water, particularly in aquatic systems where atmospheric
deposition of nitrogen represents a significant portion of total
nitrogen loadings.

c. POM Deposition

EPA's Great Waters Program has identified 15 pollutants whose
deposition to water bodies has contributed to the overall contamination
loadings to the these Great Waters.\45\ One of these 15 pollutants, a
group known as polycyclic organic matter (POM), are compounds that are
mainly adhered to the particles emitted by mobile sources and later
fall to earth in the form of precipitation or dry deposition of
particles. The mobile source contribution of the 7 most toxic POM is at
least 62 tons/year and represents only those POM that adhere to mobile
source particulate emissions.\46\ The majority of these emissions are
produced by diesel engines.
---------------------------------------------------------------------------

\45\ Much of this information was taken from the following EPA
document: Deposition of Air Pollutants to the Great Waters-Second
Report to Congress, Office of Air Quality Planning and Standards,
June 1997, EPA-453/R-97-011. You are referred to that document for a
more detailed discussion. A Third Report to Congress on Deposition
of Air Pollutants to the Great Waters will be forthcoming the the
next month. We will update this section with information from the
Third Report in the final rule.
\46\ The 1996 National Toxics Inventory, Office of Air Quality
Planning and Standards, October 1999.
---------------------------------------------------------------------------

POM is generally defined as a large class of chemicals consisting
of organic compounds having multiple benzene rings and a boiling point
greater than 100 deg.C. Polycyclic aromatic hydrocarbons are a chemical
class that is a subset of POM. POM are naturally occurring substances
that are byproducts of the incomplete combustion of fossil fuels and
plant and animal biomass (e.g., forest fires). Also, they occur as
byproducts from steel and

[[Page 35453]]

coke productions and waste incineration.
Evidence for potential human health effects associated with POM
comes from studies in animals (fish, amphibians, rats) and in human
cells culture assays. Reproductive, developmental, immunological, and
endocrine (hormone) effects have been documented in these systems. Many
of the compounds included in the class of compounds known as POM are
classified by EPA as probable human carcinogens based on animal data.
The particulate reductions from today's proposal would help reduce
not only the particulate emissions from highway diesel engines but also
the deposition of the POM adhering to the particles, thereby helping to
reduce health effects of POM in lakes and streams, accelerate the
recovery of affected lakes and streams, and revive the ecosystems
adversely affected.

C. Contribution from Heavy-Duty Vehicles

Nationwide, heavy-duty vehicles contribute about 15 percent of the
total NO_X inventory, and 29 percent of the mobile source
inventory. Heavy-duty NO_X emissions also contribute to fine
particulate concentrations in ambient air due to the transformation in
the atmosphere to nitrates. The NO_X reductions resulting
from today's proposed standards would therefore have a considerable
impact on the national NO_X inventory. Light and heavy-duty
mobile sources account for 24 percent of the PM10 (excluding
the contribution of miscellaneous and natural sources), and heavy-duty
vehicles account for 14 percent of the mobile source portion of
national PM10 emissions. The heavy-duty portion of the
inventory is often greater in the cities, and the reductions proposed
in this rulemaking would have a relatively greater benefit in those
areas.
1. NO_X Emissions
Heavy-duty vehicles are important contributors to the national
inventories of NO_X emissions, and they contribute moderately
to national VOC pollution. The Draft RIA for this proposal describes in
detail recent emission inventory modeling completed by EPA. HDVs are
expected to contribute approximately 15 percent of annual
NO_X emissions in 2007 (Table II.C-1).

Table II.C-1.--2007 Heavy-Duty Vehicle Contribution to Urban NO_X
Inventories
[Amounts in percent]
------------------------------------------------------------------------
Portion
Portion of
Metropolitan statistical area of mobile
total source
NO_X NO_X
------------------------------------------------------------------------
National.............................................. 15% 29%
Albuquerque........................................... 25% 38%
Atlanta............................................... 23% 36%
San Francisco......................................... 23% 29%
Spokane............................................... 23% 29%
Seattle............................................... 22% 26%
Dallas................................................ 22% 28%
Charlotte............................................. 21% 34%
Washington............................................ 20% 37%
Los Angeles........................................... 20% 26%
San Antonio........................................... 20% 31%
New York.............................................. 19% 30%
Miami................................................. 18% 23%
Phoenix............................................... 18% 28%
Philadelphia.......................................... 18% 30%
Cleveland............................................. 17% 30%
St. Louis............................................. 16% 34%
------------------------------------------------------------------------

The contribution of heavy-duty vehicles to NO_X
inventories in many MSAs is significantly greater than that reflected
in the national average. For example, HDV contributions to
NO_X in Albuquerque, Atlanta, San Francisco, Spokane,
Seattle, and Dallas are projected to be 22 to 25 percent of the MSA-
specific inventories in 2007, which is significantly higher than the
national average. These data are based largely on our Tier 2
inventories and have been adjusted to reflect new information regarding
the VMT split between light-duty and heavy-duty vehicles as discussed
in the draft RIA. These data will be further updated for the final rule
to reflect more recent modeling.
2. PM Emissions
Nationally, we estimate that primary emissions of PM10
to be about 33.2 million tons/year in 2007. Fugitive dust, other
miscellaneous sources and crustal material (wind erosion) comprise
approximately 90 percent of the 2007 PM10 inventory.
However, there is evidence from ambient studies that emissions of these
materials may be overestimated and/or that once emitted they have less
of an influence on monitored PM concentration than this inventory share
would suggest. Mobile sources account for 24 percent of the
PM10 inventory (excluding the contribution of miscellaneous
and natural sources) and highway heavy-duty engines, the subject of
today's action, account for 14 percent of the mobile source portion of
national PM10 emissions.
The contribution of heavy-duty vehicle emissions to total PM
emissions in some metropolitan areas is substantially higher than the
national average. This is not surprising, given the high density of
these engines operating in these areas. For example, in Albuquerque,
Pittsburgh, St. Louis, and Atlanta, the estimated 2007 highway heavy-
duty vehicle contribution to mobile source PM10 ranges from
16 to 21 percent, and the national percent contribution to mobile
sources for 2007 is projected to be about 14 percent. As illustrated in
Table II.C-2 , heavy-duty vehicles operated Washington, Fairbanks,
Billings, and Detroit also account for a slightly higher portion of the
mobile source PM inventory than the national average. These data are
based largely on our Tier 2 inventories and have been adjusted to
reflect new information regarding the VMT split between light-duty and
heavy-duty vehicles as discussed in the draft RIA. These data will be
further updated for the final rule to reflect more recent modeling.
Importantly, these estimates do not include the contribution from
secondary PM which is an important component of diesel PM.

Table II.C-2.--2007 Heavy-Duty Vehicle Contribution to Urban Mobile
Source PM Inventories
------------------------------------------------------------------------
PM10
contribution
Metropolitan statistical area from HDVs
(in percent)
------------------------------------------------------------------------
National.................................................. 14
Albuquerque............................................... 21
Pittsburgh................................................ 18
St. Louis................................................. 17
Atlanta................................................... 16
Washington................................................ 15
Fairbanks................................................. 15
Billings.................................................. 15
Detroit................................................... 15
------------------------------------------------------------------------

In addition to the national inventories, investigations have been
conducted in certain urban areas which provide information about the
contribution of HD diesel vehicles and engines to ambient
PM2.5 concentrations. This is particularly relevant as
diesel PM, for the most part, is composed of fine particles under 2.5
microns. Information about ambient concentrations of diesel PM and the
relative contribution of diesel engines to ambient PM levels is
available from source-receptor models, dispersion models, and elemental
carbon measurements. The most commonly used receptor model for
quantifying concentrations of diesel PM at a

[[Page 35454]]

receptor site is the chemical mass balance model (CMB). Input to the
CMB model includes PM measurements made at the receptor site as well as
measurements made of each of the source types suspected to impact the
site. Because of problems involving the elemental similarity between
diesel and gasoline emission profiles and their co-emission in time and
space, it is necessary to carefully quantify chemical molecular species
that provide markers for separation of these sources. Recent advances
in chemical analytical techniques have facilitated the development of
sophisticated molecular source profiles, including detailed speciation
of organic compounds, which allow the apportionment of PM to gasoline
and diesel sources with increased certainty. Older studies that made
use of only elemental source profiles have been published and are
summarized here, but are subject to more uncertainty. It should be
noted that since receptor modeling is based on the application of
source profiles to ambient measurements, this estimate of diesel PM
concentrations does not distinguish between on-road and non-road
sources for diesel PM. In addition, this model accounts for primary
emissions of diesel PM only; the contribution of secondary aerosols is
not included.
Dispersion models estimate ambient levels of PM at a receptor site
on the basis of emission factors for the relevant sources and the
investigator's ability to model the advection, mixing, deposition, and
chemical transformation of compounds from the source to the receptor
site. Dispersion models can provide the ability to distinguish on-
highway from off-highway diesel source contributions and can be used to
estimate the concentrations of secondary aerosols from diesel exhaust.
Dispersion modeling is being conducted by EPA to estimate county-
specific concentrations of, and exposures to, several toxic species,
including diesel PM. Results from this model are expected in 2000.
Elemental carbon is a major component of diesel exhaust,
contributing approximately 60-80 percent of diesel particulate mass,
depending on engine technology, fuel type, duty cycle, lube oil
consumption, and state of engine maintenance.\47\ \48\ \49\ \50\ In
most ambient environments, diesel PM is one of the major contributors
to elemental carbon, with other potential sources including gasoline
exhaust; combustion of coal, oil, or wood; charbroiling; cigarette
smoke; and road dust. Because of the large portion of elemental carbon
in diesel PM, and the fact that diesel exhaust is one of the major
contributors to elemental carbon in most ambient environments, diesel
PM concentrations can be bounded using elemental carbon measurements.
One approach for calculating diesel PM concentrations from elemental
carbon measurements is presented in the draft Health Assessment
Document for Diesel Emissions. The surrogate diesel PM calculation is a
useful approach for estimating diesel PM in the absence of a more
sophisticated modeling analysis for locations where elemental carbon
concentrations are available.
---------------------------------------------------------------------------

\47\ Zaebst, D.D., Clapp D.E., Blake L.M., Marlow D.A.,
Steenland K., Hornung R.W., Scheutzle D. and J. Butler (1991)
Quantitative Determination of Trucking Industry Workers Exposures to
Diesel Exhaust Particles. Am. Ind. Hyg. Assoc. J., 52:529-541.
\48\ Graboski, M. S., McCormick, R.L., Yanowitz, J., and L.B.A.
Ryan (1998) Heavy-Duty Diesel Testing for the Northern Front Range
Air Quality Study. Colorado Institute for Fuels and Engine Research.
\49\ Warner-Selph, M. A., Dietzmann, H.E. (1984)
Characterization of Heavy-Duty Motor Vehicle Emissions Under
Transient Driving Conditions. Southwest Research Institute. EPA-600/
3-84-104.
\50\ Pierson, W.R., Brachazek, W. W. (1983) Particulate Matter
Associated with Vehicles on the Road. Aerosol Sci. & Tech. 2:1-40.
---------------------------------------------------------------------------

Ambient concentrations of diesel PM reported for the period before
1990 when no nationwide PM controls were in place for HDVs suggest that
annually averaged diesel PM levels in urban and suburban environments
ranged from approximately 1.9 to 11.6 micrograms/m³ (Table
II.C-3a and Table II.C-3b). On individual days, diesel PM
concentrations as high as 22 micrograms/m³ were reported.
Studies reporting annual average diesel PM concentrations in urban and
suburban areas after 1990 indicate that diesel PM concentrations range
from approximately 0.5 to 3.6 micrograms/m³, with studies
over short periods amidst dense bus traffic averaging 29.2 micrograms/
m³ and ranging up to 46.7 micrograms/m³ (Table
II.C-3a and Table II.C-3b). Dispersion modeling conducted in Southern
California reported that the highway contribution to the reported
diesel PM levels ranged from 63-89 percent of the total diesel PM
(Table II.C-3b). In the two dispersion model studies reporting diesel
PM in Southern California in August 1987 and September 1996, secondary
formation of diesel PM accounted for 27 percent to 67 percent of the
total diesel PM (Table II.C-3b). Using elemental carbon as a surrogate
for diesel PM suggests that diesel PM concentrations measured in some
urban and rural areas in the 1990s range from approximately 0.4 to 4.5
micrograms/m³ in urban environments and 0.2 to 1.3
micrograms/m³ in rural environments (Table II.C-3c).

Table II.C-3a.--Ambient Diesel PM Concentrations and Contribution to Total Ambient PM10 and PM2.5 From Chemical
Mass Balance Studies
----------------------------------------------------------------------------------------------------------------
Diesel PM2.5 Diesel PM % of
Location Year of sampling g/m³ total PM
----------------------------------------------------------------------------------------------------------------
West LA, CA................................ 1982, annual....................... 4.4 13
Pasadena, CA............................... 1982, annual....................... 5.3 19
Rubidoux, CA............................... 1982, annual....................... 5.4 13
Downtown LA, CA ^a.......................... 1982, annual....................... 11.6 36
Phoenix area, AZ ^b......................... 1989-90, Winter.................... * 4-22 50
Phoenix, AZ ^c.............................. 1994-95, Winter.................... 0-5.3 0-27
California, 15 Air Basins ^d................ 1988-92, annual.................... * 0.2-3.6
Manhattan, NY ^e............................ 1993, Spring, 3 d.................. * 13.2-46.7 31-68
Welby and Brighton, CO ^f................... 1996-97, Winter, 60 d.............. 0-7.3 0-26
----------------------------------------------------------------------------------------------------------------
* PM10. The reader should note that 80-95% of diesel PM is PM2.5.
Not Available.
^a Schauer, J.J., Rogge, W.F., Hildemann, L.M., Mazureik, M.A., Cass, G.R., and B.R.T. Simoneit (1996) Source
Apportionment of Airborne particulate Matter Using Organic Compounds as Tracers. Atmos. Environ. 30(22):3837-
3855.

[[Page 35455]]

^b Chow, J.C., Watson, J.G., Richards, L.W., Haase, D.L., McDade, C., Dietrich, D.L., Moon, D., and C. Sloane
(1991) The 1989-1990 Phoenix PM10 Study. Volume II: Source Apportionment. Final Report. DRI Document No.
8931.6F1, prepared for Arizona Department of Environmental Air Quality, Phoenix, AZ, by Desert Research
Institute, Reno, NV.
^c Maricopa Association of Governments. The 1999 Brown Cloud Project for the Maricopa Association of Governments
Area, Revised Draft Report, November 1999.
^d California Environmental Protection Agency (1998) Report to the Air Resources Board on the Proposed
Identification of Diesel Exhaust as a Toxic Air Contaminant. Appendix III, Part A: Exposure Assessment, April
1998.
^e Wittorff, D.N., Gertler, A.W., Chow, J.C., Barnard, W.R. Jongedyk, H.A. The Impact of Diesel Particulate
Emissions on Ambient Particulate Loadings. Air & Waste Management Association 87th Annual Meeting, Cincinnati,
OH, June 19-24, 1994.
^f Fujita, E., Watson, J.G., Chow, J.C., Robinson, N.F., Richards, L.W., Kumar, N. (1998) The Northern Front Rage
Air Quality Study Final Report Volume C: Source Apportionment and Simulation Methods and Evaluation. http://
nfraqs.cira.colostate.edu/

Table II.C-3b.--Ambient Diesel PM Concentrations and Contribution to Total Ambient PM2.5 From Dispersion
Modeling Studies
----------------------------------------------------------------------------------------------------------------
Diesel PM2.5 Diesel PM % of
Location Year of sampling /m³ total PM
----------------------------------------------------------------------------------------------------------------
Azusa, CA.................................. 1982, annual....................... ** 1.4 5
Pasadena, CA............................... 1982, annual....................... ** 2.0 7
Anaheim, CA................................ 1982, annual....................... ** 2.7 12
Long Beach, CA............................. 1982, annual....................... ** 3.5 13
Downtown LA, CA............................ 1982, annual....................... ** 3.5 11
Lennox, CA................................. 1982, annual....................... ** 3.8 13
West LA, CA ^a.............................. 1982, annual....................... ** 3.8 16
Claremont, CA ^b............................ 18-19 Aug 1987..................... 2.4 8
Long Beach, CA............................. 24 Sept 1996....................... ⁺1.9(2.6) 8
Fullerton, CA.............................. 24 Sept 1996....................... ⁺ 2.4(3.9) 9
Riverside, CA ^c............................ 25 Sept 1996....................... ⁺ 4.4(13.3) 12
----------------------------------------------------------------------------------------------------------------
⁺ Value in parenthesis includes secondary diesel PM (nitrate, ammonium, sulfate and hydrocarbons) due to
atmospheric reactions of primary diesel emissions of NO_X, SO2 and hydrocarbons.
** On-road diesel vehicles only; All other values are for on-road plus nonroad diesel emissions.
^a Cass, G.R. and H.A. Gray (1995) Regional Emissions and Atmospheric Concentrations of Diesel Engine Particulate
Matter: Los Angeles as a Case Study. In: Diesel Exhaust: A Critical Analysis of Emissions, Exposure, and
Health Effects. A Special Report of the Institute's Diesel Working Group. Health Effects Institute, Cambridge,
MA, pp. 125-137.
^b Kleeman, M.J., Cass, G.R. (1999a) Identifying the Effect of Individual Emissions Sources on Particulate Air
Quality Within a Photochemical Aerosol Processes Trajectory Model. Atmos. Eviron. 33:4597-4613.
^c Kleeman, M.J., Hughes, L.S., Allen, J.O., Cass, G.R. (1999b) Source Contributions to the Size and Composition
Distribution of Atmospheric Particles: Southern California in September 1996. Environ. Sci. Technol. 33:4331-
4351.

Table II.C-3c.--Ambient Diesel PM Concentrations and Contribution to Total Ambient PM2.5 From Elemental Carbon
Measurements
----------------------------------------------------------------------------------------------------------------
Diesel PM2.5
Location Year of sampling g/ Diesel PM % of
m\3\ total PM
----------------------------------------------------------------------------------------------------------------
Boston, MA................................. 1995, annual....................... 0.7-1.7 3-15
Rochester, NY.............................. 1995, annual....................... 0.4-0.8 2-9
Quabbin, MA................................ 1995, annual....................... 0.2-0.6 1-6
Reading, MA................................ 1995, annual....................... 0.4-1.3 2-7
Brockport, NY ^a............................ 1995, annual....................... 0.2-0.5 1-5
Washington, DC ^b........................... 1992-1995, annual.................. 1.3-1.8 6-10
South Coast Air Basin ^c.................... 1995-1996, annual.................. 2.4-4.5
----------------------------------------------------------------------------------------------------------------
The Multiple Air Toxics Exposure Study in the South Coast Air Basin reported average annual values for 8 sites
in the South Coast Basin.
Not Available.
^a Salmon, L.G., Cass, G.R., Pedersen, D.U., Durant, J.L., Gibb, R., Lunts, A., and M. Utell (1997) Determination
of fine particle concentration and chemical composition in the northeastern United States, 1995. Progress
Report to Northeast States for Coordinated Air Use Management (NESCAUM), September 1999.
^b Sisler, J.F. (1996) Spatial and Seasonal Patterns and Long Term Variability of the Composition of the Haze in
the United States: An Analysis of Data from the IMPROVE Network. Cooperative Institute for Research in the
Atmosphere. Colorado State University. ISSN: 0737-5352-32.
^c South Coast Air Quality Management District (2000) Multiple Air Toxics Exposure Study in the South Coast Air
Basin (MATES-II), Final Report and Appendices, March 2000.

