Finding of Significant Contribution and Rulemaking for Certain States in the Ozone Transport Assessment Group Region for Purposes of Reducing Regional Transport of Ozone

Note: EPA no longer updates this information, but it may be useful as a reference or resource.

[Federal Register: October 27, 1998 (Volume 63, Number 207)]
[Rules and Regulations]
[Page 57355-57404]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr27oc98-14]
[[Page 57356]]

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ENVIRONMENTAL PROTECTION AGENCY
40 CFR Parts 51, 72, 75, and 96
[FRL-6171-2]
RIN 2060-AH10

Finding of Significant Contribution and Rulemaking for Certain
States in the Ozone Transport Assessment Group Region for Purposes of
Reducing Regional Transport of Ozone

AGENCY: Environmental Protection Agency (EPA).
ACTION: Final rule.

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SUMMARY: In accordance with the Clean Air Act (CAA), today's action is
a final rule to require 22 States and the District of Columbia to
submit State implementation plan (SIP) revisions to prohibit specified
amounts of emissions of oxides of nitrogen (NO_X)--one of the
precursors to ozone (smog) pollution--for the purpose of reducing
NO_X and ozone transport across State boundaries in the
eastern half of the United States.
Ground-level ozone has long been recognized, in both clinical and
epidemiological research, to affect public health. There is a wide
range of ozone-induced health effects, including decreased lung
function (primarily in children active outdoors), increased respiratory
symptoms (particularly in highly sensitive individuals), increased
hospital admissions and emergency room visits for respiratory causes
(among children and adults with pre-existing respiratory disease such
as asthma), increased inflammation of the lung, and possible long-term
damage to the lungs.
In today's action, EPA finds that sources and emitting activities
in each of the 22 States and the District of Columbia (23
jurisdictions) emit NO_X in amounts that significantly
contribute to nonattainment of the 1-hour and 8-hour ozone national
ambient air quality standards (NAAQS), or will interfere with
maintenance of the 8-hour NAAQS, in one or more downwind States.
Further, by today's action, EPA is requiring each of the affected
upwind jurisdictions (sometimes referred to as upwind States) to submit
SIP revisions prohibiting those amounts of NO_X emissions
which significantly contribute to downwind air quality problems. The
reduction of those NO_X emissions will bring NO_X
emissions in each of those States to within the resulting statewide
NO_X emissions budget levels established in today's rule. The
23 jurisdictions are: Alabama, Connecticut, Delaware, District of
Columbia, Georgia, Illinois, Indiana, Kentucky, Massachusetts,
Maryland, Michigan, Missouri, North Carolina, New Jersey, New York,
Ohio, Pennsylvania, Rhode Island, South Carolina, Tennessee, Virginia,
West Virginia, and Wisconsin. These States will be able to choose any
mix of pollution-reduction measures that will achieve the required
reductions.

EFFECTIVE DATES: This rule is effective December 28, 1998. The
incorporation by reference of certain publications listed in the
regulations is approved by the Director of the Federal Register as of
December 28, 1998.

ADDRESSES: Dockets containing information relating to this rulemaking
(Docket No. A-96-56 and Docket No. A-9-35) are available for public
inspection at the Air and Radiation Docket and Information Center
(6102), US Environmental Protection Agency, 401 M Street SW, room M-
1500, Washington, DC 20460, telephone (202) 260-7548, between 8:00 a.m.
and 4:00 p.m., Monday through Friday, excluding legal holidays. A
reasonable fee may be charged for copying.

FOR FURTHER INFORMATION CONTACT: General questions concerning today's
action should be addressed to Kimber S. Scavo, Office of Air Quality
Planning and Standards, Air Quality Strategies and Standards Division,
MD-15, Research Triangle Park, NC 27711, telephone (919) 541-3354; e-
mail: scavo.kimber@epa.gov. Please refer to SUPPLEMENTARY INFORMATION
below for a list of contacts for specific subjects described in today's
action.

SUPPLEMENTARY INFORMATION:

Availability of Related Information

Documents related to the Ozone Transport Assessment Group (OTAG)
are available on the Agency's Office of Air Quality Planning and
Standards' (OAQPS) Technology Transfer Network (TTN) via the web at
http://www.epa.gov/ttn/. If assistance is needed in accessing the
system, call the help desk at (919) 541-5384 in Research Triangle Park,
NC. Documents related to OTAG can be downloaded directly from OTAG's
webpage at http://www.epa.gov/ttn/otag/. The OTAG's technical data are
located at http://www.iceis.mcnc.org/OTAGDC. The notice of proposed
rulemaking for this final action, the supplemental notice of proposed
rulemaking, and associated documents are located at http://epa.gov/ttn/
oarpg/otagsip.html. Information related to Sections II, Weight of
Evidence Determination of Covered States, and IV, Air Quality
Assessment, can be obtained in electronic form from the following EPA
website: http://www.epa.gov/scram001/regmodcenter/t28.htm. Information
related to Section III, Determination of Budgets, may be found on the
following EPA website: http://www.epa.gov/capi. All information in
electronic form may also be found on diskettes that have been placed in
the docket to this rulemaking.

For Additional Information

For technical questions related to the air quality analyses, please
contact Norm Possiel; Office of Air Quality Planning and Standards;
Emissions, Monitoring, and Analysis Division; MD-14, Research Triangle
Park, NC 27711, telephone (919) 541-5692. For legal questions, please
contact Howard J. Hoffman, Office of General Counsel, 401 M Street SW,
MC-2344, Washington, DC 20460, telephone (202) 260-5892. For questions
concerning the statewide emissions budget revisions, please contact
Laurel Schultz; Office of Air Quality Planning and Standards;
Emissions, Monitoring, and Analysis Division; MD-14, Research Triangle
Park, NC 27711, telephone (919) 541-5511. For questions concerning SIP
reporting requirements, please contact Bill Johnson, Office of Air
Quality Planning and Standards, Air Quality Strategies and Standards
Division, MD-15, Research Triangle Park, NC 27711, telephone (919) 541-
5245. For questions concerning the model cap-and-trade rule, please
contact Rob Lacount, Office of Atmospheric Programs, Acid Rain
Division, MC-6204J, 401 M Street SW, Washington, DC 20460, telephone
(202) 564-9122. For questions concerning the regulatory cost analysis
of electricity generating sources, please contact Ravi Srivastava,
Office of Atmospheric Programs, Acid Rain Division, MC-6204J, 401 M
Street SW, Washington DC 20460, telephone (202) 564-9093. For questions
concerning the regulatory cost analysis of other stationary sources and
questions concerning the Regulatory Impact Analysis (RIA), please
contact Scott Mathias, Office of Air Quality Planning and Standards,
Air Quality Strategies and Standards Division, MD-15, Research Triangle
Park, NC 27711, telephone (919) 541-5310.

Outline

I. Background
A. Summary of Rulemaking and Affected States
B. General Factual Background
C. Statutory and Regulatory Background
1. CAA Provisions
a. 1970 and 1977 CAA Amendments
b. 1990 CAA Amendments
2. Regulatory Structure
a. March 2, 1995 Policy
b. OTAG

[[Page 57357]]

c. EPA's Transport SIP Call Regulatory Efforts
d. Revision of the Ozone NAAQS
D. Section 126 Petitions
E. OTAG
F. Discussion of Comment Period and Availability of Key Information
1. Request for Extension of the Comment Period
2. Request for Time to Conduct Additional Modeling
3. Availability of Key Information
4. Public Hearings
G. Implementation of Revised Air Quality Standards
H. Summary of Major Changes between Proposals and Final Rule
1. EPA's Analytical Approach (Section II.A)
2. Cost Effectiveness of Emissions Reductions (Section II.D)
3. Determination of Budgets (Section III)
4. NO_X Control Implementation and Budget Achievement
Dates (Section V)
5. SIP Criteria (Section VI.A)
6. Emissions Reporting Requirements for States (Section VI.B)
7. NO_X Budget Trading Program (Section VII)
8. Interaction with Title IV NO_X Rule (Section VIII)
9. Administrative Requirements (Section X)
II. EPA's Analytical Approach
A. Interpretation of the CAA's Transport Provisions
1. Authority and Process for Requiring SIP Submissions under the
1-Hour Ozone NAAQS
a. Authority for Requiring SIP Submissions under the 1-Hour NAAQS
b. Process for Requiring SIP Submissions under the 1-Hour NAAQS
2. Authority and Process for Requiring SIP Submissions under the
8-Hour Ozone NAAQS
a. Authority for Requiring SIP Submissions under the 8-Hour NAAQS
b. Process for Requiring SIP Submissions under the 8-hour Standard
3. Requirements of Section 110(a)(2)(D)
a. Summary
b. Determination of Meaning of ``Nonattainment'
c. Definition of Significant Contribution
d. Multi-factor Test for Determining Significant Contribution
e. Air Quality Factors
f. Determination of Highly Cost-effective Reductions and of Budgets
g. Other Considerations in Determination of Significant
Contribution
h. Interfere with Maintenance
i. Dates
j. Downwind Areas' Control Obligations
k. Section 110(a)(2)(D) Caselaw
B. Alternative Interpretation of Section 110(a)(2)(D)
C. Weight-of-Evidence Determination of Covered States
1. Major Findings from OTAG-Related Technical Analyses
2. Summary of Notice of Proposed Rulemaking Weight-of-Evidence
Approach
a. Quantification of Contributions
b. Evaluation of 1-Hour and 8-Hour Contributions
c. Comments and Responses on Proposed Weight-of-Evidence
Approach to Significant Contribution
3. Analysis of State-specific Air Quality Factors
a. Overall Nature of Ozone Problem (``Collective Contribution'')
b. Extent of Downwind Nonattainment Problems
c. Air Quality Impacts of Upwind Emissions on Downwind Nonattainment
4. Confirmation of States Making a Contribution to Downwind
Nonattainment
a. Analysis Approach
b. States Which Contain Sources That Significantly Contribute to
Downwind Nonattainment
c. Examples of Contributions From Upwind States to Downwind
Nonattainment
d. Conclusions From Air Quality Evaluation of Downwind Contributions
5. States Not Covered by This Rulemaking
D. Cost Effectiveness of Emissions Reductions
1. Sources Included in the Cost-Effectiveness Determination
a. Electricity Generating Boilers and Turbines
b. Other Stationary Sources
2. Sources Not Included in the Cost-Effectiveness Determination
a. Area Sources
b. Small Point Sources
c. Mobile Sources
d. Other Stationary Sources
e. Conclusion
E. Other Considerations
1. Consistency of Regional Reductions with Attainment Needs of
Downwind Areas
a. General Discussion
b. 8-hour Nonattainment Problems
c. Commenters' Concerns
2. Equity Considerations
3. General Cost Considerations
4. Conclusion
III. Determination of Budgets
A. General Comments on the Base Emission Inventory
1. Quality
2. Availability
B. Electricity Generating Units (EGUs)
1. Base Inventory
2. Growth
a. Growth Rates
b. Use of IPM
c. Use of ``Corrected'' Growth Rates
3. Budget Calculation
a. Input vs. Output
b. Alternative Emission Limits
c. Consideration of the Climate Change Action Plan
C. Non-EGU Point Sources
1. Base Inventory
2. Growth
3. Budget Calculation
a. Proposed Control Assumptions
b. Small Source Exemption
c. Exemptions for Other Non-EGU Point Sources
d. Sources Without Adequate Control Information
e. Case-By-Case Analysis of Control Measures
f. Cost Effectiveness
g. Industrial Boiler Control Costs
h. Cement Manufacturing
i. Stationary Internal Combustion Engines
j. Industrial Boilers and Turbines
k. Municipal Waste Combustors (MWCs)
D. Highway Mobile Sources
1. Base Inventory
2. Growth
3. Budget Calculation
a. I/M Program Coverage
b. Emissions Cap
c. Tier 2 Standards
d. Low Sulfur Fuel
e. Conformity
E. Stationary Area and Nonroad Mobile Sources
1. Base Inventory
2. Growth
3. Budget Calculation
F. Other Budget Issues
1. Uniform vs. Regional Controls
2. Seasonal vs. Annual Controls
3. Full vs. Partial States
4. NOx Waivers
5. Recalculation of Budgets
6. Compliance Supplement Pool
a. Size of the Compliance Supplement Pool
b. State Distribution of the Compliance Supplement Pool
7. Banking
a. Banking Starting in 2003
b. Management of Banked Allowances
c. Early Reduction Credits
G. Final Statewide Budgets
1. EGU
a. Description of Selected Approach
b. Summary of Budget Component
2. Non-EGU Point Sources
a. Description of Selected Approach
b. Summary of Budget Component
3. Mobile and Area Sources
a. Description of Selected Budget Approach
b. Summary of Budget Component
4. Potential Alternatives to Meeting the Budget
5. Statewide Budgets
IV. Air Quality Assessment
A. Assessment of Proposed Statewide Budgets
B. Comments and Responses
C. Assessment of Alternative Control Levels
1. Scenarios Modeled
2. Emissions for Model Runs
3. Modeling Results
a. Impacts of Alternative Controls
b. Impacts of Upwind Controls on Downwind Nonattainment
c. Summary of Findings
V. NOx Control Implementation and Budget Achievement Dates
A. NOx Control Implementation Date
1. Practicability
a. Combustion Controls
b. Post-Combustion Controls
2. Relationship to SIP Submittal Date
3. Rationale
B. Budget Achievement Date
VI. SIP Criteria and Emissions Reporting Requirements
A. SIP Criteria
1. Schedule for SIP Revision
2. Approvability Criteria
a. Source Categories Subject to Additional Approvability Criteria

[[Page 57358]]

b. Pollution Abatement Requirements
c. Monitoring Requirements
d. Approvability of Trading Program
3. Sanctions
4. FIPs
B. Emissions Reporting Requirements for States
1. Use of Inventory Data
2. Response to Comments
3. Final Rule
4. Data Elements to be Reported
5. 2007 Report
6. Ozone Season Reporting
7. Data Reporting Procedures
8. Confidential Data
C. Timeline
VII. NO_X Budget Trading Program
A. General Background
B. NO_X Budget Trading Program Rulemaking Overview
C. General Design of NO_X Budget Trading Program
1. Appropriateness of Trading Program
2. Alternative Market Mechanisms
3. State Adoption of Model Rule
a. Process for Adoption
b. Model Rule Variations
4. Unrestricted Trading Market
a. Geographic Issues
b. Episodic Issues
D. Applicability
1. Core Sources
a. Commenters Who Felt the Core Group Should Not Be Changed
b. Commenters Who Felt the Core Group Should Be Expanded
c. Commenters Who Felt the Core Group Is Overly Inclusive
2. Mobile/Area Sources
3. Monitoring
a. Use of Part 75 to Ensure Compliance with the NO_X
Budget Trading Program
b. Use of CEMS on Large Units
c. Commenters Who do not Believe that CEMS are Necessary
d. Issues Related to Monitoring and Reporting Needed to Support
a Heat Input Allocation Methodology
e. Amendments to Part 75
E. Emission Limitations/Allowance Allocations
1. Timing Requirements
2. Options for NO_X Allowance Allocation Methodology
3. New Source Set-Aside
4. Optional NO_X Allocation Methodology in Model Rule
F. Banking Provisions
1. Banking Starting in 2003
2. Management of Banked Allowances
3. Early Reduction Credits
4. Optional Methodology for Issuing Early Reduction Credits
5. Integrating the OTC Program with the NO_X Budget
Trading Program's Banking Provisions
G. New Source Review
VIII. Interaction with Title IV NO_X Rule
IX. Non-Ozone Benefits of NO_X Emissions Decreases
A. Summary of Comments
B. Response to Comments
1. Drinking Water Nitrate
2. Eutrophication
3. Regulatory Impact Analysis
4. Justification for Rulemaking
X. Administrative Requirements
A. Executive Order 12866: Regulatory Impact Analysis
B. Regulatory Flexibility Act: Small Entity Impacts
C. Unfunded Mandates Reform Act
D. Paperwork Reduction Act
E. Executive Order 13045: Protection of Children from
Environmental Health Risks and Safety Risks
1. Applicability of E.O. 13045
2. Children's Health Protection
F. Executive Order 12898: Environmental Justice
G. Executive Order 12875: Enhancing the Intergovernmental Partnerships
H. Executive Order 13084: Consultation and Coordination with
Indian Tribal Governments
I. Judicial Review
J. Congressional Review Act
K. National Technology Transfer and Advancement Act