The city-specific emission inventory analysis and independent
investigations of ambient PM2.5 summarized here indicate
that the contribution of diesel engines to PM inventories in several
urban areas around the U.S. is much higher than indicated by the
national PM emission inventories only. One possible explanation for
this is the concentrated use of diesel engines in certain local or
regional areas which is not well represented by the national, yearly
average presented in national PM emission inventories. Another reason
may be underestimation of the in-use diesel PM emission rates. Our
current modeling incorporates deterioration only as would be
experienced in properly maintained, untampered vehicles. We are
currently in the process of reassessing the rate of in-use
deterioration of diesel engines and vehicles which could greatly
increase the contribution of HDVs to diesel PM.
Moreover, heavy-duty vehicles will have a more important
contributing role in ambient PM2.5 concentrations than in
ambient PM10 concentrations. In addition, the absolute
contribution from heavy-duty vehicles is larger in relationship to the
numerically lower PM2.5 standard, making them more

[[Page 35456]]

important to attainment and maintenance.
3. Environmental Justice
Environmental justice is a priority for EPA. The Federal government
documented its concern over this issue through issuing Executive Order
12898, Federal Actions To Address Environmental Justice in Minority
Populations and Low-Income Populations (February 11, 1994). This Order
requires that federal agencies make achieving environmental justice
part of their mission. Similarly, the EPA created an Office of
Environmental Justice (originally the Office of Environmental Equity)
in 1992, commissioned a task force to address environmental justice
issues, oversees a Federal Advisory Committee addressing environmental
justice issues (the National Environmental Justice Advisory Council),
and has developed an implementation strategy as required under
Executive Order 12898.
Environmental justice is a movement promoting the fair treatment of
people of all races, income, and culture with respect to the
development, implementation, and enforcement of environmental laws,
regulations, and policies. Fair treatment implies that no person or
group of people should shoulder a disproportionate share of any
negative environmental impacts resulting from the execution of this
country's domestic and foreign policy programs.
For the last several years, environmental organizations and
community-based citizens groups have been working together to phase out
diesel buses in urban areas. For example, the Natural Resources Defense
Council initiated a ``Dump Dirty Diesel'' campaign in the mid-1990s to
press for the phase out of diesel buses in New York City. Other
environmental organizations operating in major cities such as Boston,
Newark, and Los Angeles have joined this campaign. The Coalition for
Clean Air worked with NRDC and other experts to perform exposure
monitoring in communities located near distribution centers where
diesel truck traffic is heavy. These two organizations concluded that
facilities with heavy truck traffic are exposing local communities to
diesel exhaust concentrations far above the average levels in outdoor
air. The report states: ``These affected communities, and the workers
at these distribution facilities with heavy diesel truck traffic, are
bearing a disproportionate burden of the health \51\^-\62\
risks.'' \63\ Other diesel ``hot spots'' identified by the groups are
bus terminals, truck and bus maintenance facilities, retail
distribution centers, and busy streets and highways.
---------------------------------------------------------------------------

\51\^-\62\ [Reserved]
\63\ Exhausted by Diesel: How America's Dependence on Diesel
Engines Threatens Our Health, Natural Resources Defense Council,
Coalition for Clean Air, May 1998.
---------------------------------------------------------------------------

Although the new standards proposed in this rulemaking would not
reroute heavy-duty truck traffic or relocate bus terminals, they would
be expected to improve air quality across the country and would provide
increased protection to the public against a wide range of health
effects, including chronic bronchitis, respiratory illnesses, and
aggravation of asthma symptoms. These air quality and public health
benefits could be expected to mitigate some of the environmental
justice concerns related to heavy-duty vehicles since the proposal
would provide relatively larger benefits to heavily impacted areas.

D. Anticipated Emissions Benefits

This subsection presents the emission benefits we anticipate from
heavy-duty vehicles as a result of our proposed NO_X, PM, and
NMHC emission standards for heavy-duty engines. The graphs and tables
that follow illustrate the Agency's projection of future emissions from
heavy-duty vehicles for each pollutant. The baseline case represents
future emissions from heavy-duty vehicles at present standards
(including the MY2004 standards). The controlled case quantifies the
future emissions of heavy-duty vehicles if the new standards proposed
in this rulemaking are finalized and implemented.
1. NO_X Reductions
The Agency expects substantial NO_X reductions on both a
percentage and a tonnage basis from this proposal. As illustrated in
the following graph, the air quality benefit expected from this
proposal is a reduction in NO_X emissions from HDVs of 2.0
million tons in 2020.\64\ The Draft RIA provides additional projections
between 2007 and 2030. As stated previously, HDVs contribute about 15
percent to the national NO_X inventory for all sources. The
NO_X standards proposed in this rule would have a substantial
impact on the total NO_X inventory so that in 2030, HDVs
under today's proposed standards would account for only 3 percent of
the national NO_X inventory. Figure II.D-1 shows our national
projections of total NO_X emissions with and without the
proposed engine controls. This includes both exhaust and crankcase
emissions. The proposed standards should result in about a 90 percent
reduction in NO_X from new engines.\65\
---------------------------------------------------------------------------

\64\ The baseline used for this calculation is the 2004 HDV
standards (64 FR 58472). These reductions are in addition to the
NO_X emissions reductions projected to result from the
2004 HDV standards.
\65\ We include in the NO_X projections excess
emissions, developed by the EPA's Office of Enforcement and
Compliance, that were emitted from many model year 1988-98 diesel
engines. This is described in more detail in Chapter 2 of the draft
RIA.

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[[Page 35457]]

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2. PM Reductions
As stated previously, HDVs contribute about 14 percent to the
national PM10 inventory for mobile sources. The 90 percent
reduction in the PM standard for HDVs proposed in this rule would have
a substantial impact on the mobile source PM inventory, so that in 2030
HDVs under today's proposed standards would account for only 3 percent
of the national mobile source PM inventory.
The majority of the projected PM reductions are directly a result
of the proposed exhaust PM standard. However, a modest amount of PM
reductions would come from reducing sulfur in the fuel. For the
existing fleet of heavy-duty vehicles, a small fraction of the sulfur
in diesel fuel is emitted directly into the atmosphere as direct
sulfate, and a portion of the remaining fuel sulfur is transformed in
the atmosphere into sulfate particles, referred to as indirect sulfate.
Reducing sulfur in the fuel decreases the amount of direct sulfate PM
emitted from heavy-duty diesel engines and the amount of heavy-duty
diesel engine SO_X emissions that are transformed into
indirect sulfate PM in the atmosphere.\66\ For engines meeting the
proposed standards, we consider low sulfur fuel to be necessary to
enable the PM control technology. In other words, we do not claim an
additional benefit beyond the proposed standard for reductions in
direct sulfate PM. However, once the proposed low sulfur fuel
requirements go into effect, pre-2007 model year engines would also be
using low sulfur fuel. Because these engines would be certified with
high sulfur fuel, they would achieve reductions in PM beyond their
certification levels.
---------------------------------------------------------------------------

\66\ Sulfate forms a significant portion of total fine
particulate matter in the Northeast. Chemical speciation data in the
Northeast collected in 1995 shows that the sulfate fraction of fine
particulate matter ranges from 20 and 27 percent of the total fine
particle mass. Determination of Fine Particle and Coarse Particle
Concentrations and Chemical Composition in the Northeastern United
States, 1995, NESCAUM, prepared by Cass, et al., September 1999.
---------------------------------------------------------------------------

Figure II.D-2 shows our national projections of total HDV PM
emissions with and without the proposed engine controls. This figure
includes crankcase emissions and the direct sulfate PM benefits due to
the use of low sulfur fuel by the existing fleet. These direct sulfate
PM benefits from the existing fleet are also graphed separately. The
proposed standards should result in about a 90 percent reduction in
total PM from new engines. The proposed low sulfur fuel should result
in about a 95 percent reduction in direct sulfate PM from pre-2007
engines. Due to complexities of the conversion and removal processes of
sulfur dioxide, we do not attempt to quantify the indirect sulfate
reductions that would be derived from this rulemaking. Nevertheless,
the Agency believes that these indirect sulfate PM reductions are
likely to contribute significant additional benefits to public health
and welfare. The air quality benefit of the new PM standards and low
sulfur diesel fuel are presented in Figure II.D-2, indicating a 83,000
ton direct PM reduction in 2020.

[[Page 35458]]

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3. NMHC Reductions
The standards described in section III are designed to be feasible
for both gasoline and diesel heavy-duty vehicles. The NMHC standards
are expected to be more of a challenge for the gasoline vehicles than
for the diesel vehicles, however. (The converse is true for the PM
standards.) Based on our analysis of the aftertreatment technology
described in section III, diesel engines meeting the proposed PM
standard are expected to have NMHC emissions levels well below the
standard in use. Furthermore, although the proposed standards give
manufacturers the same phase-in for NMHC as for NO_X, we
model the NMHC reductions for diesel vehicles to be fully in place in
2007. We believe the use of aftertreatment for PM control would cause
the NMHC levels to be below the proposed standards as soon as the PM
standard goes into effect in 2007. We request comment on this
assumption.
HDVs account for about 3 percent of national VOC and 8 percent from
mobile sources in 2007. Figure II.D-3 shows our national projections of
total NMHC emissions with and without the proposed engine controls.
This includes both exhaust emissions and evaporative emissions. As
presented in Figure II.D-3, the Agency projects a reduction of 230,000
tons of NMHC in 2020 due to the proposed standards.

[[Page 35459]]

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BILLING CODE 6560-50-C
4. Additional Emissions Benefits
This subsection looks at tons/year emission inventories of CO,
SO_X, and air toxics from HDEs. Although we are not including
stringent standards for these pollutants in our proposed standards, we
believe the proposed standards would result in reductions in CO,
SO_X, and air toxics. Here, we present our anticipated
benefits.

a. CO Reductions

In 2007, HDVs are projected to contribute to approximately 5
percent of national CO and 9 percent of CO from mobile sources.
Although it does not propose new CO emission standards, today's
proposal would nevertheless be expected to result in a considerable
reduction in CO emissions from heavy-duty vehicles. CO emissions from
heavy-duty diesel vehicles, although already very low, would likely be
reduced by an additional 90 percent due to the presence of
aftertreatment devices. CO emissions from heavy-duty gasoline vehicles
would also likely decline as the NMHC emissions are decreased. Table
II.D-1 presents the projected reductions in CO emissions from HDVs.

Table II.D-1.--Estimated Reductions in CO
------------------------------------------------------------------------
CO benefit (thousand short
Calendar year tons)
------------------------------------------------------------------------
2007...................................... 71
2010...................................... 405
2015...................................... 911
2020...................................... 1,250
2030...................................... 1,640
------------------------------------------------------------------------

b. SO_X Reductions

HDVs are projected to emit approximately 0.5 percent of national
SO_X and 7 percent of mobile source SO_X in 2007.
We are proposing significant reductions in diesel fuel sulfur to enable
certain emission control devices to function properly. We expect
SO_X emissions to decline as a direct benefit of low sulfur
diesel fuel. The majority of these benefits would be from heavy-duty
highway diesel vehicles; however, some benefits would also come from
highway fuel burned in other applications. As discussed in greater
detail in the section on PM reductions, the amount of sulfate particles
(direct and indirect) formed as a result of diesel exhaust emissions
would decline for all HD diesel engines operated on low sulfur diesel
fuel, including the current on-highway HD diesel fleet, and those non-
road HD diesel engines that may operate on low sulfur diesel fuel in
the future. Table II.D-2 presents our estimates of SO_X
reductions resulting from the proposed low sulfur fuel.

Table II.D-2.--Estimated Reductions in SO_X Due to Low Sulfur Fuel
------------------------------------------------------------------------
SO_X
benefit
Calendar year (thousand
short
tons)
------------------------------------------------------------------------
2007........................................................ 101
2010........................................................ 106
2015........................................................ 115
2020........................................................ 124
2030........................................................ 139
------------------------------------------------------------------------

c. Air Toxics Reductions

This proposal establishes new hydrocarbon and formaldehyde
standards for heavy-duty vehicles. Hydrocarbons are a broad class of
chemical compounds containing carbon and hydrogen. Many forms of
hydrocarbons, such as formaldehyde, are directly hazardous and
contribute to what are collectively called ``air toxics.'' Air toxics
are pollutants known to cause or suspected of causing cancer or other
serious human health effects or ecosystem damage. The Agency has
identified as least 20 compounds emitted from on-road gasoline vehicles
that have toxicological potential, 19 of which are emitted by diesel
vehicles as well as an additional 20 compounds which have been listed
as toxic air

[[Page 35460]]

contaminants by California ARB.\67\ \68\ This proposal also seeks to
reduce emissions of diesel exhaust and diesel particulate matter (see
section II.B for a discussion of health effects).
---------------------------------------------------------------------------

\67\ National Air Quality and Emissions Trends Report, 1997,
(EPA 1998), p. 74.
\68\ California Environmental Protection Agency (1998) Report to
the Air Resources Board on the Proposed Identification of Diesel
Exhaust as a Toxic Air Contaminant, Appendix III, Part A: Exposure
Assessment, April 1998.
---------------------------------------------------------------------------

Our assessment of heavy-duty vehicle (gasoline and diesel) air
toxics focuses on the following compounds with cancer potency estimates
that have significant emissions from heavy-duty vehicles: benzene,
formaldehyde, acetaldehyde, and 1,3-butadiene. These compounds are an
important, but limited, subset of the total number of air toxics that
exist in exhaust and evaporative emissions from heavy-duty vehicles.
The reductions in air toxics quantified in this section represent only
a fraction of the total number and amount of air toxics reductions
expected from the proposed new hydrocarbon standards.
For this analysis, we estimate that air toxic emissions are a
constant fraction of hydrocarbon exhaust emissions. Because air toxics
are a subset of hydrocarbons, and new emission controls are not
expected to preferentially control one type of air toxic over another,
the selected air toxics chosen for this analysis are expected to
decline by the same percentage amount as hydrocarbon exhaust emissions.
We have not performed a separate analysis for the new formaldehyde
standard since compliance with the hydrocarbon standard should result
in compliance with the formaldehyde standard for all petroleum-fueled
engines. The Draft RIA provides more detail on this analysis. Table
II.D-3 shows the estimated air toxics reductions associated with the
anticipated reductions in hydrocarbons.

Table II.D-3.--Estimated Reductions in Air Toxics
[Short tons]
----------------------------------------------------------------------------------------------------------------
1,3-
Calendar year Benzene Formaldehyde Acetaldehyde Butadiene
----------------------------------------------------------------------------------------------------------------
2007...................................................... 153 831 318 65
2010...................................................... 932 4,750 1,870 382
2015...................................................... 2,080 11,400 4,460 909
2020...................................................... 2,780 15,800 6,120 1,250
2030...................................................... 3,510 20,500 7,850 1,600
----------------------------------------------------------------------------------------------------------------

E. Clean Heavy-Duty Vehicles and Low-Sulfur Diesel Fuel Are Critically
Important for Improving Human Health and Welfare

Despite continuing progress in reducing emissions from heavy-duty
engines, emissions from these engines continue to be a concern for
human health and welfare. Ozone continues to be a significant public
health problem, and affects not only people with impaired respiratory
systems, such as asthmatics, but healthy children and adults as well.
Ozone also causes damage to plants and has an adverse impact on
agricultural yields. Diesel exhaust also continues to be a significant
public health concern.
Today's proposal would reduce NO_X, VOC, CO, PM, and
SO_X emissions from these heavy-duty vehicles substantially.
These reductions would help reduce ozone levels nationwide and reduce
the frequency and magnitude of predicted exceedances of the ozone
standard. These reductions would also help reduce PM levels, both by
reducing direct PM emissions and by reducing emissions that give rise
to secondary PM. The NO_X and SO_X reductions would
help reduce acidification problems, and the NO_X reductions
would help reduce eutrophication problems. The PM and NO_X
standard proposed today would help improve visibility. All of these
reductions could be expected to have a beneficial impact on human
health and welfare by reducing exposure to ozone, PM, and other air
toxics and thus reducing the cancer and noncancer effects associated
with exposure to these substances.

III. Heavy-Duty Engine and Vehicle Standards

In this section, we describe the vehicle and engine standards we
are proposing today to respond to the serious air quality needs
discussed in section II. Specifically, we discuss:
The CAA and why we are proposing new heavy-duty standards.
The technology opportunity for heavy-duty vehicles and
engines.
Our proposed HDV and HDE standards, and our proposed
phase-in of those standards.
Why we believe the stringent standards being proposed
today are feasible in conjunction with the low-sulfur gasoline required
under the recent Tier 2 rule and the low-sulfur diesel fuel being
proposed today.
The effects of diesel fuel sulfur on the ability to meet
the proposed standards, and what happens if high sulfur diesel fuel is
used.
A possible reassessment of the technology and diesel fuel
sulfur level needed for diesels to comply with today's proposed
NO_X standard.
We welcome comment on the levels and timing of the proposed
emissions standards, and on the technological feasibility discussion
and supporting analyses. We also request comment on the timing of the
proposed diesel fuel standard in conjunction with these proposed
emission standards. We ask that commenters provide any technical
information that supports the points made in their comments.

A. Why Are We Setting New Heavy-Duty Standards?

We are proposing heavy-duty vehicle and engine standards and
related provisions under section 202(a)(3) of the CAA which authorizes
EPA to establish emission standards for new heavy-duty motor vehicles
(see 42 U.S.C. 7521(a)(3)). Section 202(a)(3)(A) requires that such
standards ``reflect the greatest degree of emission reduction
achievable through the application of technology which the
Administrator determines will be available for the model year to which
such standards apply, giving appropriate consideration to cost, energy,
and safety factors associated with the application of such
technology.'' Section 202(a)(3)(B) allows EPA to take into account air
quality information in revising such standards. Because heavy-duty
engines contribute greatly to a number of serious air pollution
problems, especially the health and welfare effects of ozone, PM, and
air toxics, and because millions of Americans live in areas that exceed
the

[[Page 35461]]

national air quality standards for ozone or PM, we believe the air
quality need for tighter heavy-duty standards is well founded. This,
and our belief that a significant degree of emission reduction from
heavy-duty vehicles and engines is achievable through the application
of new diesel emission control technology, further refinement of well
established gasoline emission controls, and reductions of diesel fuel
sulfur levels, leads us to believe that new emission standards are
warranted.

B. Technology Opportunity for Heavy-Duty Vehicles and Engines

For the past 30 or more years, emission control development for
gasoline vehicles and engines has concentrated most aggressively on
exhaust emission control devices. These devices currently provide as
much as or more than 95 percent of the emission control on a gasoline
vehicle. In contrast, the emission control development work for diesels
has concentrated on improvements to the engine itself to limit the
emissions leaving the combustion chamber.
However, during the past 15 years, more development effort has been
put into diesel exhaust emission control devices, particularly in the
area of PM control. Those developments, and recent developments in
diesel NO_X control devices, make the advent of diesel
exhaust emission controls feasible. Through use of these devices, we
believe emission control similar to that attained by gasoline
applications will be possible with diesel applications. However,
without low-sulfur diesel fuel, these technologies cannot be
implemented on heavy-duty or light-duty diesel applications.
Several exhaust emission control devices have been developed to
control harmful diesel PM constituents--the diesel oxidation catalyst
(DOC), and the many forms of particulate filters, or traps. DOCs have
been shown to be durable in use, but they control only a relatively
small fraction of the total PM and, consequently, do not address our PM
concerns sufficiently. Uncatalyzed diesel particulate traps
demonstrated high efficiencies many years ago, but the level of the PM
standard was such that it could be met through less costly ``in-
cylinder'' control techniques. Catalyzed diesel particulate traps have
the potential to provide major reductions in diesel PM emissions and
provide the durability and dependability required for diesel
applications. Therefore, as discussed in the feasibility portion of
this section, at this time we believe the catalyzed PM trap will be the
control technology of choice for future control of diesel PM emissions.
However, as discussed in detail in the draft RIA, we believe that
catalyzed PM traps cannot be brought to market on diesel applications
unless low-sulfur diesel fuel is available.
Diesel NO_X control is arguably at an earlier stage of
development than is diesel PM control. Even so, several exhaust
emission control technologies are being developed to control
NO_X emissions, and the industry seems focused on a couple of
these as the most promising technologies for enabling lower
NO_X emission standards. Diesel selective catalytic
reduction, or SCR, has been developed to the point of nearing market
introduction in Europe. SCR has significant NO_X control
potential, but it also has many roadblocks to marketability in this
country. These roadblocks, discussed in more detail in the draft RIA,
include infrastructure issues that we believe would prove exceedingly
difficult and potentially costly to overcome. Because of that, we
believe that the NO_X adsorber is the best technology for
delivering significant diesel NO_X reductions while also
providing market and operating characteristics necessary for the U.S.
market.\69\ However, as is discussed in detail in the draft RIA, the
NO_X adsorber, like the catalyzed PM trap, cannot be brought
to market on diesel applications unless low-sulfur diesel fuel is
available.
---------------------------------------------------------------------------

\69\ The NO_X adsorber was originally developed for
stationary source emission control and was subsequently developed
for use in the lean operating environment of gasoline direct
injection engines.
---------------------------------------------------------------------------

Improvements have also been made to gasoline emission control
technology during the past few years, even the past 12 months. Such
improvements include those to catalyst designs in the form of improved
washcoats and improved precious metal dispersion. Much effort has also
been put into improved cold start strategies that allow for more rapid
catalyst light-off. This can be done by retarding the spark timing to
increase the temperature of the exhaust gases, and by using air-gap
manifolds, exhaust pipes, and catalytic converter shells to decrease
heat loss from the system.
These improvements to gasoline emission control have been made in
response to the California LEV-II standards and the federal Tier 2
standards. Some of this development work was contributed by EPA in a
very short timeframe and with very limited resources in support of our
Tier 2 program.\70\ These improvements should transfer well to the
heavy-duty gasoline segment of the fleet. With such migration of light-
duty technology to heavy-duty vehicles and engines, we believe that
considerable improvements to heavy-duty emissions can be realized, thus
enabling much more stringent standards.
---------------------------------------------------------------------------

\70\ See Chapter IV.A of the final Tier 2 Regulatory Impact
Analysis, contained in Air Docket A-97-10.
---------------------------------------------------------------------------

The following discussion provides more detail on the technologies
we believe are most capable of enabling very stringent heavy-duty
emission standards. The goal of this discussion is to highlight the
emission reduction capability of these emission control technologies
and to highlight their critical need for diesel sulfur levels as low as
those being proposed today. But first, we present the details of the
emission standards being proposed today.

C. What Engine and Vehicle Standards Are We Proposing?

1. Heavy-Duty Engine Standards

a. Federal Test Procedure

The emission standards being proposed today for heavy-duty engines
are summarized in Table III.C-1.

Table III.C-1.--Proposed Full Useful Life Heavy-Duty Engine Emission Standards and Phase-Ins
----------------------------------------------------------------------------------------------------------------
Phase-in by model year (In percent)
Standard (g/ -----------------------------------------------
bhp-hr) 2007 2008 2009 2010
----------------------------------------------------------------------------------------------------------------
Diesel........................ NO_X 0.20
NMHC 0.14 25 50 75 100
HCHO 0.016
Gasoline...................... NO_X 0.20
NMHC 0.14 100

[[Page 35462]]

HCHO 0.016
Diesel & Gasoline............. PM 0.01 100
----------------------------------------------------------------------------------------------------------------

With respect to PM, this proposed new standard would represent a 90
percent reduction for most heavy-duty diesel engines from the current
PM standard, which was not proposed to change in model year 2004.\71\
The current PM standard for most heavy-duty engines, 0.1 g/bhp-hr, was
implemented in the 1994 model year; the PM standard for urban buses
implemented in that same year was 0.05 g/bhp-hr. The proposed PM
standard of 0.01 g/bhp-hr is projected to require the addition of a
highly efficient PM trap to diesel engines, including urban buses; it
is not expected to require the addition of any new hardware for
gasoline engines. We request comment on the feasibility and
appropriateness of this proposed PM standard.
---------------------------------------------------------------------------

\71\ From 64 FR 58472, October 29, 1999, ``* * * diesel fuel
quality, and in particular, diesel fuel sulfur level, can play an
important role in enabling certain PM and NO_X control
technologies. Some DOCs and continuously regenerable PM traps, as
well as current generation lean NO_X adsorber catalysts
can be poisoned by high sulfur levels. Given this information, EPA
has not included more stringent PM standards for the 2004 model year
or later in today's proposal.''
---------------------------------------------------------------------------

With respect to NMHC and NO_X, these new standards would
represent roughly a 90 percent reduction in diesel NO_X and
roughly a 70 percent reduction in diesel NMHC levels compared to the
2004 heavy-duty diesel engine standard. The 2004 heavy-duty diesel
engine standard is 2.5 g/bhp-hr NMHC+NO_X, with a cap on NMHC
of 0.5 g/bhp-hr. Like the PM standard, the proposed NO_X
standard is projected to require the addition of highly efficient
NO_X aftertreatment to diesel engines. For gasoline engines,
the standard proposed in the 2004 heavy-duty rule is 1.0 g/bhp-hr
NMHC+NO_X. Therefore, for gasoline engines, the standards
proposed today would represent roughly a 70 percent reduction. We
request comment on the feasibility and appropriateness of these
proposed NO_X and NMHC standards.
With respect to formaldehyde, a hazardous air pollutant that is
emitted by heavy-duty engines and other mobile sources, we are
proposing standards to prevent excessive emissions. The standards are
comparable in stringency to the formaldehyde standards recently
finalized in the Tier 2 rule for passenger vehicles; they are also
consistent with the CARB LEV II formaldehyde standards. These standards
would be especially important for methanol-fueled engines because
formaldehyde is chemically similar to methanol and is one of the
primary byproducts of incomplete combustion of methanol. Formaldehyde
is also emitted by engines using petroleum fuels (i.e., gasoline or
diesel fuel), but to a lesser degree than is typically emitted by
methanol-fueled engines. We recognize that petroleum-fueled engines
able to meet the proposed NMHC standards should comply with the
formaldehyde standards with large compliance margins. Based upon the
analysis of similar standards recently finalized for passenger
vehicles, we believe that formaldehyde emissions from petroleum-fueled
engines when complying with the PM, NMHC, and NO_X standards
should be as much as 90 percent below the standards.\72\ Thus, to
reduce testing costs, we are proposing a provision that would permit
manufacturers of petroleum-fueled engines to demonstrate compliance
with the formaldehyde standards based on engineering analysis. This
provision would require manufacturers to make a demonstration in their
certification application that engines having similar size and emission
control technology have been shown to exhibit compliance with the
applicable formaldehyde standard for their full useful life. This
demonstration would be similar to that recently finalized for light-
duty vehicles to demonstrate compliance with the Tier 2 formaldehyde
standards.
---------------------------------------------------------------------------

\72\ See the Tier 2 Response to Comments document contained in
Air Docket A-97-10.
---------------------------------------------------------------------------

Because the NO_X exhaust emission control technology we
expect would be required to meet the proposed NO_X standard
is at an early stage of development, we believe a phase-in of the
NO_X standard is appropriate. With a phase-in, manufacturers
are able to introduce the new technology on a limited number of
engines, thereby gaining valuable experience with the technology prior
to implementing it on their entire fleet. Also, we are proposing that
the NO_X, HCHO, and NMHC standards be phased-in together for
diesel engines. That is, engines would be expected to meet each of
these proposed new standards, not just one or the other. We propose
this because the standard as proposed in the 2004 heavy-duty rule would
be a combined NMHC+NO_X standard. Separating the phase-ins
for NMHC and NO_X would create a problem because it would not
be clear to what NMHC standard an engine would certify were it to
certify to the proposed NO_X standard independent of
certifying to the proposed NMHC standard (and vice versa for engines
certifying to the proposed NMHC standard independent of the proposed
NO_X standard).\73\ We request comment on the phase-in for
diesel engines of these proposed NO_X, HCHO, and NMHC
standards and the requirement that they be phased-in together. We also
request comment on alternative phase-in schedules and percentages, such
as a phase-in over three years (2007-2009), a phase-in over two years
(2007-2008), and no phase-in (100% in 2007). We are not proposing a
phase-in for gasoline engines because we want to maintain consistency
with the proposed heavy-duty gasoline vehicle standards which are not
phased-in; those standards are discussed below.\74\ Nonetheless, we
request comment on possible alternative phase-ins for the proposed
gasoline engine standards, such as a phase-in consistent with the
proposed phase-in for diesel engine standards shown in Table III.C-

[[Page 35463]]

1, or a phase-in consistent with that used for heavy light-duty trucks
and medium-duty passenger vehicles under the light-duty highway Tier 2
program.
---------------------------------------------------------------------------

\73\ Note that, despite the concurrent phase-in of
NO_X and NMHC standards for diesel engines, the NMHC
standards should be easily met through use of a PM trap as is fully
discussed in section III.E. Since the PM standards would be
implemented on 100 percent of new engines in the 2007 model year,
all new engines would have a PM trap and would, therefore, control
NMHC emissions to levels below the proposed standards. Therefore,
while the NMHC standard is phased-in with NO_X due to the
2004 combining of the NO_X and NMHC standards, the
proposed NMHC standards would be met by all new engines in the 2007
model year. This is reflected in our emission inventory analysis as
was discussed in section II.
\74\ Please refer to section III.D.2 below for a discussion of
implementing these proposed standards in the 2007 or 2008 model
years, and the relationship between today's proposed implementation
and the implementation of the proposed 2004 emission standards.
---------------------------------------------------------------------------

The specifics of the Averaging, Banking, and Trading program
associated with today's proposed standards are discussed in section VII
of this preamble. The reader should refer to that section for more
details.

b. Not-to-Exceed and Supplemental Steady-State Test

To help ensure that heavy-duty engine emissions are controlled over
the full range of speed and load combinations commonly experienced in
use, we have previously proposed to apply Not-To-Exceed (NTE) limits to
heavy-duty diesel engines (64 FR 58472, October 29, 1999). As proposed,
the NTE approach establishes an area (the ``NTE zone'') under the
torque curve of an engine where emissions must not exceed a specified
value for any of the regulated pollutants.\75\ As proposed, the
specified value under which emissions must remain is 1.25 times the FTP
standards. The NTE standard would apply under any conditions that could
reasonably be expected to be seen by that engine in normal vehicle
operation and use. In addition, we have proposed that the whole range
of real ambient conditions be included in NTE testing.
---------------------------------------------------------------------------

\75\ Torque is a measure of rotational force. The torque curve
for an engine is determined by an engine ``mapping'' procedure
specified in the Code of Federal Regulations. The intent of the
mapping procedure is to determine the maximum available torque at
all engine speeds. The torque curve is merely a graphical
representation of the maximum torque across all engine speeds.
---------------------------------------------------------------------------

Similarly, to help ensure that heavy-duty engine emissions are
controlled during steady-state type driving (such as a line-haul truck
operating on a freeway), we have previously proposed a new supplemental
steady-state test (64 FR 58472, October 29, 1999). The supplemental
steady-state test consists of 13 steady-state modes, each weighted
according to the amount of time that might be expected at each mode
during typical real world conditions. As proposed, the supplemental
steady-state test has emission limits of 1.0 times the FTP standards.
Today's document proposes to apply the heavy-duty diesel NTE and
supplemental steady-state test provisions intended to be finalized as
part of the 2004 standards rulemaking. The October 29, 1999, proposal
for that rule contained the description of these provisions. We expect
that a number of modifications will be made to those provisions in the
FRM for that rule based on feedback received during the comment period.
While the details of the final provisions are not yet available, we
will provide the necessary information in the docket for this rule as
soon as it becomes available in order to allow for comment.
We have not proposed that the NTE requirements, or the supplemental
steady-state test, apply to heavy-duty gasoline engines. However, we
are working with several industry members to pursue a proposal in a
separate action with the intention of having NTE requirements in place
for heavy-duty gasoline engines beginning in the 2004 model year.\76\
Today's proposal intends that those provisions, when developed, would
apply to the gasoline engines subject to today's proposed standards as
well. We currently have no intention of pursuing supplemental steady-
state test requirements for heavy-duty gasoline engines.
---------------------------------------------------------------------------

\76\ Letters from Margo Oge, EPA, to Kelly Brown, Ford Motor
Company, and Samuel. Leonard, General Motors Corp., both dated
September 17, 1999; and letter from Samuel. Leonard, GM, and Kelly
Brown, Ford, to Margo Oge, EPA, dated August 10,1999; all of these
letters are available in EPA Air Docket #A-98-32.
---------------------------------------------------------------------------

We request comment and data on the feasibility of technology
meeting the proposed emission standards in the context of the NTE and
supplemental steady-state tests as proposed in the 2004 heavy-duty
rule, and the potential changes to the supplemental tests should
changes be made from what was proposed. As stated above, should such
changes be made, we will provide the necessary information in the
docket for this rule as soon as it becomes available in order to allow
for comment.

c. Crankcase Emissions Control

Crankcase emissions are the pollutants that are emitted in the
gases that are vented from an engine's crankcase. These gases are also
referred to as ``blowby gases'' because they result from engine exhaust
from the combustion chamber ``blowing by'' the piston rings into the
crankcase. These gases are vented to prevent high pressures from
occurring in the crankcase. Our existing emission standards prohibit
crankcase emissions from all highway engines except turbocharged heavy-
duty diesel engines. The most common way to eliminate crankcase
emissions has been to vent the blowby gases into the engine air intake
system, so that the gases can be recombusted. We made the exception for
turbocharged heavy-duty diesel engines because of concerns in the past
about fouling that could occur by routing the diesel particulates
(including engine oil) into the turbocharger and aftercooler. Our
concerns are now alleviated by newly developed closed crankcase
filtration systems, specifically designed for turbocharged heavy-duty
diesel engines. These new systems (discussed more fully in section
III.E and in Chapter III of the draft RIA) are already required for new
on-highway diesel engines under the EURO III emission standards.
We are proposing to eliminate the exception for turbocharged heavy-
duty diesel engines starting in the 2007 model year. This is an
environmentally significant proposal since most heavy-duty diesel
trucks use turbocharged engines, and a single engine can emit over 100
pounds of NO_X, NMHC, and PM from the crankcase over the
lifetime of the engine. We request comment on this proposal.
2. Heavy-Duty Vehicle Standards

a. Federal Test Procedure

The emission standards being proposed today for heavy-duty vehicles
are summarized in Table III.C-2. We have already proposed that all
complete heavy-duty gasoline vehicles, whether for transporting
passengers or for work, be chassis certified (64 FR 58472, October 29,
1999). Current federal regulations do not require that complete diesel
vehicles over 8,500 pounds be chassis certified, instead requiring
certification of their engines. Today's proposal does not make changes
to those requirements.
The Tier 2 final rule created a new vehicle category called
``medium-duty passenger vehicles''.\77\ These vehicles, both gasoline
and diesel, are required to meet requirements of the Tier 2 program,
which carries with it a chassis certification requirement. As a result,
applicable complete diesel vehicles must certify using the chassis
certification test procedure. Today's proposed chassis standards for
2007 and later model year heavy-duty gasoline vehicles would apply to
the remaining (work-oriented) complete gasoline vehicles under 14,000
pounds.
---------------------------------------------------------------------------

\77\ Medium-duty passenger vehicles are defined as any complete
vehicle between 8,500 and 10,000 pounds GVWR designed primarily for
the transportation of persons. The definition specifically excludes
any vehicle that (1) has a capacity of more than 12 persons total
or, (2) is designed to accommodate more than 9 persons in seating
rearward of the driver's seat or, (3) has a cargo box (e.g., pick-up
box or bed) of six feet or more in interior length. (See the Tier 2
final rulemaking, 65 FR 6698, February 10, 2000)

[[Page 35464]]

Table III.C-2.--Proposed 2007+ Full Useful Life Heavy-Duty Vehicle Exhaust Emission Standards for Complete
Gasoline Vehicles*
[grams/mile]
----------------------------------------------------------------------------------------------------------------
Weight range (GVWR) NO_X NMHC HCHO PM
----------------------------------------------------------------------------------------------------------------
8500 to 10,000 lbs.......................................... 0.2 0.195 0.016 0.02
10,000 to 14,000 lbs........................................ 0.4 0.230 0.021 0.02
----------------------------------------------------------------------------------------------------------------
^* Does not include medium-duty passenger vehicles.