Appendix A--Detailed Discussion of Changes to Part 75

CFR Revisions and Additions

Part 51
Sec. 51.121
Sec. 51.122
Part 72
Part 75
Part 96

I. Background

A. Summary of Rulemaking and Affected States

By notice of proposed rulemaking (NPR, proposal, or ``proposed SIP
call'') (62 FR 60318, November 7, 1997) and by supplemental notice
(SNPR or supplemental proposal) (63 FR 25902, May 11, 1998), EPA
proposed to find that NO_X emissions from sources and
emitting activities (sources) in 23 jurisdictions (hereinafter also
referred to as States) will significantly contribute to nonattainment
of the 1-hour and 8-hour ozone NAAQS, or will interfere with
maintenance of the 8-hour NAAQS, in one or more downwind States
throughout the Eastern United States. The EPA based these proposals on
data generated by OTAG, public comments, and other relevant
information. Today's final action confirms that proposed finding. It
also requires, under CAA section 110(a)(1) and 110(k)(5), that the 23
jurisdictions adopt and submit SIP revisions that, in order to assure
that their SIPs meet the requirements of section 110(a)(2)(D)(i)(I),
contain provisions adequate to prohibit sources in those States from
emitting NO_X in amounts that ``contribute significantly to
nonattainment in, or interfere with maintenance by,'' a downwind State.
The 23 jurisdictions are: Alabama, Connecticut, Delaware, District of
Columbia, Georgia, Illinois, Indiana, Kentucky, Massachusetts,
Maryland, Michigan, Missouri, North Carolina, New Jersey, New York,
Ohio, Pennsylvania, Rhode Island, South Carolina, Tennessee, Virginia,
West Virginia, and Wisconsin.
Each of these States and the District of Columbia is required to
adopt and submit by September 30, 1999, a SIP revision. The SIP
revision must contain measures that will assure that sources in the
State reduce their NO_X emissions sufficiently to eliminate
the amounts of NO_X emissions that contribute significantly
to nonattainment, or that interfere with maintenance, downwind. By
eliminating these amounts of NO_X emissions, the control
measures will assure that the remaining NO_X emissions will
meet the level identified in today's rule as the State's NO_X
emissions budget. For simplicity, this final rule may refer to the
amounts that such SIP provisions must prohibit in order to meet the
statute as the ``significant amounts'' of NO_X emissions.
After prohibiting these significant amounts of NO_X, the
remaining amounts emitted by sources in the covered States will not
``significantly contribute to nonattainment, or interfere with
maintenance by,'' a downwind State, under section 110(a)(2)(D)(i)(I).
Section II.C, Weight-of-Evidence Determination of Covered States,
describes how EPA determined which States include sources that emit
NO_X in amounts of concern (the ``covered'' States), and
Sections II.D, Cost Effectiveness of Emissions Reductions; II.E,
Comparison of Upwind and Downwind Costs; and III, Determination of
Budgets, describe how EPA determined the significant amounts of
emissions and the resulting statewide emissions budgets for the States
identified above. Section IV, Air Quality Assessment, discusses air
quality analyses conducted by EPA which help confirm the decisions and
requirements set forth in this rulemaking. Section V, NO_X
Control Implementation and Budget Achievement Dates, primarily
discusses the dates by which (1) the States must submit SIP revisions
in response to today's action, (2) the sources must implement the
measures the States choose for the purpose of prohibiting the
significant amounts of NO_X, and (3) the States are projected
to achieve the budget levels. Section VI, SIP Criteria and Emissions
Reporting Requirements, describes the SIP requirements themselves.
The SIP requirements permit each State to determine what measures
to adopt to prohibit the significant amounts and hence meet the
necessary emissions budget. Consistent with OTAG's recommendations to
achieve

[[Page 57359]]

NO_X emissions decreases primarily from large stationary
sources in a trading program, EPA encourages States to consider
electric utility and large boiler controls under a cap-and-trade
program as a cost-effective strategy. The recommended cap-and-trade
program is described in more detail in Section VII, NO_X
Budget Trading Program. The EPA also recognizes that promotion of
energy efficiency can contribute to a cost-effective strategy. In
Section VIII, Interaction with Title IV NO_X rule, EPA
explains that it is not adopting proposed revisions to the title IV
NO_X rule concerning the relationship between this rulemaking
and the title IV NO_X rule. The remaining parts of today's
action include Section IX, Non-Ozone Benefits of NO_X
Reductions, and Section X, Administrative Requirements.
The EPA also conducted a RIA which is available in the docket to
this rulemaking as a technical support document (TSD), entitled
``Regulatory Impact Analysis for the Regional NO_X SIP Call''
(docket no. VI-B-09). A detailed explanation of how EPA calculated the
budgets is also available as a TSD entitled ``Development of Modeling
Inventory and Budgets for the Regional NO_X SIP Call''
(docket no. VI-B-10). These two TSDs have been revised for the final
rulemaking. A detailed explanation of the air quality modeling analyses
is also available, entitled ``Air Quality Modeling Technical Support
Document for the Regional NO_X SIP Call'' (docket no. VI-B-
11) for this final rulemaking. This preamble for today's notice
responds to some of the comments, but another document, entitled
``Response to Significant Comments on the Finding of Significant
Contribution and Rulemaking for Certain States in the OTAG Region for
Purposes of Reducing Regional Transport of Ozone,'' is included in the
docket (docket no. VI-C-01).

B. General Factual Background

In today's action, EPA takes a significant step toward reducing
ozone in the eastern half of the country. Ground-level ozone, the main
harmful ingredient in smog, is produced in complex chemical reactions
when its precursors, volatile organic compounds (VOC) and
NO_X, react in the presence of sunlight. The chemical
reactions that create ozone take place while the pollutants are being
blown through the air by the wind, which means that ozone can be more
severe many miles away from the source of emissions than it is at the
source.
The science of ozone formation, transport, and accumulation is
complex. Ozone is produced and destroyed in a cyclical set of chemical
reactions involving NO_X, VOC and sunlight. Emissions of
NO_X and VOC are necessary for the formation of ozone in the
lower atmosphere. In part of the cycle of reactions, ozone
concentrations in an area can be lowered by the reaction of nitric
oxide with ozone, forming nitrogen dioxide; as the air moves downwind
and the cycle continues, the nitrogen dioxide forms additional ozone.
The importance of this reaction depends, in part, on the relative
concentrations of NO_X, VOC and ozone, all of which change
with time and location.
At ground level, ozone can cause a variety of ill effects to human
health, crops and trees. Specifically, ground-level ozone has been
shown in clinical and/or epidemiologial studies to have the following
health effects:

' Decreased lung function, primarily in children active outdoors
' Increased respiratory symptoms, particularly in
highly sensitive individuals
' Hospital admissions and emergency room visits for
respiratory causes among children and adults with pre-existing
respiratory disease such as asthma
' Inflammation of the lung
' Possible long-term damage to the lungs or even premature death.

The new 8-hour primary ambient air quality standard (62 FR 38856,
July 18, 1997) will provide increased protection to the public from
these health effects.
Each year, ground-level ozone above background is also responsible
for significant agricultural crop yield losses. Ozone also causes
noticeable foliar damage in many crops, trees, and ornamental plants
(i.e., grass, flowers, shrubs, and trees) and causes reduced growth in
plants. Studies indicate that current ambient levels of ozone are
responsible for damage to forests and ecosystems (including habitat for
native animal species).
As part of the efforts to reduce harmful levels of smog, EPA,
today, is establishing a requirement for certain States to revise their
SIPs in order to implement the necessary regional-scale reductions in
NO_X emissions, and, thereby, reduce transported
NO_X and ozone. Since air pollution travels across county and
State lines, it is essential for State governments and air pollution
control agencies to cooperate to solve the problem.
Currently, the following areas, impacted by the 23 jurisdictions
that are the subject of today's rulemaking, are designated
nonattainment areas for ozone under the 1-hour NAAQS:

Atlanta, GA
Baltimore, MD
Birmingham, AL
Boston-Lawrence-Worcester (eastern MA), MA-NH
Chicago-Gary-Lake County, IL-IN
Cincinnati-Hamilton, OH-KY
Door County, WI
Greater Connecticut
Kent & Queen Anne's Counties, MD
Lancaster, PA
Louisville, KY-IN
Manitowoc County, WI
Milwaukee-Racine, WI
Muskegon, MI
New York-Northern New Jersey-Long Island, NY-NJ-CT
Philadelphia-Wilmington-Trenton, PA-NJ-DE-MD
Pittsburgh-Beaver Valley, PA
Portland, ME
Portsmouth-Dover-Rochester, NH
Providence (All RI), RI
St. Louis, MO-IL
Springfield (western MA), MA
Washington, DC-MD-VA

These areas include many of the major urban centers in the eastern
half of the Nation. The combined population for these areas is
approximately 61.5 million. As described elsewhere, the reductions
called for in today's action will reduce ozone levels throughout these
areas.
Many more areas currently violate the 8-hour NAAQS. The EPA
estimates that a total population of approximately 73 million in the 23
jurisdictions live in counties for which air quality is monitored to be
in violation of that NAAQS. The reductions called for in today's action
will reduce ozone levels throughout these areas as well.
Moreover, as discussed below, many of these areas are expected to
be classified as ``transitional,'' which means, in most cases, that
they are expected to come into attainment solely as a result of the
reductions required by today's action. Thus, for those who live in
these areas, the reductions required under today's action, in-and-of-
themselves, are expected to mean the difference between unhealthful
ozone levels and acceptable ozone levels.
Please note that EPA will not designate ozone nonattainment areas
for the 8-hour NAAQS until 2000, and these designations will be based
on the data that are most recently available at that time.

C. Statutory and Regulatory Background

1. CAA Provisions
a. 1970 and 1977 CAA Amendments. For almost 30 years, Congress has
focused major efforts on curbing ground-level ozone. In 1970, Congress
amended the CAA to require, in title I, that EPA issue, and
periodically review

[[Page 57360]]

and if necessary revise, NAAQS for ubiquitous air pollutants (sections
108 and 109). Congress required the States to submit SIPs to attain and
maintain those NAAQS, and Congress included, in section 110, a list of
minimum requirements that SIPs must meet. Congress anticipated that
areas would attain the NAAQS by 1975.
In 1977, Congress amended the CAA by providing, among other things,
additional time for areas that were not attaining the ozone NAAQS to do
so, as well as by imposing specific SIP requirements for those
nonattainment areas. These provisions first required the designation of
areas as attainment, nonattainment, or unclassifiable, under section
107; and then required that SIPs for ozone nonattainment areas include
the additional provisions set out in part D of title I, as well as
demonstrations of attainment of the ozone NAAQS by either 1982 or 1987
(section 172).
In addition, the 1977 Amendments included two provisions focused on
interstate transport of air pollutants: the predecessor to current
section 110(a)(2)(D), which requires SIPs for all areas to constrain
emissions with certain adverse downwind effects; and section 126,
which, in general, authorizes a downwind State to petition EPA to
impose limits directly on upwind sources found to adversely affect that
State. Section 110(a)(2)(D), which is key to the present action, is
described in more detail below.
b. 1990 CAA Amendments. In 1990, Congress amended the CAA to better
address, among other things, continued nonattainment of the 1-hour
ozone NAAQS; the requirements that would apply if EPA revised the 1-
hour standard; and transport of air pollutants across State boundaries
(Pub. L. 101-549, Nov. 15, 1990, 104 Stat. 2399, 42 U.S.C., 7401-
7671q). Numerous provisions added, or revised, by the 1990 Amendments
are relevant to today's proposal.
(1) 1-Hour Ozone NAAQS. In the 1990 Amendments, Congress required
the States and EPA to review and, if necessary, revise the designation
of areas as attainment, nonattainment, and unclassifiable under the
ozone NAAQS in effect at that time, which was the 1-hour standard
(section 107(d)(4)). Areas designated as nonattainment were divided
into, primarily, five classifications based on air quality design
values (section 181(a)(1)). Each classification carries specific
requirements, including new attainment dates (sections 181-182). In
increasing severity of the air quality problem, these classifications
are marginal, moderate, serious, severe and extreme. The OTAG region
includes nonattainment areas of all classifications except extreme.
As amended in 1990, the CAA requires States containing ozone
nonattainment areas classified as moderate or above to submit several
SIP revisions at various times. One set of SIP revisions included
specified control measures, such as reasonably available control
technology (RACT) for existing VOC and NO_X sources (section
182(b)(2), 182(f)). In addition, the CAA requires the reduction of VOC
in the amount of 15 percent by 1996 from a 1990 baseline (section
182(b)(1)). Further, for nonattainment areas classified as serious and
above, the CAA requires the reduction of VOC or NO_X
emissions in the amount of 9 percent over each 3-year period from 1996
through the attainment date (the rate-of-progress (ROP) SIP
submittals), under section 182(c)(2)(B). In addition, the CAA requires
a demonstration of attainment, including air quality modeling, for the
nonattainment area (the attainment demonstration), as well as SIP
measures containing any additional reductions that may be necessary to
attain by the applicable attainment date (section 182(c)-(e)). The CAA
established November 15, 1994 as the required date for the ROP and
attainment demonstration SIP submittals for areas classified as serious
and above.¹
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\1\ For moderate ozone nonattainment areas, the attainment
demonstration was due November 15, 1993 (section 182(b)(1)(A)),
except that if the State elected to conduct an urban airshed model,
EPA allowed an extension to November 15, 1994.
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(2) Revised NAAQS. Section 109(d) of the CAA requires periodic
review and, if appropriate, revision of the NAAQS. As amended in 1990,
the CAA further requires EPA to designate areas as attainment,
nonattainment, and unclassifiable under a revised NAAQS (section
107(d)(1); section 6103, Pub. L. 105-178). The CAA authorizes EPA to
classify areas that are designated nonattainment under the new NAAQS
and to establish for those areas attainment dates that are as
expeditiously as practicable, but not to exceed 10 years from the date
of designation (section 172(a)).
(3) General Requirements. The CAA continues, in revised form,
certain requirements, dating from the 1970 Amendments, which pertain to
all areas, regardless of their designation. All areas are required to
submit SIPs within certain timeframes (section 110(a)(1)), and those
SIPs must include specified provisions, under section 110(a)(2). In
addition, SIPs for nonattainment areas are generally required to
include additional specified control requirements, as well as controls
providing for attainment of any revised NAAQS and periodic reductions
providing ``reasonable further progress'' in the interim (section 172(c)).
(4) Provisions Concerning Transport of Ozone and Its Precursors.
The 1990 Amendments reflect general awareness by Congress that ozone is
a regional, and not merely a local, problem. As described above, ozone
and its precursors may be transported long distances across State lines
to combine with ozone and precursors downwind, thereby exacerbating the
ozone problems downwind. The phenomenon of ozone transport was not
generally recognized until relatively recently. Yet, ozone transport is
a major reason for the persistence of the ozone problem,
notwithstanding the imposition of numerous controls, both Federal and
State, across the country.
Section 110(a)(2)(D) provides one of the most important tools for
addressing the problem of transport. This provision, which applies by
its terms to all SIPs for each pollutant covered by a NAAQS, and for
all areas regardless of their attainment designation, provides that a
SIP must contain adequate provisions prohibiting its sources from
emitting air pollutants in amounts that will contribute significantly
to nonattainment, or interfere with maintenance, in one or more
downwind States.
Section 110(k)(5) authorizes EPA to find that a SIP is
substantially inadequate to meet any CAA requirement. If EPA makes such
a finding, it must require the State to submit, within a specified
period, a SIP revision to correct the inadequacy.
The CAA further addresses interstate transport of pollution in
section 126, which Congress revised slightly in 1990. Subsection (b) of
that provision authorizes each State (or political subdivision) to
petition EPA for a finding designed to protect that entity from upwind
sources of air pollutants.²
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\2\ In addition, section 115 authorizes EPA to require a SIP
revision when one or more sources within a State ``cause or
contribute to air pollution which may reasonably be anticipated to
endanger public health or welfare in a foreign country.''
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In addition, the 1990 Amendments added section 184, which
delineates a multistate ozone transport region (OTR) in the Northeast,
requires specific additional controls for all areas (not only
nonattainment areas) in that region, and establishes the Ozone
Transport Commission (OTC) for the purpose of recommending to EPA
regionwide controls affecting all areas in that region. At the same
time, Congress added section 176A, which authorizes