These NO_X standards represent a 78 percent reduction and
a 60 percent reduction from the standards for 8,500-10,000 pound and
10,000-14,000 pound vehicles, respectively, proposed in the 2004 heavy-
duty rule. The 2004 heavy-duty rule would require such vehicles to meet
the California LEV-I NO_X standards of 0.9 g/mi and 1.0 g/mi,
respectively. The proposed NO_X standards shown in Table
III.C-2 are consistent with the CARB LEV-II NO_X standard for
low emission vehicles (LEVs). We have proposed, and CARB has put into
place in their LEV-II program, a slightly higher NO_X
standard for 10,000 to 14,000 pound vehicles because these vehicles are
tested at a heavier payload. The increased weight results in using more
fuel per mile than vehicles tested at lighter payloads; therefore, they
tend to emit slightly more grams per mile than lighter vehicles.\78\
---------------------------------------------------------------------------

\78\ Engine standards, in contrast, are stated in terms of grams
per unit power rather than grams per mile. Therefore, engine
emission standards need not increase with weight because heavier
engines do not necessarily emit more per horsepower even though they
tend to emit more per mile.
---------------------------------------------------------------------------

The NMHC standards represent a 30 percent reduction from the
proposed 2004 standards for 8500-10,000 and 10,000-14,000 pound
vehicles. The 2004 heavy-duty rule would require such vehicles to meet
NMHC standard levels of 0.28 g/mi and 0.33 g/mi, respectively (equal to
the California LEV-I nonmethane organic gases (NMOG) standard levels).
The proposed NMHC standards are consistent with the CARB LEV-II NMOG
standards for LEVs in each respective weight class. The NMHC standard
for 10,000-14,000 pound vehicles is higher than for 8,500-10,000 pound
vehicles for the same reason as stated above for the higher
NO_X standard for such vehicles.
The formaldehyde standards are comparable in stringency to the
formaldehyde standards recently finalized in the Tier 2 rule for
passenger vehicles; they are also consistent with today's proposed
engine standards and the CARB LEV II formaldehyde standards.
Formaldehyde is a hazardous air pollutant that is emitted by heavy-duty
vehicles and other mobile sources, and we are proposing these
formaldehyde standards to prevent excessive formaldehyde emissions.
These standards would be especially important for methanol-fueled
vehicles because formaldehyde is chemically similar to methanol and is
one of the primary byproducts of incomplete combustion of methanol.
Formaldehyde is also emitted by vehicles using petroleum fuels (i.e.,
gasoline or diesel fuel), but to a lesser degree than is typically
emitted by methanol-fueled vehicles. We recognize that petroleum-fueled
vehicles able to meet the proposed NMHC standards should comply with
the formaldehyde standards with large compliance margins. Based upon
the analysis of similar standards recently finalized for passenger
vehicles, we believe that formaldehyde emissions from petroleum-fueled
vehicles when complying with the PM, NMHC and NO_X standards
should be as much as 90 percent below the standards.\79\ Thus, to
reduce testing costs, we are proposing a provision that would permit
manufacturers of petroleum-fueled vehicles to demonstrate compliance
with the formaldehyde standards based on engineering analysis. This
provision would require manufacturers to make a demonstration in their
certification application that vehicles having similar size and
emission control technology have been shown to exhibit compliance with
the applicable formaldehyde standard for their full useful life. This
demonstration would be similar to that recently finalized for light-
duty vehicles to demonstrate compliance with the Tier 2 formaldehyde
standards.
---------------------------------------------------------------------------

\79\ See the Tier 2 Response to Comments document contained in
Air Docket A-97-10.
---------------------------------------------------------------------------

The PM standard represents over an 80 percent reduction from the
CARB LEV-II LEV category PM standard of 0.12 g/mi. Note that the PM
standard shown in Table III.C-2 represents not only a stringent PM
level, but a new standard for federal HDVs where none existed before.
The California LEV-II program for heavy-duty vehicles, and the federal
Tier 2 standards for over 8,500 pound vehicles designed for
transporting passengers, both contain PM standards. The PM standard
proposed today is consistent with the Tier 2 bin 8 level of 0.02 g/mi.
The standards shown in Table III.C-2 are, we believe, comparable in
stringency to the proposed diesel and gasoline engine standards shown
in Table III.C-1. We request comment on this issue, including any
supporting data. We also request comment on other possible vehicle
exhaust emission standards. For example, the CARB LEV-II ULEV standards
are identical in NO_X levels, but have NMOG levels of 0.143
and 0.167 g/mi for 8,500 to 10,000 pound and 10,000 to 14,000 pound
vehicles, respectively. We request comment on whether these standards
(0.143 and 0.167 g/mi NMHC for 8,500 to 10,000 pound and 10,000 to
14,000 pound vehicles, respectively), or lower standards, may be more
appropriate emission standards. We also request comment on whether we
should instead include a 40 percent/60 percent split of standards at
the LEV-II LEV and ULEV levels, respectively. To clarify, the CARB LEV-
II program requires a compliance split of vehicles certified to the LEV
versus the ULEV levels; that split is 40 percent LEV and 60 percent
ULEV. We request comment on whether we should employ such a split.
We are not proposing a phase-in for the HDV standards. As proposed,
the HDV standards would apply only to complete gasoline vehicles,
consistent with our current regulations. We believe that emission
control technology for gasoline engines is in an advanced enough state
to justify a simple implementation requirement in the 2007 model year.
However, please refer to section III.D.2, below, for a discussion of
the appropriate implementation schedule associated with these proposed
standards, and the relationship between today's proposed implementation
and the implementation of the proposed 2004 emission standards. We
believe that our proposed implementation schedule provides consistency
with our Tier 2 standards and our expectation of probable certification
levels for similarly sized light-duty trucks and medium-duty

[[Page 35465]]

passenger vehicles. Although these vehicles are allowed to certify at
fairly high emission levels under the Tier 2 bin structure, we believe
that Tier 2 gasoline applications will be designed to certify to
standards of 0.20 g/mi NO_X and 0.09 g/mi NMHC by the 2007
model year, and possibly lower to allow for diesels certifying in
higher emission bins within the NO_X averaging scheme. This
makes the proposed HDV standards and associated phase-in consistent
with Tier 2. We request comment on the appropriateness of not having a
phase-in associated with the vehicle standards. We also request comment
on possible alternative phase-ins for the proposed gasoline vehicle
standards, such as a phase-in consistent with the proposed phase-in for
diesel engine standards shown in Table III.C-1, or a phase-in
consistent with that used for heavy light-duty trucks and medium-duty
passenger vehicles under the light-duty highway Tier 2 program.
Consistent with current regulations, we are not proposing to allow
complete heavy-duty diesel vehicles to certify to the heavy-duty
vehicle standards. Instead, manufacturers would be required to certify
the engines intended for such vehicles to the engine standards shown in
Table III.C-1. However, we request comment on whether complete heavy-
duty diesel vehicles should be allowed, or perhaps should be required,
to certify to the vehicle standards. Any comments on this topic should
also address whether a phase-in, consistent with the phase-in of engine
standards, would be appropriate.
The specifics of the Averaging, Banking, and Trading program
associated with today's proposed standards are discussed in section VII
of this document. The reader should refer to that section for more
details.
We request comment on the feasibility and appropriateness of the
proposed standards for heavy-duty complete vehicles shown in Table
III.C-2.

b. Supplemental Federal Test Procedure

We are not proposing new supplemental FTP (SFTP) standards for
heavy-duty vehicles. The SFTP standards control off-cycle emissions in
a manner analogous to the NTE requirements for engines. We believe that
the SFTP standards are an important part of our light-duty program just
as we believe the NTE requirements will be an important part of our
heavy-duty diesel engine program. Although we are not proposing SFTP
standards for heavy-duty vehicles, we intend to do so via a separate
rulemaking. We request comment on such an approach, and on appropriate
SFTP levels for heavy-duty vehicles along with supporting data.
3. Heavy-Duty Evaporative Emission Standards
We are proposing new evaporative emission standards for heavy-duty
vehicles and engines. The proposed standards are shown in Table III.C-
3. These standards would apply to heavy-duty gasoline-fueled vehicles
and engines, and methanol-fueled heavy-duty vehicles and engines.
Consistent with existing standards, only the standard for the three day
diurnal test sequence would apply to liquid petroleum gas (LPG) fueled
and natural gas fueled HDVs.

Table III.C-3.--Proposed Heavy-Duty Evaporative Emission Standards*
[Grams per test]
------------------------------------------------------------------------
Supplemental
3 day 2 day
Category diurnal + diurnal +
hot soak hot soak**
------------------------------------------------------------------------
8,500-14,000 lbs............................... 1.4 1.75
>14,000 lbs.................................... 1.9 2.3
------------------------------------------------------------------------
^* Proposed to be implemented on the same schedule as the proposed
gasoline engine and vehicle exhaust emission standards shown in Tables
III.C-1 and III.C-2. These proposed standards would not apply to
medium-duty passenger vehicles, and would not apply to diesel fueled
vehicles.
^** Does not apply to LPG or natural gas fueled HDVs.

These proposed standards represent more than a 50 percent reduction
in the numerical standards as they exist today. The 2004 heavy-duty
rule (64 FR 58472, October 29, 1999) proposed no changes to the
numerical value of the standard, but it did propose new evaporative
emission test procedures for heavy-duty complete gasoline vehicles.\80\
Those test procedures would effectively increase the stringency of the
standards, even though the numerical value was not proposed to change.
For establishing evaporative emission levels from complete heavy-duty
vehicles, the standards shown in Table III.C-3 presume the test
procedures proposed in the 2004 heavy-duty rule.
---------------------------------------------------------------------------

\80\ The proposed test procedure changes sought to codify a
commonly approved waiver allowing heavy-duty gasoline vehicles to
use the light-duty driving cycle for demonstrating evaporative
emission compliance. The urban dynamometer driving schedule (UDDS)
used for heavy-duty vehicles is somewhat shorter than that used for
light-duty vehicles, both in terms of mileage covered and minutes
driven. This results in considerably less time for canister purge
under the heavy-duty procedure than under the light-duty procedure.
We recognize this discrepancy and have routinely provided waivers
under the enhanced evaporative program that allow the use of the
light-duty procedures for heavy-duty certification testing. We do
not believe that this approach impacts the stringency of the
standards. Further, it is consistent with CARB's treatment of
equivalent vehicles.
---------------------------------------------------------------------------

The proposed standards for 8,500 to 14,000 pound vehicles are
consistent with the Tier 2 standards for medium-duty passenger vehicles
(MDPV). MDPVs are of consistent size and have essentially identical
evaporative emission control systems as the remaining work-oriented
HDVs in the 8,500 to 10,000 pound weight range. Therefore, the
evaporative emission standards should be equivalent. We are proposing
those same standards for the 10,000 to 14,000 pound HDVs because,
historically, the evaporative emission standards have been consistent
throughout the 8,500 to 14,000 pound weight range. We believe that the
HDVs in the 10,000 to 14,000 pound range are essentially equivalent in
evaporative emission control system design as the lighter HDVs;
therefore, continuing this historical approach is appropriate.
We are proposing slightly higher evaporative emission standards for
the over 14,000 pound HDVs because of their slightly larger fuel tanks
and vehicle sizes. This is consistent with past evaporative emission
standards. The levels chosen for the over 14,000 pound HDVs maintains
the same ratio relative to the 8,500 to 14,000 pound HDVs as exists
with current evaporative standards. To clarify, the current standards
for the 3 day diurnal test are 3 and 4 grams/test for the 8,500 to
14,000 and the over 14,000 pound categories, respectively. The ratio of
3:4 is maintained for the proposed 2007 standards, 1.4:1.9.
The proposed standards levels are slightly higher than the
California LEV-II standards levels. The California standards levels are
1.0 and 1.25 for the 3-day and the 2-day tests, respectively. We
believe that our standards are appropriate for federal vehicles
certified on the higher-volatility federal test fuel.
We are proposing that the proposed evaporative emission standards
be implemented on the same schedule as the proposed gasoline engine and
vehicle exhaust standards shown in Tables III.C-1 and III.C-2. We
request comment on this proposal. Also, we are proposing the revised
durability provisions finalized in the Tier 2 rulemaking, which require
durability demonstration using fuel containing at least 10 percent
alcohol. Alcohol can break down the materials used in evaporative
emission control systems. Therefore, a worst case durability
demonstration would include a worst case alcohol level in the fuel (10
percent) as some areas of the country

[[Page 35466]]

use alcohol fuels to improve their air quality. We request comment on
extending this durability provision to HDVs.
We request comment on the feasibility and appropriateness of the
proposed evaporative emission standards shown in Table III.C-3.

D. Standards Implementation Issues

1. Alternative Approach to Phase-In
Although we are proposing the standards and diesel phase-ins shown
in Section III.C, we request comment on the possibility of structuring
the proposed diesel engine standards as a ``declining'' standard rather
than the standard level ``phase-in'' being proposed. Under such an
approach, the final NO_X and NMHC standards of 0.20 and 0.14
g/bhp-hr would be achieved via a ramping down of the standards from the
NO_X and NMHC levels assumed under the 2004
NMHC+NO_X standard (i.e., 2.0 g NO_X and 0.5 g
NHMC) to the final levels provided it did not compromise the air
quality benefits in any given year. Such a declining standard would
result in 2007 standards for all engines lower than the 2004 standards,
but not as low as today's proposed standards. The 2008 standards for
all engines would then be lower than the 2007 standards, and the 2009
standards for all engines would be lower than the 2008 standards. In
2010, the standards would become 0.20 g/bhr-hr NO_X and 0.14
g/bhp-hr NMHC.
Under such a declining standard approach, an engine manufacturer
would probably have to redesign most, if not all, of its engines to
reduce their emissions from the 2004 standard levels to the 2007 model
year declining standard levels. In contrast, under the proposed
approach, 25 percent of an engine manufacturer's engines would have to
certify to the 0.20/0.14 g/bhp-hr standards. Although the phase-in
levels would be more stringent, the manufacturer would have to redesign
only that 25 percent of its engines during the 2007 model year. The
same would be true for the ensuing years. Under the declining standard
approach, some level of redesign would probably have to be done on
every engine in every year to meet the declining standard unless a
manufacturer had extensive ABT credits at its disposal to apply against
the standard. Under the phase-in, each new model year would entail a
redesign of only 25 percent of a manufacturer's engines. In the end,
both approaches result in the entire fleet meeting the proposed
standard levels in 2010, but both achieve that in different ways.
We request comment on this declining standard approach for the
diesel engine standards. We also request suggestions on appropriate
declining standards for each model year that would result in stringency
levels and emission reductions consistent with those of the proposed
phase-in approach.
We also request comment on the possibility of structuring the
phase-in of the proposed diesel engine standards as a ``cumulative''
phase-in rather than the 25-50-75-100 percent phase-in being proposed.
Under such an approach, a manufacturer could phase-in compliance with
the proposed standards in whatever percentages were most beneficial to
that manufacturer, provided the cumulative total in each year met or
exceeded the cumulative total of the proposed phase-in. Whatever the
phase-in schedule chosen by the manufacturer, all of its engines sold
in model year 2010 would be required to demonstrate compliance with the
proposed standards. For example, a manufacturer could phase-in its
engines according to a schedule of 50-50-50-100 percent, or 35-50-65-
100 percent, or 30-60-60-100, etc. Note that the cumulative percentages
would have to be based on cumulative engine sales to avoid the
possibility that variations in market conditions would not compromise
air quality benefits. We believe that such a phase-in could provide
manufacturers with more flexibility in product planning while possibly
enhancing the air quality benefits of the proposed standards because
some manufacturers may accelerate their phase-in. Manufacturers should
indicate their interest in such an approach in their comments and
should indicate how they might utilize it.
2. Implementation Schedule for Gasoline Engine and Vehicle Standards
The October 1999 proposal of new heavy-duty engine and vehicle
standards included revised standards for gasoline heavy-duty engines
and vehicles (64 FR 58472, October 29, 1999). These standards were
proposed to take effect in the 2004 model year. Commenters on that
proposal raised concerns that these standards could not take effect
until model year 2005 or later because of the applicability of Clean
Air Act section 202(a)(3)(C) to these engines and vehicles. Those
commenters argued that this provision requires 4 years of
implementation leadtime following the promulgation of new or revised
standards, and that these standards had not been promulgated in a final
rule in time to satisfy this leadtime provision. We are still in the
process of finalizing this rule and so at this time we are not able to
announce the outcome of the leadtime issue. However, we do expect that,
should the gasoline engine and vehicle standards be delayed to model
year 2005, the standards being proposed today for gasoline engines and
vehicles would first apply in model year 2008, rather than 2007, due to
another part of the Clean Air Act section 202(a)(3)(C) provision that
requires 3 model years of stability between changed standards. We
invite comment on the appropriateness of this expectation and on any
issues that might arise in connection with the model year 2008
implementation schedule.

E. Feasibility of the Proposed New Standards

For more detail on the arguments supporting our assessment of the
technological feasibility of today's proposed standards, please refer
to the Draft RIA in the docket for this rule. The following discussion
summarizes the more detailed discussion found in the Draft RIA.
1. Feasibility of Stringent Standards for Heavy-Duty Diesel
Diesel engines have made great progress in lowering engine-out
emissions from 6.0 g/bhp-hr NO_X and 0.6 g/bhp-hr PM in 1990
to 4.0 g/bhp-hr NO_X and 0.1 g/bhp-hr PM in 1999. These
reductions came initially with improvements to combustion and fuel
systems. Introduction of electronic fuel systems in the early 1990s
allowed lower NO_X and PM levels without sacrificing fuel
economy. This, combined with increasing fuel injection pressures, has
been the primary technology that has allowed emission levels to be
reduced to current 1999 levels. Further engine-out NO_X
reductions to the levels necessary to comply with the 2004 standard of
2.5 g/bhp-hr NO_X+NMHC will come primarily from the
addition of cooled EGR.
Engine out emission reductions beyond the 2.5 g/bhp-hr level are
expected with low sulfur fuel and more experience with cooled EGR
systems. Low sulfur fuel will allow more EGR to be used at lower
temperatures because of the reduced threat of sulfuric acid formation.
In addition, recirculating the exhaust gases from downstream of a PM
trap may allow different EGR pumping configurations to be feasible.
Such pumping configurations could provide a better NO_X/fuel
consumption tradeoff.
These potential engine-out emission reductions are expected to be
modest and are not expected to be sufficient to meet the emission
standards proposed

[[Page 35467]]

today. However, they would allow greater flexibility in choosing the
combination of technologies used to meet the proposed emission
standards. With lower engine-out emissions, it might be most cost
effective to use smaller and less expensive exhaust emission control
devices, for instance. Also, the combination of engine-out and exhaust
emission control could be chosen for the best fuel economy. The fuel
economy trade-offs between lower engine-out emissions and more
effective exhaust emission control might be such that a combination of
the two methods provide fuel economy that is better than either method
on its own. As a result, additional engine-out emission reductions are
expected to add additional flexibility in combination with exhaust
emission control in jointly optimizing costs, fuel economy, and
emissions.

a. Meeting the Proposed PM Standard

Diesel PM consists of three primary constituents: unburned carbon
particles, which make up the largest portion of the total PM; the
soluble organic fraction (SOF), which consists of unburned hydrocarbons
that have condensed into liquid droplets or have condensed onto
unburned carbon particles; and sulfates, which result from oxidation of
fuel borne sulfur in the engine's exhaust.
Several exhaust emission control devices have been developed to
control harmful diesel PM constituents--the diesel oxidation catalyst
(DOC), and the many forms of particulate filters, or traps. DOCs have
been shown to be durable in use, but they effectively control only the
SOF portion of the total PM which, especially on today's engines,
constitutes only around 10 to 30 percent of the total PM. Therefore,
the DOC does not address our PM concerns sufficiently.
At this time, only the PM trap is capable of providing the level of
control sought by today's proposed PM standards. In the past, the PM
trap has demonstrated highly efficient trapping efficiency, but
regeneration of the collected PM has been a serious challenge. The PM
trap works by passing the exhaust through a ceramic or metallic filter
to collect the PM. The collected PM, mostly carbon particles but also
the SOF portion, must then be burned off the filter before the filter
becomes plugged. This burning off of collected PM is referred to as
``regeneration,'' and can occur either:
on a periodic basis by using base metal catalysts or an
active regeneration system such as an electrical heater, a fuel burner,
or a microwave heater; or,
on a continuous basis by using precious metal catalysts.
Uncatalyzed diesel particulate traps demonstrated high PM trapping
efficiencies many years ago, but the level of the PM standard was such
that it could be met through less costly ``in-cylinder'' control
techniques. Also, the regeneration characteristics were not dependable.
As a result, some systems employed electrical heaters or fuel burners
to improve upon regeneration, but these complicated the system design
and still could not provide the durability and dependability required
for HD diesel applications.
We believe the most desirable PM trap, and the type of trap that
will prove to be the industry's technology of choice, is one capable of
regenerating on an essentially continuous basis. We also believe that
such traps are the most promising for enabling very low PM emissions
because:
They are highly efficient at trapping all forms of diesel
PM;
They employ precious metals to reduce the temperature at
which regeneration occurs, thereby allowing for passive regeneration
under normal operating conditions typical of a diesel engine;\81\
---------------------------------------------------------------------------