[[Page 57361]]

the formation of transport regions for other pollutants and in other
parts of the country.
2. Regulatory Structure
a. March 2, 1995 Policy. Notwithstanding significant efforts, the
States generally were not able to meet the November 15, 1994 statutory
deadline for the attainment demonstration and ROP SIP submissions
required under section 182(c). The major reason for this failure was
that at that time, States with downwind nonattainment areas were not
able to address transport from upwind areas. As a result, in a
memorandum from Mary D. Nichols, Assistant Administrator for Air and
Radiation, dated March 2, 1995, entitled ``Ozone Attainment
Demonstrations,'' (March 2, 1995 Memorandum or the Memorandum), EPA
recognized the efforts made by States and the remaining difficulties in
making the ROP and attainment demonstration submittals. The EPA
recognized that development of the necessary technical information, as
well as the control measures necessary to achieve the large level of
reductions likely to be required, had been particularly difficult for
the States affected by ozone transport.
Accordingly, as an administrative remedial matter, the Memorandum
indicated that EPA would establish new timeframes for SIP submittals.
The Memorandum indicated that EPA would divide the required SIP
submittals into two phases. Phase I generally consisted of (i) SIP
measures providing for ROP reductions due by the end of 1999, (ii) an
enforceable SIP commitment to submit any remaining required ROP
reductions on a specified schedule after 1996, and (iii) an enforceable
SIP commitment to submit the additional SIP measures needed for
attainment. Phase II consists of the remaining submittals, beginning in
1997.
The Phase II submittals primarily consisted of the remaining ROP
SIP measures, the attainment demonstration and additional rules needed
to attain, and any regional controls needed for attainment by all areas
in the region. The March 2, 1995 Memorandum indicated that the
attainment demonstration, target calculations for the post-1999 ROP
milestones, and identification of rules needed to attain and for post-
1999 ROP were due in mid-1997. To allow time for States to incorporate
the results of the OTAG modeling into their local plans, EPA extended
the mid-1997 submittal date to April 1998.³
---------------------------------------------------------------------------

\3\ Guidance for Implementing the 1-hour Ozone and Pre-Existing
PM10 NAAQS, Memorandum from Richard D. Wilson, dated December 29,
1997.
---------------------------------------------------------------------------

b. OTAG. In addition, the March 2, 1995 Memorandum called for an
assessment of the ozone transport phenomenon. The Environmental Council
of the States (ECOS) had recommended formation of a national work group
to allow for a thoughtful assessment and development of consensus
solutions to the problem. The OTAG was a partnership between EPA, the
37 easternmost States and the District of Columbia, industry
representatives, and environmental groups. The OTAG's air quality
modeling and recommendations formed the basis for today's action.
c. EPA's Transport SIP Call Regulatory Efforts. Shortly after OTAG
began its work, EPA began to indicate that it intended to issue a SIP
call to require States to implement the reductions necessary to address
the ozone transport problem. On January 10, 1997 (62 FR 1420), EPA
published a notice of intent that articulated this goal and indicated
that before taking final action, EPA would carefully consider the
technical work and any recommendations of OTAG. The EPA published the
NPR for the NO_X SIP call by notice dated November 7, 1997
(62 FR 60319). The NPR proposed to make a finding of significant
contribution due to transported NO_X emissions to
nonattainment or maintenance problems downwind and to assign
NO_X emissions budgets for 23 jurisdictions. The EPA
published a supplemental notice of proposed rulemaking (SNPR) by notice
dated May 11, 1998 (63 FR 25902) which proposed a model NO_X
budget trading program and State reporting requirements and provided
the air quality analyses of the proposed statewide NO_X
emissions budgets. The EPA received approximately 700 comments on these
proposals. The comment periods are described in Section I.F, Discussion
of Comment Period and Availability of Key Information. Throughout the
course of the rulemaking, EPA has added information to the docket. By
notice dated August 24, 1998 (63 FR 45032), EPA published a notice of
availability listing the additional documents placed in the docket.
d. Revision of the Ozone NAAQS. On July 18, 1997 (62 FR 38856), EPA
issued its final action to revise the NAAQS for ozone. The EPA's
decision to revise the standard was based on the Agency's review of the
available scientific evidence linking exposures to ambient ozone to
adverse health and welfare effects at levels allowed by the pre-
existing 1-hour ozone standards. The 1-hour primary standard was
replaced by an 8-hour standard at a level of 0.08 parts per million
(ppm), with a form based on the 3-year average of the annual fourth-
highest daily maximum 8-hour average ozone concentration measured at
each monitor within an area. The new primary standard will provide
increased protection to the public, especially children and other at-
risk populations, against a wide range of ozone-induced health effects.
Health effects are described in paragraph I.B, General Factual
Background. The EPA retained the applicability of the 1-hour NAAQS for
existing nonattainment areas until such time as EPA determines that an
area has attained the 1-hour NAAQS (40 CFR 50.9(b)).
The pre-existing 1-hour secondary ozone standard was replaced by an
8-hour standard identical to the new primary standard. The new
secondary standard will provide increased protection to the public
welfare against ozone-induced effects on vegetation.