\81\ For PM trap regeneration without precious metals,
temperatures in excess of 650 deg.C must be obtained. At such high
temperatures, carbon will burn provided sufficient oxygen is
present. However, although the largest heavy-duty diesels may
achieve temperatures of 650 deg.C under some operating conditions,
smaller diesel engines, particularly light-duty and light heavy-duty
diesel engines, will rarely achieve such high temperatures. For
example, exhaust temperatures on the HDE Federal Test Procedure
cycle typically range from 100 deg.C to 450 deg.C. Precious metal
catalyzed traps use platinum to oxidize NO in the exhaust to
NO2, which is capable of oxidizing carbon at temperatures
as low as 250 deg.C to 300 deg.C.
---------------------------------------------------------------------------

Because they regenerate continuously, they have lower
average backpressure thereby reducing potential fuel economy impacts;
and,
Because of their passive regeneration characteristics,
they need no extra burners or heaters like would be required by an
active regeneration system thereby reducing potential fuel economy
impacts.
These catalyzed PM traps are able to provide in excess of 90
percent control of diesel PM. However, as discussed in detail in the
Draft RIA, the catalyzed PM trap cannot regenerate properly with
current fuel sulfur levels as such sulfur levels inhibit the NO to
NO2 reaction to the point of stopping trap regeneration.\82\
Also, because SO2 is so readily oxidized to SO3,
very low PM standards cannot be achieved with current sulfur levels
because of the resultant increase in sulfate PM emissions.\83\
---------------------------------------------------------------------------

\82\ Cooper and Thoss, Johnson Matthey, SAE 890404.
\83\ See the Draft RIA for more detail on the relationship of
fuel sulfur to sulfate make.
---------------------------------------------------------------------------

More than one exhaust emission control manufacturer is known to be
developing these precious metal catalyzed, passively regenerating PM
traps and to have them in broad field test programs in areas where low
sulfur diesel fuel is currently available. In field trials, they have
demonstrated highly efficient PM control and promising durability with
some units accumulating in excess of 360,000 miles of field use.\84\
The experience gained in these field tests also helps to clarify the
need for very low sulfur diesel fuel. In Sweden and some European city
centers where below 10 ppm diesel fuel sulfur is readily available,
more than 3,000 catalyzed diesel particulate filters have been
introduced into retrofit applications without a single failure. The
field experience in areas where sulfur is capped at 50 ppm has been
less definitive. In regions without extended periods of cold ambient
conditions, such as the United Kingdom, field tests on 50 ppm cap low
sulfur fuel have been extremely positive, matching the success at, 10
ppm. However, field tests in Finland where colder winter conditions are
sometimes encountered (similar to northern parts of the United States)
have revealed a failure rate of 10 percent. This 10 percent failure
rate has been attributed to insufficient trap regeneration due to fuel
sulfur in combination with low ambient temperatures.\85\ As the ambient
conditions in Sweden are expected to be no less harsh than Finland, we
are left to conclude that the increased failure rates noted here are
due to the higher fuel sulfur level in a 50 ppm cap fuel versus a 10
ppm cap fuel. From these results, we can also theorize that lighter
applications (such as large pick-up trucks and other light heavy-duty
applications), having lower exhaust temperatures than heavier
applications, may experience similar results and would, therefore, need
very low sulfur fuel. These results are understood to be due to the
effect of sulfur on the trap's ability to create sufficient
NO2 to carry out proper trap regeneration. Without the
NO2, the trap continues to trap at high efficiency, but it
is unable to oxidize, or regenerate, the trapped PM. The possible
result is a plugged trap.
---------------------------------------------------------------------------

\84\ Allansson, et at., SAE 2000-01-0480.
\85\ Letter from Dr. Barry Cooper to Don Lopinski US EPA, EPA
Docket A-99-06.
---------------------------------------------------------------------------

Diesel particulate traps reduce particulate matter (PM) by
capturing and burning particles. Ninety percent of

[[Page 35468]]

the PM mass resides in particle sizes that are less than 1000
nanometers (nm) in diameter, and half of these particles are less than
200 nm. Fortunately, PM traps have very high particle capture
efficiencies. PM less than 200 nm is captured efficiently by diffusion
onto surfaces within the trap walls. Larger particles are captured
primarily by inertial impaction onto surfaces due to the tortuous path
that exhaust gas must take to pass through the porous trap walls.
Capture efficiency for elemental carbon (soot) and metallic ash is
nearly 100 percent; therefore, significant PM can only form downstream
of the trap. Volatile PM forms from sulfate or organic vapors via
nucleation, condensation, and/or adsorption during initial dilution of
raw exhaust into the atmosphere. Kleeman,\86\ et. al., and
Kittelson,\87\ et. al., independently demonstrated that these volatile
particles reside in the ultra-fine PM range (i.e. 100 nm range).
---------------------------------------------------------------------------

\86\ Kleeman, M.J., Schauer, J.J., Cass, G.R., 2000, Size and
Composition Distribution of Fine Particulate Matter Emitted From
Motor Vehicles, Environmental Science and Technology, Vol. 34, No.
7.
\87\ Kittelson, D.B., 2000, Presentation on Fuel and Lube Oil
Sulfer and Oxidizing Aftertreatment System Effects on Nano-particle
Emissions from Diesel Engines. Presented in United Kingdom April 12,
2000.
---------------------------------------------------------------------------

Modern catalyzed PM traps have been shown to be very effective at
reducing PM mass. In addition, they can significantly reduce the
overall number of emitted particles when operated on low sulfur fuel.
Hawker, et al., found that a modern catalyzed PM trap reduced particle
count by over 95 percent, including ultrafine particles ( 50 nm) at
most of the tested conditions. The lowest observed efficiency in
reducing particle number was 86 percent. No generation of particles by
the PM trap was observed under any tested conditions.\88\ Kittelson, et
al., confirmed that ultrafine particles can be reduced by a factor of
ten by oxidizing volatile organics, and by an additional factor of ten
by reducing sulfur in the fuel. Catalyzed PM traps efficiently oxidize
nearly all of the volatile organic PM precursors, and elimination of as
much fuel sulfur as possible will dramatically reduce the number of
ultrafine PM emitted from diesel engines. Therefore, the combination of
PM traps with low sulfur fuel is expected to result in a very large
reduction in PM mass, and ultrafine particles will be almost completely
eliminated.
---------------------------------------------------------------------------

\88\ Hawker, P., et al., Effect of a Continuously Regenerating
Diesel Particulate Filter on Non-Regulated Emissions and Particle
Size Distribution, SAE 980189.
---------------------------------------------------------------------------

Now that greater than 90 percent effective PM emission control has
been demonstrated, focus has turned to bringing PM exhaust emission
control to market. One of the drivers is the Euro IV PM standard set to
become effective in 2005.\89\ This standard sets a PM trap forcing
emission target. In anticipation of the 2005 introduction date, field
tests are already underway in several countries with catalyzed
particulate filters. We believe the experience gained in Europe with
these technologies will coincide well with the emission standards in
this proposal. The timing of today's proposal harmonizes the heavy-duty
highway PM technologies with those expected to be used to meet the
light-duty highway Tier 2 standards. Our own testing with fuel sulfur
levels below 10 ppm shows that these systems are viable.\90\ With this
level of effort already under way, we believe that the proposed PM
standards which would require a 90 percent reduction in the mass of
particulate emissions could be met provided low sulfur fuel is made
available.
---------------------------------------------------------------------------

\89\ The Euro IV standards are 2.6 g/hp-hr NO_X and
0.015 g/hp-hr PM.
\90\ Memorandum from Charles Schenk, EPA, to Air Docket A-99-06,
``Summary of EPA PM Efficiency Data,'' May 8, 2000.
---------------------------------------------------------------------------

The data currently available show that catalyzed particulate
filters can provide significant reductions in PM. Catalyzed particulate
filters, in conjunction with low sulfur fuel, have been shown to be
more than 90 percent efficient over the FTP and at most supplemental
steady-state modes.\91\ However, with the application of exhaust
emission control technology and depending on the sulfur level of the
fuel, there is the potential for sulfate production during some
operating modes covered by the NTE and the supplemental steady-state
test. We believe that, with the 15 ppm diesel sulfur level proposed
today, the NTE and the supplemental steady-state test, as proposed in
the 2004 heavy-duty rule, would be feasible. This belief, as discussed
in greater detail in the draft RIA, is supported by data generated as
part of the Diesel Emission Control Sulfur Effects (DECSE) test
program.\92\ We request comment and relevant data on this issue.
---------------------------------------------------------------------------

\91\ Demonstration of Advanced Emission Control Technologies
Enabling Diesel-Powered Heavy-Duty Engines to Achieve Low Emission
Levels, Manufacturers of Emissions Controls Association, June 1999.
\92\ Diesel Emission Control Sulfur Effects (DECSE) Program--
Phase II Interim Data Report No. 4, Diesel Particulate Filters--
Final Report, January 2000, Table C1, www.ott.doe.gov/decse.
---------------------------------------------------------------------------

We request comment on the potential need to remove, clean, and
reverse these traps at regular intervals to remove ash build-up
resulting from engine oil. Small amounts of oil can enter the exhaust
via the combustion chamber (past the pistons, rings and valve seals),
and via the crankcase ventilation system. This can lead to ash build-
up, primarily as a result of the metallic oil additives used to provide
pH control. Such pH control is necessary, in part, to neutralize
sulfuric acid produced as a byproduct of burning fuel containing
sulfur. However, with reduced fuel sulfur, these oil additives could be
reduced, thereby reducing the rate of ash build-up and lengthening any
potential cleaning intervals. It may also be possible to use oil
additives that are less prone to ash formation to reduce the need for
periodic maintenance. We believe that catalyzed PM traps should be able
to meet the required emissions reduction goals over their useful life
with minimal maintenance. Nonetheless, we request comment on the
appropriate minimum allowable maintenance interval for PM traps.
Commenters should consider whether the maintenance interval should
include design provisions to ensure quick and easy maintenance and
should make suggestions for how performance of the maintenance by the
owner would be ensured.

b. Meeting the Proposed NO_X Standard

The NO_X standard proposed today requires approximately a
90 percent reduction in NO_X emissions beyond the levels
expected from the 2004 emission standards. Historically, catalytic
reduction of NO_X emissions in the oxygen-rich environment
typical of diesel exhaust has been difficult because known
NO_X reduction mechanisms tend to be highly selective for
oxygen rather than NO_X. Nonetheless, there are exhaust
emission control devices that reduce the NO_X to form
harmless oxygen and nitrogen. These devices are the lean NO_X
catalyst, the NO_X adsorber, selective catalytic reduction
(SCR), and non-thermal plasma.
The lean NO_X catalyst has been shown to provide up to a
30 percent NO_X reduction under limited steady-state
conditions. Despite a large amount of development effort,
NO_X reductions over the heavy-duty transient federal test
procedure (FTP) have been demonstrated only on the order of 12
percent.\93\ Consequently, the lean NO_X

[[Page 35469]]

catalyst does not appear to be capable of enabling the significantly
lower NO_X emissions required by the proposed NO_X
standard.
---------------------------------------------------------------------------

\93\ Kawanami, M., et al., Advanced Catalyst Studies of Diesel
NO_X Reduction for On-Highway Trucks, SAE 950154.
---------------------------------------------------------------------------

NO_X adsorbers were first introduced in the power
generation market less than five years ago. Since then, NO_X
adsorber systems in stationary source applications have enjoyed
considerable success. In 1997, the South Coast Air Quality Management
District of California determined that a NO_X adsorber system
provided the ``Best Available Control Technology'' NO_X limit
for gas turbine power systems.\94\ Average NO_X control for
these power generation facilities is in excess of 92 percent.\95\
---------------------------------------------------------------------------

\94\ Letter from Barry Wallerstein, Acting Executive Officer,
SCAQMD, to Rober Danziger, Goal Line Environmental Technologies,
dated December 8, 1997, www.glet.com.
\95\ Reyes and Cutshaw, SCONO_X Catalytic Absorption
System, December 8, 1998. www.glet.com.
---------------------------------------------------------------------------

Recently, the NO_X adsorber's stationary source success
has caused some to turn their attention to applying NO_X
adsorber technology to lean burn engines in mobile source applications.
With only a few years of development effort, NO_X adsorber
catalysts have been developed and are now in production for gasoline
direct injection vehicles in Japan. The 2000 model year will see the
first U.S. application of this technology with the introduction of the
Honda Insight, which will be certified to the California LEV-I ULEV
category standard.
Although diesel vehicle manufacturers have not yet announced
production plans for NO_X adsorber-based systems, they are
known to have development efforts underway to demonstrate their
potential. In Europe, both Daimler-Chrysler and Volkswagen, driven by a
need to meet stringent Euro IV emission standards, have published
results showing how they would apply the NO_X adsorber
technology to their diesel powered passenger cars. Volkswagen reports
that it has already demonstrated NO_X emissions of 0.137
g/km (0.22 g/mi) on a diesel powered Passat passenger car equipped with
a NO_X adsorber catalyst.\96\
---------------------------------------------------------------------------

\96\ Pott, E., et al., Potential of NO_X-Trap Catalyst
Application for DI-Diesel Engines.
---------------------------------------------------------------------------

Likewise, in the United States, heavy-duty engine manufacturers
have begun investigating the use of NO_X adsorber
technologies as a more cost effective means to control NO_X
emissions when compared to more traditional in-cylinder approaches.
Cummins Engine Company reported, at DOE's 1999 Diesel Engine Emissions
Reduction workshop, that they had demonstrated an 80 percent reduction
in NO_X emissions over the Supplemental Steady State test and
58 percent over the heavy-duty FTP cycle using a NO_X
adsorber catalyst.
In spite of these promising developments, work in the United States
on NO_X adsorbers has been limited in comparison to the rest
of the world for at least a couple of reasons: (1) prior to today's
proposal, emission standards have not necessitated the use of
NO_X exhaust emission controls on heavy-duty diesel engines;
and, (2) there has not been a commitment in the U.S. to guarantee the
availability of low sulfur diesel fuel. This is in stark contrast to
Europe where the Euro IV and Euro V emission standards, along with the
commitment to low sulfur diesel fuel, have led to rapid advancements of
NO_X exhaust emission control technology. We believe, based
on input from industry members that develop and manufacture emission
control devices such as NO_X adsorbers, that the prospect of
low sulfur diesel fuel in the U.S. market will drive rapid advancement
of this promising NO_X control technology.\97\
---------------------------------------------------------------------------

\97\ Letter from Bruce Bertelsen, Executive Director,
Manufacturers of Emission Controls Association, to Margo Oge, EPA,
dated April 5, 2000.
---------------------------------------------------------------------------

NO_X adsorbers work by providing a NO_X storage
feature, a NO_X adsorber, during periods of fuel lean
operation. This is then combined with the typical three-way catalyst,
like those used for years in stoichiometric gasoline applications. The
combination of adsorber plus three-way catalyst allows storage of
NO_X on the adsorber during fuel lean-oxygen rich operation,
then removal of NO_X from the adsorber and reduction of
NO_X over the three-way catalyst during fuel rich-oxygen lean
operation. This removal of NO_X from the adsorber is termed
``NO_X regeneration'' and generally requires purposeful
controlled addition of small amounts of fuel into the exhaust stream at
regular intervals.
Improving NO_X reduction efficiencies over the diesel
exhaust temperature range is key to meeting the proposed standards.
Current NO_X adsorbers, for instance, have a high reduction
efficiency (over 90 percent NO_X reduction) over a fairly
broad temperature range (exhaust temperatures from 250 deg.C to
450 deg.C) allowing today's proposed standard to be met over this
range.\98\ Extending the range of high NO_X reduction
efficiency at both high temperatures and low temperatures will allow
higher average reduction efficiencies over the FTP and in use. The
performance of the NO_X adsorber may vary somewhat with
exhaust temperature across the NTE. For that reason, engine-out
NO_X emissions will have to be flattened over the NTE to
accommodate these variations in NO_X reduction performance.
We believe that such an approach would allow the NO_X NTE and
supplemental steady-state composite to be met. We seek comment and data
on the relationship between NO_X adsorber performance and
engine operating mode.
---------------------------------------------------------------------------

\98\ Dou, D., Bailey, O., Investigation of NO_X
Adsorber Catalyst Deactivation, SAE 982594.
---------------------------------------------------------------------------

The greatest hurdle to the application of the NO_X
adsorber technology has been its sensitivity to sulfur in diesel fuel.
The NO_X adsorber stores sulfur emissions in a manner
directly analogous to its storage of NO_X under lean
conditions. Unfortunately, the stored sulfur is not readily removed
from the adsorber during the type of operating conditions under which
NO_X is readily removed. This leads to an eventual loss of
NO_X adsorber function and, thus, a loss of NO_X
emission control. This potential loss of NO_X adsorber
function can most effectively be addressed through the reduction of
sulfur in diesel fuel. For a more complete description of the
sensitivity of this technology to sulfur in diesel fuel, and for an
explanation of the need for low sulfur diesel fuel, please refer to
section III.F.
The preceding discussion of NO_X adsorbers assumes that
SO_X (SO2 and SO3) emissions will be
``trapped'' on the surface of the catalyst effectively poisoning the
device and requiring a ``desulfation'' (sulfur removal event) to
recover catalyst efficiency. We believe that, at the proposed 15 ppm
cap fuel sulfur level, this strategy will allow effective
NO_X control with moderately frequent desulfation and with a
modest fuel consumption of one percent, which we anticipate will be
more that offset by reduced reliance on current more expensive (from a
fuel economy standpoint) NO_X control strategies (see
discussion in section III.F for estimates of overall fuel economy
impacts). In order to reduce the fuel economy impact and to simplify
engine control, some manufacturers are investigating the use of
SO_X ``traps'' (sometimes called SO_X
``adsorbers'') to remove sulfur from the exhaust stream prior to it
flowing through the NO_X adsorber catalyst.
The SO_X trap is, in essence, a modified NO_X
adsorber designed to preferentially store (trap) sulfur on its surface
rather than NO_X. It differs from a NO_X adsorber
in that it is not effective at storing NO_X and it more
easily releases stored sulfur. A SO_X trap placed upstream of
a NO_X adsorber could effectively remove very modest

[[Page 35470]]

amounts of sulfur from the exhaust, thereby limiting sulfur's effect on
the NO_X adsorber. Unfortunately, the SO_X trap
like the NO_X adsorber, will eventually fill every available
storage site with sulfate and will cease to function unless the sulfur
is removed. Desulfating the SO_X adsorber on the vehicle is
problematic since it would be upstream of the NO_X adsorber
which could then be poisoned quite rapidly by the SO_X
released from the SO_X trap. This problem could presumably be
solved through some form of NO_X adsorber by-pass during
SO_X trap desulfation (although control of NO_X
during this event may be problematic). Alternatively, removal and
replacement of the SO_X adsorber on a fixed service interval
would solve this problem, albeit at some cost. In an oral presentation
made to EPA, an engine manufacturer estimated the storage capacity of a
SO_X trap at approximately one pound of SO2 per
cubic foot of catalyst.\99\ For fuel with a seven ppm average sulfur
level, this would mean replacement of a 48 liter SO_X trap
approximately every 100,000 miles.\100\ This more than doubles the
catalyst size we have projected for a typical heavy heavy-duty vehicle
in this proposal, while only providing protection for a small fraction
of its useful life. Because of practical limitations on SO_X
trap size, we do not believe that the use of SO_X traps can
avoid the need for very low-sulfur diesel fuel, and we have received no
information from manufacturers that contradicts this belief. We invite
comment on the use of a SO_X trap to protect NO_X
adsorbers and on the appropriateness of SO_X traps being
replaced on a fixed interval as described here. Further, we request
comment and supporting data to indicate the interval at which
SO_X traps would require replacement.
---------------------------------------------------------------------------