D. Section 126 Petitions

In a separate rulemaking, EPA is proposing action on petitions
submitted by eight northeastern States under section 126 of the CAA.
Each petition specifically requests that EPA make a finding that
NO_X emissions from certain major stationary sources
significantly contribute to ozone nonattainment problems in the
petitioning State. The eight States are Connecticut, Massachusetts,
Maine, New Hampshire, New York, Pennsylvania, Rhode Island, and Vermont.
Both the NO_X SIP call and the section 126 petitions are
designed to address ozone transport through reductions in upwind
NO_X emissions. However, the EPA's response to the section
126 petitions differs from EPA's action in the NO_X SIP call
rulemaking in several ways. In today's NO_X SIP call, EPA is
determining that certain States are or will be significantly
contributing to nonattainment or maintenance problems in downwind
States. The EPA is requiring the upwind States to submit SIP provisions
to reduce the amounts of each State's NO_X emissions that
significantly contribute to downwind air quality problems. The States
will have the discretion to select the mix of control measures to
achieve the necessary reductions. By contrast, under section 126, if
findings of significant contribution are made for any sources
identified in the petitions, EPA would determine the necessary emissions

[[Page 57362]]

limits to address the amount of significant contribution and would
directly regulate the sources. A section 126 remedy would apply only to
sources in States named in the petitions.
Based on the view that the SIP call and section 126 petitions are
both designed to achieve the same goal, several commenters urged EPA to
coordinate the two actions to the maximum extent possible. The EPA
agrees that the two actions are closely related and, therefore, should
be coordinated. This will help provide certainty for State and business
planning requirements. In addition, this coordination can help to
facilitate a trading program among sources in SIP call States that
choose to participate in the NO_X trading program, and any
section 126 sources that would be subject to a Federal NO_X
trading program.
The section 126 provisions require that any control remedy be
implemented within 3 years from the date of the finding that major
sources or a group of stationary sources emit or would emit in
violation of the relevant prohibition in section 110(a)(2)(D). Under
EPA's anticipated rulemaking schedule ⁴ on the petitions,
the compliance date for sources for which EPA makes such a finding
could be April 30, 2002; November 30, 2002; or May 1, 2003. Several
commenters expressed concern that the compliance deadline under section
126 was driving EPA's decision on the compliance deadline for the
NO_X SIP call. Therefore, they believed that no changes would
be made in the proposed NO_X SIP call deadline in response to
comments.
---------------------------------------------------------------------------

\4\ The eight northeastern States that filed section 126
petitions also filed suit in the District Court for the Southern
District of New York, to compel EPA to take action on those
petitions within prescribed periods. State of Connecticut v.
Browner, No. 98-1376 (S.D.N.Y., filed Feb. 25, 1998). The EPA and
the eight northeastern States jointly filed a motion to enter a
consent order prescribing certain dates for EPA action.
---------------------------------------------------------------------------

While EPA believes it is advantageous to coordinate the section 126
and NO_X SIP call actions, EPA disagrees that this constrains
EPA from being responsive to public comments and considering
alternative compliance dates. See discussion below in Section V,
NO_X Control Implementation and Budget Attainment Dates.
In the NO_X SIP call NPR, EPA proposed that States be
required to submit SIPs within 12 months of the final SIP call. One
commenter asserted that the timing and terms of the rulemaking schedule
for the section 126 petitions precludes EPA from considering public
comments advocating different SIP due dates for the NO_X SIP
call. The section 126 rulemaking schedule provides several options. One
option would allow findings on the petitions to be deferred pending
certain actions by the States and EPA on State submittals in response
to the NO_X SIP call. The premise for the specified schedule
is that the SIP due date would be September 30, 1999 (i.e., roughly 12
months from signature of the notice on the final NO_X SIP
call). As discussed below in Section VI, SIP Revision Criteria and
Schedule, EPA continues to believe 12 months is an appropriate
timeframe. However, had EPA determined that a longer timeframe for SIP
submittal was warranted, the section 126 rulemaking schedule would not
have restricted EPA from establishing a later due date.
One commenter supported the section 126 rulemaking schedule because
they thought it had the effect of using the SIP process rather than the
source-based petitions in that it provides an option of deferring
section 126 findings if EPA approves a State's NO_X SIP.
Another commenter thought that the conditions for deferring section 126
findings were too stringent, and, therefore, section 126 would
inevitably be triggered prior to approval of any SIP provisions. This
issue is discussed in detail in Section II.A.2.c. in the NPR EPA just
issued on the section 126 petitions, which appears in the docket.

E. OTAG

As discussed in the proposed SIP call, OTAG completed the most
comprehensive analyses of ozone transport ever conducted. The EPA
participated extensively in this process. The EPA believes that the
OTAG process was successful and generated much useful technical and
modeling information on regional ozone transport. This information
provided EPA with the foundation for this rulemaking.
The EPA received numerous comments regarding the relationship
between the OTAG recommendations and EPA's proposed SIP call. Some
commenters asserted that the Agency's proposal was inconsistent with
the OTAG recommendations, while others believed that EPA used the
information and recommendations from OTAG appropriately. Primarily,
commenters stated that OTAG recommended a range of controls for utility
sources instead of a uniform level of control for all of the included
States.
The OTAG did recommend consideration of a range of controls, and
although it did not specifically recommend uniform controls across a
broad region, such a control scheme is within the range of its
recommendation. The EPA's action today is based on its consideration of
OTAG's recommendations, as well as information resulting from EPA's
additional work, and extensive public input generated through notice-
and-comment rulemaking. The EPA continues to believe, for reasons
explained in Section III.F.1, Uniform vs. Regional Controls, that
requiring NO_X emissions reductions across the region in
amounts achievable by uniform controls is a reasonable, cost-effective
step to take at this time to mitigate ozone nonattainment in downwind
States for both the 1-hour and 8-hour standards.
Commenters also stated that EPA applied an electric utility control
level that was more stringent than the upper limit of the OTAG range of
utility controls. The OTAG recommended a range of utility controls that
falls between specific CAA-required controls and the less stringent of
85 percent reduction from the 1990 rate (lb/mmBtu), or 0.15 lb/mmBtu.
In determining the appropriate level of emissions reductions, EPA
considered what levels of NO_X reductions could be obtained
by applying, to various source sectors, controls that are among the
most cost effective and feasible with today's proven pollution control
technologies. The EPA chose emissions reductions that are equivalent to
an emission limit from utilities of 0.15 lb/mmBtu. The EPA acknowledges
that this level may be more protective than the most protective level
contained in the OTAG recommendation in some cases, but, as discussed
below in Section IV, Air Quality Assessment, EPA believes that it
provides the most improvement in air quality while staying within the
bounds of the most highly cost-effective technology available. (Cost
effectiveness is discussed in Section II.D.) In addition, by relying on
actual 1995-1996 continuous emission monitoring data, rather than
relying on estimated 1990 emission data, this approach provides a more
accurate way of determining the States' budgets since it minimizes any
chances of over-or under-estimation of emissions.
Commenters asserted that OTAG recommended 12 months for additional
modeling--especially subregional modeling--before promulgating the SIP
call; and these commenters expressed concern that EPA did not provide
this amount of time following publication of the NPR. As discussed in
more detail in Section I.F, Discussion of Comment Period and
Availability of Key

[[Page 57363]]

Information, the Agency ultimately provided approximately 1 year from
the conclusion of OTAG for States and other members of the public to
complete and submit subregional and other types of modeling. The EPA
has considered this additional modeling in finalizing today's rule.
Some commenters stated that the goal of OTAG was to address
attainment of the ozone NAAQS. This is incorrect. The OTAG's goal was
to reduce ozone transport, which is one of the steps necessary to
enable attainment; the goal was not to recommend an overall strategy
that would yield attainment through regional measures alone. The OTAG
articulated its overall goal as follows:

* * * identify and recommend a strategy to reduce transported
ozone and its precursors which, in combination with other measures,
will enable attainment and maintenance of the national ambient ozone
standard in the OTAG region. A number of criteria will be used to
select the strategy including, but not limited to, cost
effectiveness, feasibility, and impacts on ozone levels.⁵

\5\ Ozone Transport Assessment Group Policy Paper approved by
the Policy Group on December 4, 1995.

It is also EPA's goal to ensure that sufficient regional reductions
are achieved to mitigate ozone transport in the eastern half of the
United States and thus, in conjunction with local controls, enable
nonattainment areas to attain and maintain the ozone NAAQS.
Commenters indicated that OTAG focused only on the 1-hour standard
nonattainment problem and did not assess compliance implications of the
8-hour standard. For this reason, according to commenters, EPA should
not base today's action on the nonattainment of the 8-hour NAAQS. It is
true that OTAG was established to address transport issues associated
with meeting the 1-hour standard. The EPA did not promulgate the 8-hour
standard until shortly after OTAG concluded; thus, OTAG did not
recommend strategies to address the 8-hour NAAQS. However, because EPA
had proposed an 8-hour standard, OTAG did examine the impacts of
different strategies on 8-hour average ozone predictions.
In light of OTAG's work and additional information, EPA is able to
assess ozone transport as it relates to the 8-hour NAAQS and to set
forth requirements as necessary to address the 8-hour standard in this
rulemaking. Ozone transport causes problems for downwind areas under
either the 1-hour or 8-hour standard. The regional reductions of
NO_X that will be achieved through this SIP call for the 1-
hour NAAQS are key components for meeting the new 8-hour ozone standard
in a cost-effective manner. Therefore, EPA believes that the OTAG
recommendations for how to address ozone transport are valid for both
NAAQS.
Several commenters urged EPA to adopt and implement all Federal
measures identified in the OTAG recommendations.⁶ The Agency
is committed to continue implementing national control measures for
NO_X, as recommended by OTAG. In addition, EPA has adopted
the following national measures for purposes of reducing VOC:
architectural and industrial maintenance coatings, consumer/commercial
products, and autobody refinishing. The EPA has made no decisions
regarding further VOC reductions beyond the reductions specified as
phase I in the OTAG recommendations.⁷
---------------------------------------------------------------------------

\6\ The OTAG recommendations are located in Appendix B of the
November 7, 1997 NPR (62 FR 60376).
\7\ Letter to the Honorable Ken Calvert, Chairman, Subcommittee
on Energy and Environment, U.S. House of Representatives, from
Robert D. Brenner, Acting Deputy Assistant Administrator for Air and
Radiation, U.S. EPA, June 26, 1998, transmitting EPA's responses to
questions following the May 20, 1998 congressional hearing on EPA's
proposed rule on paints and coatings.
---------------------------------------------------------------------------

Other more specific comments concerning the OTAG recommendations
will be addressed throughout this rulemaking as the issues are discussed.

F. Discussion of Comment Period and Availability of Key Information

The EPA received numerous comments concerning the adequacy of the
comment period for the November 7, 1997 NPR and May 11, 1998 SNPR. Some
commenters remarked that the comment period for the NPR should be
extended to allow for development and review of technical information,
including inventory data, growth factors, and the resulting budget.
Commenters stated that the additional time was particularly necessary
for subregional air quality modeling, which is modeling designed to
isolate the impacts of emissions from a particular State or group of
States on downwind areas. Many specifically requested an additional 120
days, and one requested an additional 9 months. Some commenters
indicated that EPA did not incorporate their comments from the NPR into
the SNPR. Other commenters insisted that key information supporting the
rule is not publicly available. The EPA also received comments that
additional public hearings should be held in other locations of the
OTAG region.
1. Request for Extension of the Comment Period
The EPA allowed a 120-day public comment period for the November 7,
1997 NPR, which closed on March 9, 1998. By notice (63 FR 17349, April
9, 1998), EPA reopened the comment period for members of the public to
submit additional modeling analyses, as well as comments concerning the
implications that any additional modeling may have for the State NOx
budgets under consideration in the November 7, 1997 proposal. The
comment period was reopened through the end of the comment period on
the SNPR. The SNPR, which was published on May 11, 1998, allowed a
comment period until June 25, 1998. Thus, for most issues addressed in
the NPR, including air quality modeling issues, commenters received an
almost 8-month formal comment period. Indeed, many commenters had
access to the NPR immediately after October 10, 1997, when it was
signed and posted on an EPA website. The Agency also received a number
of comments after June 25, 1998, which were also reviewed and
considered in developing the final rule.
The EPA believes this additional opportunity for the public to
submit comments was reasonable. After March 9, 1998--the initial date
for close of the comment period on the NPR--EPA received numerous
comments on various issues raised in the NPR, including air quality
issues. Many of these comments were extensive, which indicates that
commenters received adequate time.
With respect to the concern that EPA did not incorporate comments
received on the NPR into the SNPR, it would not have been practical for
EPA to incorporate comments received on the NPR into the SNPR because
the SNPR was completed soon after the close of the comment period for
the NPR. In general, the SNPR addressed different aspects of the rule
than the NPR, and one of the purposes of the SNPR was to take comment
on several new issues, as noted above. The EPA has addressed comments
on both the NPR and SNPR in today's action.
The major issues raised in the comments are responded to throughout
the preamble of this final rule. A comprehensive summary of all
significant comments, along with EPA's response to the comments which
have not been responded to in the preamble (Response to Comments), can
be found in the docket for this rulemaking (Docket No. A-96-56).

[[Page 57364]]

2. Request for Time to Conduct Additional Modeling
The OTAG Policy Group, at its June 3, 1997 meeting, recommended
that States have the opportunity to conduct additional local and
subregional modeling and air quality analyses, as well as to develop
and propose appropriate levels and timing of controls. The EPA received
numerous comments related to OTAG's recommendation. The commenters
requested that the Agency give States more time to conduct this
additional modeling so that EPA could more accurately assess each
State's contribution to downwind nonattainment.
The EPA signed the NPR on October 10, 1997, and posted it on a
website at that time, although it was not published in the Federal
Register until November 7, 1997. As noted above, EPA reopened the
comment period through June 25, 1998 for submittal of additional air
quality modeling runs. In effect, this has extended the amount of time
for modeling analyses to over a year from the date OTAG submitted its
recommendations, and to over 8 months from the signature date for the
NPR. By the close of the comment period on June 25, 1998, EPA had
received numerous comments containing new and extensive air quality
modeling studies. Accordingly, EPA believes that commenters received
adequate time.
3. Availability of Key Information
A number of commenters asserted that EPA failed to make publicly
available key information, such as modeling and emissions inventory
data. Specifically, commenters stated that they did not have access to
the emissions data on which EPA based the air quality modeling for the
NPR. In addition, according to some commenters, several models used by
EPA and OTAG are proprietary models and have not been generally
available to the public.
In Section III.A.2, Availability, the Agency discusses the
availability of emissions inventory data to the public.
The OTAG and EPA conducted air quality modeling runs to determine
the level of contribution from emissions in upwind areas to ozone
nonattainment in downwind areas. Some of this modeling employed UAM-
V.⁸ The UAM-V has generally been available to the public for
the purpose of analyzing information relevant to today's rulemaking.
State and local agencies, as well as utility companies and other
stakeholders, have had access to licenses to use UAM-V.
---------------------------------------------------------------------------

\8\ Variable-Grid Urban Airshed Model.
---------------------------------------------------------------------------