\99\ Memorandum from Byron Bunker, US EPA to Air Docket A-99-06,
``Meeting between EPA, OMB, representatives of major oil companies,
and representatives of major diesel engine manufacturers,'' Item II-
E-17.
\100\ This estimate assumes that a heavy-duty vehicle averages
six miles per gallon of fuel, that diesel fuel weighs seven pounds
per gallon, that diesel fuel has seven ppm sulfur, and that a sulfur
trap could store one pound of SO2 in a cubic foot of
catalyst.
---------------------------------------------------------------------------

Selective Catalytic Reduction (SCR), like NO_X adsorber
technology, was first developed for stationary applications and is
currently being refined for the transient operation found in mobile
applications.\101\ With the SCR system, a urea solution is injected
upstream of the catalyst which breaks down the urea into ammonia and
carbon dioxide. Catalysts containing precious metals (platinum) can be
used at the inlet and outlet of SCR systems designed for mobile
applications to improve low temperature NO_X reduction
performance and to oxidize any ammonia that may pass through the SCR,
respectively. Such SCR systems are referred to as ``Compact SCR.'' The
use of these platinum catalysts enable Compact SCR systems to achieve
large NO_X reductions, but introduce sensitivity to sulfur in
much the same way as for diesel particulate filter technologies. Sulfur
in diesel fuel inhibits low temperature performance and results in high
sulfate make leading directly to higher particulate emissions. For a
further discussion of Compact SCR system sensitivity to sulfur in
diesel fuel, and of its need for low sulfur diesel fuel, refer to
section III.F.
---------------------------------------------------------------------------

\101\ SRC systems being developed for mobile applications are
more appropriately called ``compact SCR'' systems, which incorporate
on oxidation catalyst. Generally, reference to SCR throughout this
preamble should be taken to mean compact SCR.
---------------------------------------------------------------------------

The reduction efficiency window for Compact SCR is similar to the
NO_X adsorber, with greater than 80 percent efficiency at
exhaust temperatures as low as 250 deg.C.\102\ Peak efficiency values
of over 90 percent are possible under certain conditions, but the cool
exhaust temperature characteristics of diesel engines make excursions
outside the optimum efficiency window of current Compact SCR systems
quite frequent. As a result, the cycle average NO_X reduction
efficiency is on the order of 77 percent over the heavy-duty FTP.\103\
Over the Supplemental Steady State test modes, the SCR has been shown
to have 65-99 percent efficiency.\104\ The high efficiency over a broad
temperature range should also allow the NTE to be met. With additional
development effort, we believe the NO_X reduction efficiency
of SCR can be further improved to meet NO_X levels as low as
those proposed today.
---------------------------------------------------------------------------

\102\ Klein, H., et al., NO_X Reduction for Diesel
Vehicles, Degussa-Huls AG, Corning Clean Diesel Workshop, Sept. 27-
29, 1999.
\103\ ``Demonstration of Advanced Emission Control Technologies
Enabling Diesel-Powered Heavy-Duty Engines to Achieve Low Emission
Levels,'' Manufacturers of Emission Controls Association, June 1999.
\104\ ``Demonstration of Advanced Emission Control Technologies
Enabling Diesel-Powered Heavy-Duty Engines to Achieve Low Emission
Levels,'' Manufacturers of Emission Controls Association, June 1999.
---------------------------------------------------------------------------

However, significant challenges remain for Compact SCR systems to
be applied to mobile source applications. In addition to the need for
very low sulfur diesel fuel to achieve high NO_X conversion
efficiencies and to control sulfate PM emissions, Compact SCR systems
require vehicles to be refueled with urea. The infrastructure for
delivering urea at the pump needs to be in place for these devices to
be feasible in the marketplace; and before development of the
infrastructure can begin, the industry must decide upon a standardized
method of delivery for the urea supply. In addition to this, there
would need to be adequate safeguards in place to ensure the urea is
used throughout the life of the vehicle, since, given the added cost of
urea, there would be incentive not to refill the urea tank. Because
urea is required for the SCR system to function, urea replenishment
would need to be assured.
Another, very recent approach to NO_X reduction is the
non-thermal plasma assisted catalyst. This system works by applying a
high voltage across two metal plates in the exhaust stream to form ions
that serve as oxidizers. Essentially, the plasma would displace a
conventional platinum based oxidation catalyst in function. Once
oxidized to NO2, NO_X can be more readily reduced
over a precious metal catalyst. While the concept is promising, this
technology is so new that essentially no data exists showing its
effectiveness at controlling NO_X. We expect that, if and
when the non-thermal plasma approach to NO_X control becomes
viable, it will also require the use of low sulfur diesel fuel due to
its reliance on a precious metal catalyst to reduce the
NO2.\105\
---------------------------------------------------------------------------

\105\ ``The Impact of Sulfur in Diesel Fuel on Catalyst Emission
Control Technology,'' report by the Manufacturers of Emission
Controls Association, March 15, 1999.
---------------------------------------------------------------------------

Based on the discussion above, we believe that NO_X
aftertreatment technology, in combination with low sulfur diesel fuel,
is capable of meeting the very stringent NO_X standards we
have proposed. The clear intent that this proposal provides to make
very low sulfur diesel fuel available in the future and to establish
emission standards which necessitate advanced NO_X controls
should enable rapid development of these technologies. The
NO_X adsorber technology has shown incredible advancement in
the last five years, moving from stationary source applications to
lean-burn gasoline, and now to heavy-duty diesel engines. Given this
rapid progress, the availability of very low sulfur diesel fuel, and
the lead time provided by today's proposal, we believe that applying
NO_X adsorbers to heavy-duty diesel engines would enable
manufacturers to comply with our proposed standards. Compact SCR has
been slower in developing than NO_X adsorbers but could be
applied to mobile source applications if the

[[Page 35471]]

difficult urea infrastructure issues can be addressed.

c. Meeting the Proposed NMHC Standard

Meeting the NMHC standards proposed today should not present any
special challenges to diesel manufacturers. Since all of the devices
discussed above--catalyzed particulate filters, NO_X
adsorbers, and SCR--contain platinum and other precious metals to
oxidize NO to NO2, they are also very efficient oxidizers of
hydrocarbons. Reductions of greater than 95 percent have been shown
over transient FTP and supplemental steady-state modes.\106\ Given that
typical engine-out NMHC is expected to be in the 0.2 g/bhp-hr range for
engines meeting the 2004 standards, this level of NMHC reduction will
easily allow the 0.14 g/bhp-hr NMHC standard to be met over the
transient FTP, the supplemental steady-state test, and the NTE zone.
---------------------------------------------------------------------------

\106\ ``The Impact of Sulfur in Diesel Fuel on Catalyst Emission
Control Technology,'' report by the Manufacturers of Emission
Controls Association, March 15, 1999, pp. 9 & 11.
---------------------------------------------------------------------------

d. Meeting the Crankcase Emissions Requirements

The most common way to eliminate crankcase emissions has been to
vent the blow-by gases into the engine air intake system, so that the
gases can be recombusted. Until today's proposal, we have required that
crankcase emissions be controlled only on naturally aspirated diesel
engines. We have made an exception for turbocharged heavy-duty diesel
engines because of concerns in the past about fouling that could occur
by routing the diesel particulates (including engine oil) into the
turbocharger and aftercooler. However, this is an environmentally
significant exception since most heavy-duty diesel trucks use
turbocharged engines, and a single engine can emit over 100 pounds of
NO_X, NMHC, and PM from the crankcase over the lifetime of
the engine.
Therefore, we have proposed to eliminate this exception. We
anticipate that the heavy-duty diesel engine manufacturers will be able
to control crankcase emissions through the use of closed crankcase
filtration systems or by routing unfiltered blow-by gases directly into
the exhaust system upstream of the emission control equipment. The
closed crankcase filtration systems work by separating oil and
particulate matter from the blow-by gases through single or dual stage
filtration approaches, routing the blow-by gases into the engine's
intake manifold and returning the filtered oil to the oil sump. These
systems are required for new heavy-duty diesel vehicles in Europe
starting this year. Oil separation efficiencies in excess of 90 percent
have been demonstrated with production ready prototypes of two stage
filtration systems.\107\ By eliminating 90 percent of the oil that
would normally be vented to the atmosphere, the system works to reduce
oil consumption and to eliminate concerns over fouling of the intake
system when the gases are routed through the turbocharger. An
alternative approach would be to route the blow-by gases into the
exhaust system upstream of the catalyzed diesel particulate filter
which would be expected to effectively trap and oxidize the engine oil
and diesel PM. This approach may require the use of low sulfur engine
oil to ensure that oil carried in the blow-by gases does not compromise
the performance of the sulfur sensitive emission control equipment. We
request comment on the use of either approach to crankcase emissions
control.
---------------------------------------------------------------------------

\107\ Letter from Marty Barris Donaldson Corporation to Byron
Bunker US EPA, March 2000. EPA Air Docket A-99-06.
---------------------------------------------------------------------------

e. The Complete System

We expect that the technologies described above would be integrated
into a complete emission control system. The engine-out emissions will
be traded off against the exhaust emission control package in such a
way that the result is the most beneficial from a cost, fuel economy
and emissions standpoint. The engine-out characteristics will also have
to be tailored to the needs of the exhaust emission control devices
used. The NO_X adsorber, for instance, will require periods
of oxygen depleted exhaust flow in order to regenerate. This may be
most efficiently done by reducing the air-fuel ratio that the engine is
operating under during the regeneration to reduce the oxygen content of
the exhaust. Further, it is envisioned that the PM device will be
integrated into the exhaust system upstream of the NO_X
reduction device. This placement would allow the PM trap to take
advantage of the engine-out NO_X as an oxidant for the
particulate, while removing the particulate so that the NO_X
exhaust emission control device will not have to deal with large PM
deposits which may cause a deterioration in performance. Of course,
there is also the possibility of integrating the PM and NO_X
exhaust emission control devices into a single unit to replace a
muffler and save space. Particulate free exhaust may also allow for new
options in EGR system design to optimize its efficiency.
We expect that the exhaust emission control emission reduction
efficiency will vary with temperature and space velocity \108\ across
the NTE zone. Consequently, to maintain the NTE emission cap, the
engine-out emissions would have to be calibrated with exhaust emission
control performance characteristics in mind. This would be accomplished
by lowering engine-out emissions where the exhaust emission control was
less efficient. Conversely, where the exhaust emission control is very
efficient at reducing emissions, the engine-out emissions could be
tuned for higher emissions and better fuel economy. These trade-offs
between engine-out emissions and exhaust emission control performance
characteristics are similar to those of gasoline engines with three-way
catalysts in today's light-duty vehicles. Managing and optimizing these
trade-offs will be crucial to effective implementation of exhaust
emission control devices on diesel applications.
---------------------------------------------------------------------------

\108\ The term, ``space velocity,'' is a measure of the volume
of exhaust gas that flows through a device.
---------------------------------------------------------------------------

2. Feasibility of Stringent Standards for Heavy-Duty Gasoline
Gasoline emission control technology has evolved rapidly in recent
years. Emission standards applicable to 1990 model year vehicles
required roughly 90 percent reductions in exhaust NMHC and CO emissions
and a 75 percent reduction in NO_X emissions compared to
uncontrolled emissions. Today, some vehicles' emissions are well below
those necessary to meet the current federal heavy-duty gasoline
standards, the proposed 2004 heavy-duty gasoline standards, and the
California Low-Emission Vehicle standards for medium-duty vehicles. The
continuing emissions reductions have been brought about by ongoing
improvements in engine air-fuel management hardware and software plus
improvements in exhaust system and catalyst designs.
We believe that the types of changes being seen on current vehicles
have not yet reached their technological limits and continuing
improvement will allow them to meet today's proposed standards. The
Draft RIA describes a range of specific emission control techniques
that we believe could be used. There is no need to invent new
technologies, although there will be a need to apply existing
technology more effectively and more broadly. The focus of the effort
will be in the application and optimization of these existing
technologies.

[[Page 35472]]

In our light-duty Tier 2 rule, we have required that gasoline
sulfur levels be reduced to a 30 ppm average, with an 80 ppm maximum.
This sulfur level reduction is the primary enabler for the Tier 2
standards. Similarly, we believe that the gasoline sulfur reduction,
along with refinements in existing gasoline emission control
technology, will be sufficient to allow heavy-duty gasoline vehicles
and engines to meet the emission standards sought by today's proposal.
However, we recognize that the emission standards are stringent,
and considerable effort would have to be undertaken. For example, we
expect that every engine would have to be recalibrated to improve upon
its cold start emission performance. Manufacturers would have to
migrate their light-duty calibration approaches to their heavy-duty
offerings to provide cold start performance in line with what they will
have to achieve to meet the Tier 2 standards.
We also project that the proposed 2007 heavy-duty standards would
require the application of advanced engine and catalyst systems similar
to those projected for their light-duty counterparts. Historically,
manufacturers have introduced technology on light-duty gasoline
applications and then applied those technologies to their heavy-duty
gasoline applications. The proposal would allow manufacturers to take
this same approach for 2007. In other words, we expect that
manufacturers would meet the proposed 2007 standards through the
application of technology developed to meet light-duty Tier 2 standards
for 2004.
Improved calibration and systems management would be critical in
optimizing the performance of the engine with the advanced catalyst
system. Precise air/fuel control must be tailored for emissions
performance and must be optimized for both FTP and SFTP type driving.
Calibration refinements may also be needed for EGR system optimization
and to reduce cold start emissions through methods such as spark timing
retard. We also project that electronic control modules with expanded
capabilities would be needed on some vehicles and engines.
We also expect increased use of other technologies in conjunction
with those described above. We expect some increased use of air
injection to improve upon cold start emissions. We may also see air-gap
manifolds, exhaust pipes, and catalytic converter shells as a means of
improving upon catalyst light-off times thereby reducing cold start
emissions. Other, non-catalyst related improvements to gasoline
emission control technology include, as already stated, higher speed
computer processors which enable more sophisticated engine control
algorithms and improved fuel injectors providing better fuel
atomization thereby improving fuel combustion.
Catalyst system durability is, and will always be, a serious
concern. Historically, catalysts have deteriorated when exposed to very
high temperatures. This has long been a concern especially for heavy-
duty work vehicles. However, catalyst manufacturers continue to make
strides in the area of thermal stability and we expect that
improvements in thermal stability will continue for the next generation
of catalysts.
We believe that, by optimizing all of these technologies,
manufacturers will be able to achieve the proposed emission levels.
Advanced catalyst systems have already shown potential to reduce
emissions to close to the proposed levels. Some current California
vehicles are certified to levels below 0.2 g/mi NO_X.
California tested an advanced catalyst system on a vehicle loaded to a
test weight comparable to a heavy-duty vehicle test weight and achieved
NO_X and NMOG levels of 0.1 g/mi and 0.16 g/mi, respectively.
The California vehicle with the advanced catalyst had not been
optimized as a system to take full advantage of the catalyst's
capabilities.
The ABT program can also be an important tool for manufacturers in
implementing a new standard. The program allows manufacturers to
transition to the more stringent standards by introducing emissions
controls over a longer period of time, as opposed to a single model
year. Manufacturers plan their product introductions well in advance.
With ABT, manufacturers can better manage their product lines so that
the new standards don't interrupt their product introduction plans.
Also, the program allows manufacturers to focus on higher sales volume
vehicles first and use credits for low sales volume vehicles.
We request comment on the feasibility of the proposed standards and
request data that would help us evaluate advanced system durability.
3. Feasibility of the Proposed Evaporative Emission Standards
The proposed evaporative emission standards appear to be feasible
now. Many designs have been certified that already meet these
standards. A review of 1998 model year certification data indicates
that five of eight evaporative system families in the 8,500 to 14,000
pound range comply with the proposed 1.4 g/test standard, while all
evaporative system families in the over 14,000 pound range comply with
the proposed 1.9 g/test standard.
The proposed evaporative emission standards would not require the
development of new materials or, in many cases, even the new
application of existing materials. Low permeability materials and low
loss connections and seals are already used to varying degrees on
current vehicles. Today's proposed standards would likely ensure their
consistent use and discourage manufacturers from switching to cheaper
materials or designs to take advantage of the large safety margins they
have under current standards.
There are two approaches to reducing evaporative emissions for a
given fuel. One is to minimize the potential for permeation and leakage
by reducing the number of hoses, fittings and connections. The second
is to use less permeable hoses and lower loss fittings and connections.
Manufacturers are already employing both approaches.
Most manufacturers are moving to ``returnless'' fuel injection
systems. Through more precise fuel pumping and metering, these systems
eliminate the return line in the fuel injection system. The return line
carries unneeded fuel from the fuel injectors back to the fuel tank.
Because the fuel injectors are in such close contact with the hot
engine, the fuel returned from the injectors to the fuel tank has been
heated. This returned fuel is a significant source of fuel tank heat
and vapor generation. The elimination of the return line also reduces
the total length of hose on the vehicle through which vapors can
permeate, and it reduces the number of fittings and connections through
which fuel can leak.
Low permeability hoses and seals, and low loss fittings are
available and are already used on many vehicles. Fluoropolymer
materials can be added as liners to hose and component materials to
yield large reductions in permeability over such conventional materials
as monowall nylon. In addition, fluoropolymer materials can greatly
reduce the adverse impact of alcohols in gasoline on permeability of
evaporative components, hoses and seals.

F. Need for Low-Sulfur Diesel Fuel

The following discussion will build upon the brief sulfur
sensitivity points made earlier in this section by providing a more in
depth discussion of sulfur's effect on the most promising diesel
exhaust emission control technologies. In order to evaluate the effect
of sulfur

[[Page 35473]]

on diesel exhaust control technologies, we used three key factors to
categorize the impact of sulfur in fuel on emission control function.
These factors were efficiency, reliability, and fuel economy. Taken
together these three factors lead us to believe that diesel fuel sulfur
levels of 15 ppm will be required in order to make feasible the
proposed heavy-duty vehicle emission standards (a discussion of higher
sulfur fuel standards, and what they might mean is included in Section
VI.B). Brief summaries of these factors are provided below. A more in-
depth review is given in the following subsections and the RIA
associated with this proposal.
The efficiency of emission control technologies to reduce harmful
pollutants is directly affected by sulfur in diesel fuel. Initial and
long term conversion efficiencies for NO_X, NMHC, CO and
diesel PM emissions are significantly reduced by catalyst poisoning and
catalyst inhibition due to sulfur. NO_X conversion
efficiencies with the NO_X adsorber technology in particular
are dramatically reduced in a very short time due to sulfur poisoning
of the NO_X storage bed. In addition, total PM control
efficiency is negatively impacted by the formation of sulfate PM. As
explained in detail in the following sections, all of the advanced
NO_X and PM technologies described here have the potential to
make significant amounts of sulfate PM under operating conditions
typical of heavy-duty vehicles. The formation of sulfate PM is likely
to be in excess of the total PM standard proposed today, unless diesel
fuel sulfur levels are at or below 15 ppm. Based on the strong negative
impact of sulfur on emission control efficiencies for all of the
technologies evaluated, we believe that 15 ppm represents an upper
threshold of acceptable diesel fuel sulfur levels.
Reliability refers to the expectation that emission control
technologies must continue to function as required under all operating
conditions for the life of the vehicle. As discussed in the following
sections, sulfur in diesel fuel can prevent proper operation of both
NO_X and PM control technologies. This can lead to permanent
loss in emission control effectiveness and even catastrophic failure of
the systems. Sulfur in diesel fuel impacts reliability by decreasing
catalyst efficiency (poisoning of the catalyst), increasing diesel
particulate filter loading, and negatively impacting system
regeneration functions. Among the most serious reliability concerns
with sulfur levels greater than 15 ppm are those associated with
failure to properly regenerate. In the case of the NO_X
adsorber, failure to regenerate will lead to rapid loss of
NO_X emission control as a result of sulfur poisoning of the
NO_X adsorber bed. In the case of the diesel particulate
filter, sulfur in the fuel reduces the reliability of the regeneration
function. If regeneration does not occur, catastrophic failure of the
filter could occur. It is only by the availability of very low-sulfur
diesel fuels that these technologies become feasible. The analysis
given in the following section makes clear that diesel fuel sulfur
levels will need to be consistent with today's proposed standard in
order to ensure robust operation of the technologies under the variety
of operating conditions anticipated to be experienced in the field.
Fuel economy impacts due to sulfur in diesel fuel affect both
NO_X and PM control technologies. The NO_X adsorber
sulfur regeneration cycle (desulfation cycle) can consume significant
amounts of fuel unless fuel sulfur levels are very low. The larger the
amount of sulfur in diesel fuel, the greater the adverse effect on fuel
economy. As sulfur levels increase above 15 ppm, the adverse effect on
fuel economy becomes more significant, increasing above one percent and
doubling with each doubling of fuel sulfur level. Likewise, PM trap
regeneration is inhibited by sulfur in diesel fuel. This leads to
increased PM loading in the diesel particulate filter and increased
work to pump exhaust across this restriction. With very low sulfur
diesel fuel, diesel particulate filter regeneration can be optimized to
give a lower (on average) exhaust backpressure and thus better fuel
economy. Thus for both NO_X and PM technologies the lower the
fuel sulfur level the better.
1. Diesel Particulate Filters and the Need for Low-Sulfur Fuel
As discussed earlier in this section, un-catalyzed diesel
particulate filters require exhaust temperatures in excess of 650 deg.C
in order for the collected PM to be oxidized by the oxygen available in
diesel exhaust. That temperature threshold for oxidation of PM by
exhaust oxygen can be decreased to 450 deg.C through the use of base
metal catalytic technologies. Unfortunately, for a broad range of
operating conditions diesel exhaust is significantly cooler than
400 deg.C. If oxidation of the trapped PM could be assured to occur at
exhaust temperatures lower than 300 deg.C, then diesel particulate
filters would be expected to be robust for most applications and
operating regimes. The only means that we are aware of to ensure
oxidation of PM (regeneration of the trap) at such low exhaust
temperatures is by using oxidants which are more readily reduced than
oxygen. One such oxidant is NO2.
NO2 can be produced in diesel exhaust through the
oxidation of the nitrogen monoxide (NO), created in the engine
combustion process, across a catalyst. The resulting NO2-
rich exhaust is highly oxidizing in nature and can oxidize trapped
diesel PM at temperatures as cool as 250 deg.C.\109\ Some platinum
group metals are known to be good catalysts to promote the oxidation of
NO to NO2. Therefore in order to ensure passive regeneration
of the diesel particulate filters, significant amounts of platinum
group metals (primarily platinum) are being used in the wash-coat
formulations of advanced diesel particulate filters. The use of
platinum to promote the oxidation of NO to NO2 introduces
several system vulnerabilities affecting both the durability and the
effectiveness of the catalyzed diesel particulate filter when sulfur is
present in diesel exhaust. The two primary mechanisms by which sulfur
in diesel fuel limits the robustness and effectiveness of diesel
particulate filters are inhibition of trap regeneration (i.e.,
inhibition of the oxidation of NO to NO2) and a dramatic
loss in total PM control effectiveness due to the formation of sulfate
PM. Unfortunately, these two mechanisms trade-off against one another
in the design of diesel particulate filters. Changes to improve the
reliability of regeneration by increasing catalyst loadings lead to
increased sulfate emissions and thus loss of PM control effectiveness.
Conversely, changes to improve PM control by reducing the use of
platinum group metals and, therefore, limiting ``sulfate make'' leads
to less reliable regeneration. We believe the only means of achieving
good PM emission control and reliable operation is to reduce sulfur in
diesel fuel to the level proposed today, as shown in the following
subsections.
---------------------------------------------------------------------------

\109\ Hawker, P. et al, Experience with a New Particulate Trap
Technology in Europe, SAE 970182.
---------------------------------------------------------------------------

a. Inhibition of Trap Regeneration Due to Sulfur

The passively regenerating diesel particulate filter technologies
rely on the generation of a very strong oxidant, NO2, to
ensure that the carbon captured by the PM trap's filtering media is
oxidized under normal operating conditions. NO2 is produced
through the oxidation of NO in the exhaust across a platinum catalyst.
This oxidation is inhibited by the presence of

[[Page 35474]]

SO2 in the exhaust stream because the preferential reaction
across the platinum is oxidation of SO2 to SO3,
rather than oxidation of NO to NO2.\110\ This inhibition
limits the total amount of NO2 available for oxidation of
the trapped diesel PM, thereby raising the minimum exhaust temperature
required to ensure trap regeneration. Without sufficient
NO2, the amount of PM trapped in the diesel particulate
filter will continue to increase and can lead to excessive exhaust back
pressure, low engine power, and even catastrophic failure of the diesel
particulate filter itself.
---------------------------------------------------------------------------

\110\ Hawker, P. et al, Experience with a New Particulate Trap
Technology in Europe, SAE 970182.
---------------------------------------------------------------------------

Full field test evaluations and retrofit applications of these
catalytic trap technologies are occurring in parts of Europe where low-
sulfur diesel fuel is already available.\111\ The experience gained in
these field tests helps to clarify the need for very low-sulfur diesel
fuel. In Sweden and some European city centers where below 10 ppm
diesel fuel sulfur is readily available, more than 3,000 catalyzed
diesel particulate filters have been introduced into retrofit
applications without a single failure. Given the large number of
vehicles participating in these test programs and the extended time
periods of operation (some vehicles have been operating with traps for
more than 4 years and in excess of 300,000 miles \112\), this is a
strong indication of the robustness of this technology on 10 ppm low-
sulfur diesel fuel. The field experience in areas where sulfur is
capped at 50 ppm has been less definitive. In regions without extended
periods of cold ambient conditions, such as the United Kingdom, field
tests on 50 ppm cap low-sulfur fuel have also been positive, matching
the success at 10 ppm. However, field tests in Finland where colder
winter conditions are sometimes encountered (similar to many parts of
the United States) have revealed a failure rate of 10 percent. This 10
percent failure rate has been attributed to insufficient trap
regeneration due to fuel sulfur in combination with low ambient
temperatures.\113\ As the ambient conditions in Sweden are expected to
be no less harsh than Finland, we are left to conclude that the
increased failure rates noted here are due to the higher fuel sulfur
level in a 50 ppm cap fuel versus a 10 ppm cap fuel. The failure of
some fraction of the traps to regenerate on 50 ppm cap fuel is believed
to be primarily due to inhibition of the NO to NO2
conversion as described here.
---------------------------------------------------------------------------

\111\ Through tax incentives 50 ppm cap sulfur fuel is widely
available in the United Kingdom and 10 ppm sulfur fuel is available
in Sweden and in certain European city centers.
\112\ Allansson, et al. SAE 2000-01-0480.
\113\ Letter from Dr. Barry Cooper, Johnson Matthey, to Don
Kopinski, US EPA, Air Docket A-99-06.
---------------------------------------------------------------------------

The failure mechanisms experienced by diesel particulate filters
due to low NO2 availability vary significantly in severity
and long term consequences. In the most fundamental sense, the failure
is defined as an inability to oxidize the stored particulate at a rate
fast enough to prevent net particulate accumulation over time. The
excessive accumulation of PM over time blocks the passages through the
filtering media, making it more restrictive to exhaust flow. In order
to continue to force the exhaust through the now more restrictive
filter the exhaust pressure upstream of the filter must increase. This
increase in exhaust pressure is commonly referred to as increasing
``exhaust backpressure'' on the engine.
The increased exhaust backpressure represents increased work being
done by the engine to force the exhaust gas through the increasingly
restrictive particulate filter. Unless the filter is frequently
cleansed of the trapped PM, this increased work can lead to reductions
in engine performance and increases in fuel consumption. This loss in
performance may be noted by the vehicle operator in terms of poor
acceleration and generally poor driveability of the vehicle. In some
cases, engine performance can be so restricted that the engine stalls,
stranding the vehicle. This progressive deterioration of engine
performance as more and more PM is accumulated in the filter media is
often referred to as ``trap plugging.'' Trap plugging also has the
potential to cause engine damage. If the exhaust backpressure gets high
enough to open the exhaust valves prematurely, the exhaust valves can
then strike the piston causing catastrophic engine failure. Whether
trap plugging occurs, and the speed at which it occurs, will be a
function of many variables in addition to the fuel sulfur level; these
variables include the vehicle application, its duty cycle, and ambient
conditions. However, if the fuel sulfur level is sufficient to prevent
trap regeneration in any real world conditions experienced, trap
plugging can occur. This is not to imply that any time a vehicle is
refueled once with high sulfur fuel trap plugging will occur. Rather,
it is important to know that the use of fuel with sulfur levels higher
than 15 ppm significantly increases the chances of particulate filter
failure.
Catastrophic failure of the filter can occur when excessive amounts
of PM are trapped in the filter due to a lack of NO2 for
oxidation. This failure occurs when excessive amounts of trapped PM
begin to oxidize at high temperatures (combustion-like temperatures of
over 1000 deg.C) leading to a ``run-away'' combustion of the PM. This
can cause temperatures in the filter media to increase in excess of
that which can be tolerated by the particulate filter itself. For the
cordierite material commonly used as the trapping media for diesel
particulate filters, the high thermal stresses caused by the high
temperatures can cause the material to crack or melt. This can allow
significant amounts of the diesel particulate to pass through the
filter without being captured during the remainder of the vehicle's
life. That is, the trap is destroyed and PM emission control is lost.
As shown above, sulfur in diesel fuel inhibits NO oxidation leading
to increased exhaust backpressure, reduced fuel economy, compromised
reliability, and potentially engine damage. Therefore, we believe that,
in order to ensure reliable and economical operation over a wide range
of expected operating conditions, diesel fuel sulfur levels should be
at or below 15 ppm. With these very low sulfur levels we believe, as
demonstrated by experience in Europe, that catalyzed diesel particulate
filters will prove to be both durable and effective at controlling
diesel particulate emissions to the very low levels that would be
required by today's proposed standard. We request comment on the
inhibition of trap regeneration due to fuel sulfur, along with
supporting data.

b. Loss of PM Control Effectiveness

In addition to inhibiting the oxidation of NO to NO2,
the sulfur dioxide (SO2) in the exhaust stream is itself
oxidized to sulfur trioxide (SO3) at very high conversion
efficiencies by the precious metals in the catalyzed particulate
filters. The SO3 serves as a precursor to the formation of
hydrated sulfuric acid (H2SO4+H2O), or
sulfate PM, as the exhaust leaves the vehicle tailpipe. Virtually all
of the SO3 is converted to sulfate under dilute exhaust
conditions in the atmosphere as well in the dilution tunnel used in
heavy-duty engine testing. Since virtually all sulfur present in diesel
fuel is converted to SO2, the precursor to SO3,
as part of the combustion process, the total sulfate PM is directly
proportional to the amount of sulfur present in diesel fuel. Therefore,
even though diesel particulate filters are very effective at trapping
the carbon and the SOF portions of the total PM, the

[[Page 35475]]

overall PM reduction efficiency of catalyzed diesel particulate filters
drops off rapidly with increasing sulfur levels due to the production
of sulfate PM.
SO2 oxidation is promoted across a catalyst in a manner
very similar to the oxidation of NO, except it is converted at higher
rates, with peak conversion rates in excess of 50 percent. The
SO2 oxidation rate for a platinum based oxidation catalyst
typical of the type which might be used in conjunction with, or as a
washcoat on, a catalyzed diesel particulate filter can vary
significantly with exhaust temperature. At the low temperatures typical
of some urban driving and the heavy-duty federal test procedure (HD-
FTP), the oxidation rate is relatively low, perhaps no higher than ten
percent. However at the higher temperatures that might be more typical
of non-urban highway driving conditions and the Supplemental Steady
State Test (also called the EURO III or 13 mode test), the oxidation
rate may increase to 50 percent or more. These high levels of sulfate
make across the catalyst are in contrast to the very low SO2
oxidation rate typical of diesel engines (less than 2 percent). This
variation in expected diesel exhaust temperatures means that there will
be a corresponding range of sulfate production expected across a
catalyzed diesel particulate filter.
The U.S. Department of Energy in cooperation with industry
conducted a study entitled Diesel Emission Control Sulfur Effects
(DECSE) to provide insight into the relationship between advanced
emission control technologies and diesel fuel sulfur levels. Interim
report number four of this program gives the total particulate matter
emissions from a heavy-duty diesel engine operated with a diesel
particulate filter on several different fuel sulfur levels. A straight
line fit through this data is presented in Table III.F-1 below showing
the expected total direct PM emissions from a heavy-duty diesel engine
on the supplemental steady state test cycle.\114\
---------------------------------------------------------------------------

\114\ Note that direct emissions are those pollutants emitted
directly from the engine or from the tailpipe depending on the
context in which the term is used, and indirect emissions are those
pollutants formed in the atmosphere through the combination of
direct emissions and atmospheric constituents.

Table III.F-1.--Estimated PM Emissions From a Heavy-Duty Diesel Engine
at the Indicated Average Fuel Sulfur Levels
------------------------------------------------------------------------
Supplemental steady state
-----------------------------
Avg. Fuel Sulfur [ppm] Relative
Tailpipe PM [g/ to 3 ppm
bhp-hr] sulfur
------------------------------------------------------------------------
3......................................... 0.003 ..........
7 *....................................... 0.006 100%
15 *...................................... 0.009 200%
30........................................ 0.017 470%
150....................................... 0.071 2,300%
------------------------------------------------------------------------
* The PM emissions at these sulfur levels are based on a straight-line
fit to the DECSE data; PM emissions at other sulfur levels are actual
DECSE data. (Diesel Emission Control Sulfur Effects (DECSE) Program--
Phase II Interim Data Report No. 4, Diesel Particulate Filters-Final
Report, January 2000, Table C1.) Although DECSE tested diesel
particulate filters at these fuel sulfur levels, they do not conclude
that the technology is feasible at all levels, but they do note that
testing at 150 ppm is a moot point as the emission levels exceed the
engine's baseline emission level.

Table III.F-1 makes it clear that there are significant PM emission
reductions possible with the application of catalyzed diesel
particulate filters and low-sulfur diesel fuel. At the observed sulfate
PM conversion rates, the DECSE program results show that the proposed
total PM standard is feasible for diesel particulate filter equipped
engines operated on fuel with a sulfur level at or below 15 ppm. The
results also show that diesel particulate filter control effectiveness
is rapidly degraded at higher diesel fuel sulfur levels due to the high
sulfate PM make observed with this technology.
It is clear that PM reduction efficiencies are limited by sulfur in
diesel fuel and that, in order to realize the PM emissions benefits
sought in this rule, diesel fuel sulfur levels must be as low as
possible. As discussed in Section IV, we believe that a 15 ppm sulfur
cap for highway diesel fuel is the correct level given consideration to
all factors. We request comment on the loss of PM control effectiveness
due to fuel sulfur along with supportive data.

c. Increased Maintenance Cost for Diesel Particulate Filters Due to
Sulfur

In addition to the direct performance and durability concerns
caused by sulfur in diesel fuel, it is also known that sulfur can lead
to increased maintenance costs, shortened maintenance intervals, and
poorer fuel economy for particulate filters. Diesel particulate filters
are highly effective at capturing the inorganic ash produced from
metallic additives in engine oil. This ash is accumulated in the filter
and is not removed through oxidation, unlike the trapped carbonaceous
PM. Periodically the ash must be removed by mechanical cleaning of the
filter with compressed air or water. This maintenance step is
anticipated to occur on intervals of well over one hundred thousand
miles. However, sulfur in diesel fuel increases this ash accumulation
rate through the formation of metallic sulfates in the filter, which
increases both the size and mass of the trapped ash. By increasing the
ash accumulation rate, the sulfur shortens the time interval between
the required maintenance of the filter and negatively impacts fuel
economy. We request comment on the issue of PM filter maintenance costs
and maintenance intervals along with supportive data.
2. Diesel NO_X Catalysts and the Need for Low-Sulfur Fuel
All of the NO_X exhaust emission control technologies
discussed previously in Section III are expected to utilize platinum to
oxidize NO to NO2 to improve the NO_X reduction
efficiency of the catalysts at low temperatures or as in the case of
the NO_X adsorber, as an essential part of the process of
NO_X storage. This reliance on NO2 as an integral
part of the reduction process means that the NO_X exhaust
emission control technologies, like the PM exhaust emission control
technologies, will have problems with sulfur in diesel fuel. In
addition NO_X adsorbers have the added constraint that the
adsorption function itself is blocked by the presence of sulfur. These
limitations due to sulfur in the fuel affect both overall performance
of the technologies and, in fact, the very feasibility of the
NO_X adsorber technology.

a. Sulfate Particulate Production for NO_X Control
Technologies

Two advanced NO_X control technologies that are likely to
be able to meet the NO_X emission standard being proposed
today are advanced NO_X adsorber catalyst systems and
advanced Compact-SCR systems. The NO_X adsorber technology
relies on an oxidation function to convert NO to NO2 over
the catalyst bed. For the NO_X adsorber this is a fundamental
step prior to the storage of NO2 in the catalyst bed as a
nitrate. Without this oxidation function the catalyst will only trap
that small portion of NO_X emissions from a diesel engine
which is NO2. This would reduce the NO_X adsorber
effectiveness for NO_X reduction from in excess of 90 percent
to something well below 20 percent. The NO_X adsorber relies
on platinum to provide this oxidation function due to the need for high
NO

[[Page 35476]]

oxidation rates under the relatively cool exhaust temperatures typical
of diesel engines.
The Compact-SCR technology, like the NO_X adsorber
technology, uses an oxidation catalyst to promote the oxidation of NO
to NO2 at the low temperatures typical of much of diesel
engine operation. By converting a portion of the NO_X
emissions to NO2 upstream of the ammonia SCR reduction
catalyst, the overall NO_X reductions are improved
significantly at low temperatures. As discussed previously in section
III, platinum group metals, primarily platinum, are known to be good
catalysts to promote NO oxidation, even at low temperatures. Therefore,
future Compact-SCR systems are expected to rely on a platinum oxidation
catalyst in order to provide the required NO_X emission
control.
The NO_X adsorber technology may be able to limit its
impact on sulfate PM emissions by releasing stored sulfur as
SO2 under rich operating conditions. The Compact-SCR
technology, on the other hand, has no means to limit sulfate emissions
other than through lower catalytic function or lowering sulfur in
diesel fuel. The degree to which the NO_X control
aftertreatment technologies increase the production of sulfate PM
through oxidation of SO2 to SO3 varies somewhat
from technology to technology, but it is expected to be similar in
magnitude and environmental impact to that for the PM control
technologies discussed previously. Thus, we believe that diesel fuel
sulfur levels will likely need to be below 15 ppm in order to apply
these advanced NO_X control technologies (see discussion in
section III.F.1). Without this low-sulfur fuel, the advanced
NO_X control technologies are expected to create PM emissions
in excess of the PM standard regardless of the engine-out PM levels. We
invite comment on sulfate PM production by NO_X control
technologies due to fuel sulfur along with supportive data.

b. Sulfur Poisoning (Sulfate Storage) on NO_X Adsorbers

The NO_X adsorber technology relies on the ability of the
catalyst to store NO_X as a nitrate on the surface of the
catalyst, or adsorber (storage) bed, during lean operation. Because of
the similarities in chemical properties of SO_X and
NO_X, the SO2 present in the exhaust is also
stored by the catalyst surface as a sulfate. The sulfate compound that
is formed is significantly more stable than the nitrate compound and is
not released and reduced during the NO_X release and
reduction step. Since the NO_X adsorber is essentially 100
percent effective at capturing SO2 in the adsorber bed, the
poisoning of the catalyst occurs rapidly. As a result, sulfate
compounds quickly occupy all of the NO_X storage sites on the
catalyst thereby rendering the catalyst ineffective for NO_X
reduction (poisoning the catalyst).
The stored sulfur compounds can be removed by exposing the catalyst
to hot (over 650 deg.C) and rich (air-fuel ratio below the
stoichiometric ratio of 14.5 to 1) conditions for a brief period.\115\
\116\ Under these conditions, the stored sulfate is released and
reduced in the catalyst.\117\ Because the exhaust must be taken to a
hot and rich condition, there is a fuel consumption impact associated
with the desulfation cycle. We have developed a spreadsheet model that
estimates the frequency of desulfation cycles from published data and
then estimates the fuel economy impact from this event.\118\ Table III-
F.2 shows the estimated fuel economy impact for desulfation of a
NO_X adsorber at different fuel sulfur levels assuming a
desired 90 percent NO_X conversion efficiency. The estimates
in the table are based on assumed average fuel sulfur levels associated
with different sulfur level caps.
---------------------------------------------------------------------------

\115\ [Reserved]
\116\ Dou, Danan and Bailey, Owen, ``Investigation of
NO_X Adsorber Catalyst Deactivation,'' SAE 982594.
\117\ Guyon, M. et al., ``Impact of Sulfur on NO_X
Trap Catalyst Activity--Study of the Regeneration Conditions,'' SAE
982607.
\118\ Memo from Byron Bunker, to docket A-99-06, ``Estimating
Fuel Economy Impacts of NO_X Adsorber De-Sulfurization.''

Table III.F-2.--Estimated Fuel Economy Impact From Desulfation of a 90%
Efficient NO_X Adsorber
------------------------------------------------------------------------
Fuel
Fuel sulfur cap [ppm] Average fuel economy
sulfur [ppm] penalty
------------------------------------------------------------------------
500.......................................... 350 27%
50........................................... 30 2%
25........................................... 15 1%
15........................................... 7 1%
5............................................ 2 1%
------------------------------------------------------------------------

The table highlights that the fuel economy penalty associated with
sulfur in diesel fuel is noticeable even at average sulfur levels as
low as 15 ppm and increases rapidly with higher sulfur levels. It also
shows that the use of a NO_X adsorber at the proposed 15 ppm
sulfur cap would be expected to result in a fuel economy impact of less
than 1 percent absent other changes in engine design. However, as
discussed in Section G below, we anticipate that other engine
modifications could be made to offset this fuel economy impact. For
example, a NO_X control device in the exhaust system could
allow use of fuel saving engine strategies, such as advanced fuel
injection timing, that could be used to offset the increased fuel
consumption associated with the NO_X adsorber. The result is
that low-sulfur fuel enables the NO_X adsorber, which in turn
enables fuel saving engine modifications. Such a system level fuel
economy impact, which we estimate to be zero under a 15 ppm cap
program, is discussed below in section III.G.
Future improvements in the NO_X adsorber technology are
expected and needed if the technology is to provide the environmental
benefits we have projected today. Some of these improvements are likely
to include improvements in the means and ease of removing stored sulfur
from the catalyst bed. However because the stored sulfate species are
inherently more stable than the stored nitrate compounds (from stored
NO_X emissions), we expect that a separate release and
reduction cycle (desulfation cycle) will always be needed in order to
remove the stored sulfur. Therefore, we believe that fuel with a sulfur
level at or below 15 ppm sulfur will be necessary in order to avoid an
unacceptable fuel economy impact. We request comment on sulfur
poisoning of NO_X adsorbers by fuel sulfur along with
supportive data.

c. Sulfur Impacts on Catalytic Efficiency

The technologies discussed in today's proposal generally rely on
some form of catalytic function in order to promote favorable chemical
reactions needed in order to accomplish the desired NO_X
emission reductions. In each case platinum and/or other precious group
metal catalysts are anticipated to be used to accomplish these
functions. From our experience with gasoline three-way catalysts and
from the extensive body of work in the literature we know that these
catalytic functions are inhibited by sulfur. Sulfur deposits on the
precious metal sites in the catalyst and causes a decrease in the
catalytic function of the device. This causes an increase in the light-
off temperature for the catalyst along with a significant reduction in
the oxidation and reduction efficiencies of all of the devices.\119\ As
discussed at length in the Tier 2 rulemaking, sulfur reductions in the
fuel are a very effective way to reduce catalyst poisoning of this type
in

[[Page 35477]]

order to maintain high catalyst efficiency and to ensure reliable
operation. We invite comment on fuel sulfur impact on catalyst
efficiency along with supportive data.
---------------------------------------------------------------------------

\119\ The Impact of Sulfur in Diesel Fuel on Catalyst Emissions
Control Technology--Manufacturers of Emission Controls Association
(MECA), March 15, 1999, www.meca.org.
---------------------------------------------------------------------------

3. What About Sulfur in Engine Lubricating Oils?
Current engine lubricating oils have sulfur contents which can
range from 2,500 ppm to as high as 8,000 ppm by weight. Since engine
oil is consumed by heavy-duty diesel engines in normal operation, it is
important that we account for the contribution of oil derived sulfur in
our analysis of the need for low-sulfur diesel fuel. One way to give a
straightforward comparison of this effect is to express the sulfur
consumed by the engine as an equivalent fuel sulfur level. This
approach requires that we assume specific fuel and oil consumption
rates for the engine. Using this approach, estimates ranging from two
to seven ppm diesel fuel sulfur equivalence have been made for the
sulfur contribution from engine oil.\120,\ \121\ If values at the upper
end of this range accurately reflect the contribution of sulfur from
engine oil to the exhaust this would be a concern as it would represent
50 percent of the total sulfur in the exhaust under a 15 ppm diesel
fuel sulfur cap (with an average sulfur level assumed to be
approximately seven ppm). However, we believe that this simplified
analysis, while valuable in demonstrating the need to investigate this
issue further, overstates the likely sulfur contribution from engine
oil by a significant amount.
---------------------------------------------------------------------------

\120\ Whitacre, Shawn. ``Catalyst Compatible'' Diesel Engine
Oils, DECSE Phase II, Presentation at DOE/NREL Workshop ``Exploring
Low Emission Diesel Engine Oils.'' January 31, 2000.
\121\ This estimate assumes that a heavy-duty diesel engine
consumes 1 quart of engine oil in 2,000 miles of operation, consumes
fuel at a rate of 1 gallon per 6 miles of operation and that engine
oil sulfur levels range from 2,000 to 8,000 ppm.
---------------------------------------------------------------------------

Current heavy-duty diesel engines operate with open crankcase
ventilation systems which ``consume'' oil by carrying oil from the
engine crankcase into the environment. This consumed oil is correctly
included in the total oil consumption estimates, but should not be
included in estimates of oil entering the exhaust system for this
analysis, since as currently applied this oil is not introduced into
the exhaust. At present we estimate that the majority of lube oil
consumed by an engine meeting the 0.1 g/bhp-hr PM standard is lost
through crankcase ventilation, rather than through the exhaust. Based
on assumed engine oil to PM conversion rates and historic soluble
organic fraction breakdowns we have estimated the contribution of
sulfur from engine oil to be less than two ppm fuel equivalency. With
the proposal today to close the crankcase, coupled with the use of
closed crankcase ventilation systems that separate in excess of 90
percent of the oil from the blow-by gases, we believe that this very
low contribution of lube oil to sulfur in the exhaust can be
maintained. For a further discussion of our estimates of the sulfur
contribution from engine oil refer to the draft RIA associated with
this proposal.
Although there are good indications to date that oil borne sulfur
is not a significant contributor to exhaust sulfur, EPA remains
concerned about this issue. We invite comment on the potential for
engine lubricating oils to introduce significant amounts of sulfur into
the exhaust. Of particular value to EPA is data indicating the expected
oil consumption rates of future engines and estimates of future engine
oil characteristics specifically with regard to sulfur content. We also
invite comment on the potential for new ``low-sulfur'' engine oils to
be developed for these vehicles equipped with sulfur sensitive emission
control technologies.

G. Fuel Economy Impact of Advanced Emission Control Technologies

The advanced emission control technologies expected to be applied
in order to meet the proposed NO_X and PM standards involve
wholly new system components integrated into engine designs and
calibrations, and as such may be expected to change the fuel
consumption characteristics of the overall engine design. After
reviewing the likely technology options available to the engine
manufacturers, we believe that the integration of the engine and
exhaust emission control systems into a single synergistic emission
control system will lead to heavy-duty vehicles which can meet
demanding emission control targets without increasing fuel consumption
beyond today's levels.
1. Diesel Particulate Filters and Fuel Economy
Diesel particulate filters are anticipated to provide a step-wise
decrease in diesel particulate (PM) emissions by trapping and oxidizing
the diesel PM. The trapping of the very fine diesel PM is accomplished
by forcing the exhaust through a porous filtering media with extremely
small openings and long path lengths.\122\ This approach results in
filtering efficiencies for diesel PM greater than 90 percent but
requires additional pumping work to force the exhaust through these
small openings. The additional pumping work is anticipated to increase
fuel consumption by approximately one percent.\123\ However, we believe
this fuel economy impact can be regained through optimization of the
engine-PM trap-NO_X adsorber system, as discussed below. We
request comment and data on the magnitude of the fuel economy impact of
diesel particulate filters.
---------------------------------------------------------------------------

\122\ Typically the filtering media is a porous ceramic monolith
or a metallic fiber mesh.
\123\ Engine, Fuel, and Emissions Engineering, Incorporated,
``Economic Analysis of Diesel Aftertreatment System Changes Made
Possible by Reduction of Diesel Fuel Sulfur Content,'' December 14,
1999, Air Docket A-99-06.
---------------------------------------------------------------------------

2. NO_X Control Technologies and Fuel Economy
NO_X adsorbers are expected to be the primary
NO_X control technology introduced in order to provide the
reduction in NO_X emissions envisioned in this proposal.
NO_X adsorbers work by storing NO_X emissions under
fuel lean operating conditions (normal diesel engine operating
conditions) and then by releasing and reducing the stored
NO_X emissions over a brief period of fuel rich engine
operation. This brief periodic NO_X release and reduction
step is directly analogous to the catalytic reduction of NO_X
over a gasoline three-way-catalyst. In order for this catalyst function
to occur the engine exhaust constituents and conditions must be similar
to normal gasoline exhaust constituents. That is, the exhaust must be
fuel rich (devoid of excess oxygen) and hot (over 250C). Although it is
anticipated that diesel engines can be made to operate in this way, it
is assumed that fuel economy while operating under these conditions
will be worse than normal. We have estimated that the fuel economy
impact of the NO_X release and reduction cycle would, all
other things being equal, increase fuel consumption by approximately
one percent. Again, we believe this fuel economy impact can be regained
through optimization of the engine-PM trap-NO_X adsorber
system, as discussed below.
In addition to the NO_X release and regeneration event,
another step in NO_X adsorber operation may affect fuel
economy. As discussed earlier, NO_X adsorbers are poisoned by
sulfur in the fuel even at the low sulfur levels we are proposing. As
discussed in the draft RIA, we anticipate that the sulfur poisoning of
the NO_X adsorber can be reversed through a periodic
``desulfation'' event. The desulfation of the NO_X adsorber
is accomplished in a similar manner to the NO_X release and
regeneration cycle described above. However it is anticipated that the

[[Page 35478]]

desulfation event will require extended operation of the diesel engine
at rich conditions.\124\ This rich operation will, like the
NO_X regeneration event, require an increase in the fuel
consumption rate and will cause an associated decrease in fuel economy.
With a 15 ppm fuel sulfur cap, we are projecting that fuel consumption
for desulfation would increase by one percent or less, which we believe
can be regained through optimization of the engine-PM trap-
NO_X adsorber system as discussed below.
---------------------------------------------------------------------------

\124\ Dou, D. and Bailey, O., ``Investigation of NO_X
Adsorber Catalyst Deactivation'' SAE982594.
---------------------------------------------------------------------------

While NO_X adsorbers require non-power producing
consumption of diesel fuel in order to function properly and,
therefore, have an impact on fuel economy, they are not unique among
NO_X control technologies in this way. In fact NO_X
adsorbers are likely to have a very favorable NO_X to fuel
economy trade-off when compared to other NO_X control
technologies like cooled EGR and injection timing retard that have
historically been used to control NO_X emissions. EGR
requires the delivery of exhaust gas from the exhaust manifold to the
intake manifold of the engine and causes a decrease in fuel economy for
two reasons. The first of these reasons is that a certain amount of
work is required to pump the EGR from the exhaust manifold to the
intake manifold; this necessitates the use of intake throttling or some
other means to accomplish this pumping. The second of these reasons is
that heat in the exhaust, which is normally partially recovered as work
across the turbine of the turbocharger, is instead lost to the engine
coolant through the cooled EGR heat exchanger. In the end, cooled EGR
is only some 50 percent effective at reducing NO_X.
Nonetheless, cooled EGR, which we anticipate to be the technology of
choice for meeting the proposed 2004 heavy-duty standards, still has a
considerable advantage over the previous solutions such as injection
timing retard. Injection timing retard is the strategy that has
historically been employed to control NO_X emissions. By
retarding the introduction of fuel into the engine, and thus delaying
the start of combustion, both the peak temperature and pressure of the
combustion event are decreased; this lowers NO_X formation
rates and, ultimately, NO_X emissions. Unfortunately, this
also significantly decreases the thermal efficiency of the engine
(decreases fuel economy) while also increasing PM emissions. As an
example, retarding injection timing eight degrees can decrease
NO_X emissions by 45 percent, but this occurs at a fuel
economy penalty of more than seven percent.\125\
---------------------------------------------------------------------------

\125\ Herzog, P. et al., NO_X Reduction Strategies for
DI Diesel Engines, SAE 920470, Society of Automotive Engineers 1992
(from Figure 1).
---------------------------------------------------------------------------

Today, most diesel engines rely on injection timing control
(retarding injection timing) in order to meet the 4.0 g/bhp-hr
NO_X emission standard. For 2002/2004 model year compliance,
we expect that engine manufacturers will use a combination of cooled
EGR and injection timing control to meet the 2.0 g/bhp-hr
NO_X standard. Because of the more favorable fuel economy
trade-off for NO_X control with EGR when compared to timing
control, we have forecast that less reliance on timing control will be
needed in 2002/2004. Therefore, fuel economy will not be changed even
at this lower NO_X level.
NO_X adsorbers have a significantly more favorable
NO_X to fuel economy trade-off when compared to cooled EGR or
timing retard alone, or even when compared to cooled EGR and timing
retard together.\126\ We expect NO_X adsorbers to be able to
accomplish greater than 90 percent reduction in NO_X
emissions, while only increasing fuel consumption by a very reasonable
two percent or less. Therefore, we expect manufacturers to take full
advantage of the NO_X control capabilities of the
NO_X adsorber and project that they will decrease reliance on
the more expensive (from a fuel economy standpoint) technologies,
especially injection timing retard. We would therefore predict, that
the fuel economy impact currently associated with NO_X
control from timing retard would be decreased by at least three
percent. In other words, through the application of advanced
NO_X exhaust emission control technologies, which are enabled
by the use of low-sulfur diesel fuel, we expect the NO_X
trade-off with fuel economy to continue to improve significantly when
compared to today's technologies. This will result in both much lower
NO_X emissions, and potentially overall improvements in fuel
economy. Improvements could easily offset the fuel consumption of the
NO_X adsorber itself and, in addition, the one percent fuel
economy loss projected to result from the application of PM filters.
Consequently, we are projecting no fuel economy penalty to result from
this rule. We invite comment and data concerning the relationships
between the various types of NO_X control technologies and
fuel economy as described here and in the cited references. In
particular we ask for comments and data on NO_X adsorber fuel
economy and methods of recovering that fuel economy through injection
timing changes.
---------------------------------------------------------------------------

\126\ Zelenka, P. et al., Cooled EGR--A Key Technology for
Future Efficient HD Diesels, SAE 980190, Society of Automotive
Engineers 1998. Figure 2 from this paper gives a graphical
representation of how new technologies (including aftertreatment
technologies) can shift the trade-off between NO_X
emissions and fuel economy.
---------------------------------------------------------------------------

3. Emission Control Systems for 2007 and Net Fuel Economy Impacts
We anticipate that, in order to meet the stringent NO_X
and PM emission standards proposed today, the manufacturers would
integrate engine-based emission control technologies and post-
combustion emission control technologies into a single systems-based
approach that would fundamentally shift historic trade-offs between
emissions control and fuel economy. As outlined in the preceding two
sections, individual components in this system would introduce new
constraints and opportunities for improvements in fuel efficient
control of emissions. Having considered the many opportunities to
fundamentally improve these relationships, we believe that it is
unlikely that fuel economy will be lower than today's levels and, in
fact, may improve through the application of these new technologies and
this new systems approach. Therefore, for our analysis of economic
impacts in section V, no penalty or benefit for changes to fuel economy
are considered. We request comment on our analysis of the likely fuel
economy offsets of the NO_X and PM emission control
technologies that would be needed in order to meet today's proposed
standards.

H. Future Reassessment of Diesel NO_X Control Technology

We are considering conducting a future reassessment of diesel
NO_X control technologies and associated fuel sulfur
requirements, and we request comment on the need for such a
reassessment. Given the relative state of development of NO_X
emission control technology versus PM and NMHC control technologies, we
would expect to focus the control technology reassessment solely on
NO_X control technologies. We believe that the clear intent
of this proposal to provide low-sulfur diesel fuel will allow the
development of this technology to progress rapidly, and will result in
systems capable of achieving the proposed standards. However, we
acknowledge that our proposed NO_X standard represents an
ambitious target for this technology, and that the degree of
uncertainty surrounding the feasibility of high-efficiency
NO_X control technology would be higher if

[[Continued on page 35479]]

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