Commenters objected that they were obliged either to purchase
licenses for use of the UAM-V model or to employ as a contractor the
model owner, and that these financial constraints restricted their
access to the model. Because this model has, in general, been privately
developed, EPA believes that reasonable fees for its use should be
expected. The EPA did not receive information indicating that the
associated expenses were other than reasonable. To the extent that
commenters experienced delays in obtaining the UAM-V model, EPA
believes that the extensions of the comment period resulted in adequate
time for comment. In any event, any commenter who was not able to gain
access in the timeframe desired was able to use a comparable model,
such as the Comprehensive Air Quality Model with Extensions (CAMx),
which is not proprietary. For the purpose of responding to public
comments, EPA is considering all information based on CAMx and similar
models.
The Agency made available additional modeling runs used to
determine emissions changes, costs and cost effectiveness for
electricity generating units (EGUs). These runs were placed on the IPM
Analyses web site at www.epa.gov/capi, with links to EPA's Office of
Air and Radiation Policy and Guidance web site.
On August 10, the EPA placed in the docket and made available on
the web site, modeling analyses and other information supporting
today's action. As noted above, by notice dated August 24, 1998 (63 FR
45032), EPA published a notice of availability which stated that
throughout the course of the rulemaking, EPA had placed information in
the docket or made it available on various web sites. This information
included inventory data and additional modeling runs. By placing those
materials in the docket and informing the public of their availability,
EPA provided 4-6 weeks for review and comment by the public. The EPA
did receive comments concerning this information from the Utility Air
Regulatory Group on September 9, and EPA is responding to those
comments in the Response To Comments document. The EPA notes that the
additional modeling analyses were performed in response to comments
received on the NPR urging EPA to conduct State-by-State modeling. The
Agency does not believe it is required to provide for additional
comment on every action it takes in response to comment, particularly
where, as here, the new information confirms the Agency's proposed
conclusions. Therefore, the Agency did not further extend the comment
period.
4. Public Hearings
The Agency conducted two hearings in Washington, DC, including a 2-
day hearing on February 3-4, 1998 for the NPR, and a 1-day hearing on
May 29, 1998 for the SNPR. Some commenters believe that additional
public hearings should have been held in other locations in the OTAG
region. The EPA believes these hearings provided reasonable opportunity
for oral comment on the proposed rulemaking given the timeframes
associated with this rulemaking. Therefore, the Agency did not schedule
any additional hearings. The public also had an opportunity to submit
written testimony within approximately 30 days after each hearing date.

G. Implementation of Revised Air Quality Standards

On July 18, 1997, EPA published its final rule for strengthening
the NAAQS for ozone by establishing an 8-hour standard (62 FR 38856).
Current monitoring data indicate that many areas in the East, Midwest
and South violate the 8-hour NAAQS. Along with areas violating the 1-
hour NAAQS, areas violating the 8-hour NAAQS are also affected by the
transport of ozone across the East. The regional NO_X
reduction strategy finalized in today's action will provide a mechanism
to achieve reductions that will assist States in attaining and
maintaining this revised standard. In fact, the regional reductions
alone should be enough to enable the vast majority of the new counties
violating the 8-hour NAAQS that are located in States throughout the
East to attain the revised 8-hour standard.\9\
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\9\ In the NPR (62 FR 60318, 60363), EPA provided estimates of
the number of counties expected to attain as a result of the
NO_X SIP call. The EPA will update this list in the coming
months. The updated estimates of which counties will attain will be
based on more current air quality data and on the State-by-State
emissions budgets contained in today's final rule.
---------------------------------------------------------------------------

On July 16, 1997, President Clinton issued a directive on the
implementation of the revised air quality standards. This
implementation policy was described in the NPR (62 FR 60318, 60362-64).
The EPA received numerous comments on this implementation policy and on
EPA's plan to create a transitional classification\10\ for 8-hour ozone
nonattainment areas that meet certain

[[Page 57365]]

criteria. Since these comments concern implementation efforts for the
revised 8-hour ozone standard and do not relate directly to the
NO_X SIP call on which EPA is taking final action in this
rulemaking, EPA is not responding in detail to the comments. The EPA
will address implementation of the revised standard separately. In
August 1998, EPA issued proposed guidance for public comment to explain
the implementation policy in further detail and to provide details on
SIP requirements for transitional areas (63 FR 45060, August 24, 1998).
The EPA expects to finalize the August 1998 draft guidance, as well as
guidance for areas other than transitional, by December 1998.\11\
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\10\ The ``transitional classification'' EPA intends for 8-hour
ozone nonattainment areas is further discussed in the NPR (62 FR
60318, 60363).
\11\ For a complete listing of the guidance and other actions
EPA plans to issue to implement the revised ozone and PM NAAQS, see
a table on EPA's implementation website: http://
ttnwww.rtpnc.epa.gov/implement/actions.htm.
---------------------------------------------------------------------------

H. Summary of Major Changes Between Proposals and Final Rule

This summary describes the major changes that have occurred since
the NPR and SNPR in each of the following sections of today's final
rule.
1. EPA's Analytical Approach (Section II.A)
. The NPR proposed two interpretations for the section
110(a)(2)(D)(i)(I) provisions concerning the ``significant
contribution'' test. Under the first, EPA would examine certain factors
relating to level of emissions and their ambient impact to determine
whether to make a finding that all of the emissions from a particular
State's sources contribute significantly to nonattainment or
maintenance problems downwind. If EPA made such a finding, then EPA
would examine certain cost factors to determine the extent to which the
SIP for the State must mitigate (reduce) its emissions. Under the
second interpretation, EPA would examine all of those factors
together--level of emissions, ambient impact, and costs--to determine
whether to make the finding with respect to a specified amount of
emissions. If EPA made the finding, then it would require the SIP to
eliminate that amount. In today's final rule, EPA is adopting the
second interpretation. The EPA indicates, however, that it would adopt
the same rule if it were instead implementing the first interpretation.
2. Cost Effectiveness of Emissions Reductions (Section II.D.)
. The methodology of determining cost effectiveness has not
changed. For all sources, the inventory and as a result, the source-
specific costs, in some cases, have changed. This results in a
different overall budget level and a different overall cost-
effectiveness value. For the non-EGUs, while the methodology has not
changed, the analysis focuses on large non-EGU sources. The methodology
in the NPR focused on all non-EGU sources.
3. Determination of Budgets (Section III.)
. For EGU, the EPA maintained the approach to use the
higher, by State, of 1995 or 1996 heat input data to calculate baseline
heat input rates for the NFR, and added 577 smaller units to the State
budget inventories which had erroneously been omitted from the NPR.
These units included electricity generating sources of 25 megawatts
(MW) or less of electrical output and additional units not affected
under the Acid Rain Program. Additional controls are not assumed for
these sources, but they are added to the budget at baseline levels. The
Agency has decided to use State-specific growth factors derived from
application of the IPM using the 1998 Base Case and chose to retain the
0.15 lbs/mmBtu as the assumed uniform control level for EGU budget
emissions determination.
. The EPA examined alternatives that focus on non-EGU point
source reductions from the largest source categories, and within each
of these categories assumed controls that would result in a regionwide
average cost effectiveness less than $2000/ton. The resulting budget
assumes the emissions reductions from large non-EGU sources that are
among the most cost effective to control and does not include
reductions from smaller sources and sources that, as a group, are not
quite as cost effective or efficient to control, or are already covered
by other Federal measures. As a result, this final rule assumes, for
purposes of calculating the State NO_X budgets, the following
emissions decreases from uncontrolled levels for the large (generally
greater than 250 mmBtu or 1 ton/day non-EGU sources (no emission
reductions are assumed for the smaller sources):

--Non-EGU boilers and turbines--60 percent decrease.
--Stationary internal combustion engines--90 percent decrease.
--Cement manufacturing plants--30 percent decrease.

It should be noted that point sources with capacities less than 250
mmBtu/hr but with emissions greater than 1 ton/day are not treated
differently from sources with capacities greater than 250 mmBtu/hr for
purposes of calculating the budget. This is a change from the NPR which
included RACT controls on units with capacities less than 250 mmBtu/hr
and emissions greater than 1 ton/day (see Section III.G.2.a). As under
the proposal, the rule allows States to choose control measures other
than the EPA-assumed controls to meet the numerical budgets.
. The EPA has implemented the following changes that the
Agency proposed in the NPR for calculating baseline NO_X
emissions from highway vehicles. A 1995 baseline is used for the final
rule in place of the 1990 baseline used in the NPR. The Highway
Performance and Monitoring System data were used to estimate States'
1995 vehicle miles traveled (VMT) by vehicle category, except in those
cases where EPA accepted revisions offered in the comments. Today's
action includes those mobile source reductions which EPA has determined
are appropriate to implement on a national basis, and which have been
promulgated in final form or are expected to be promulgated in final
form before States are required to comply with their budgets. The
highway vehicle budget components include the emission reductions
resulting from implementation of the National Low Emitting Vehicle
(NLEV) program, including the phase-in schedule agreed to by the
States, automobile manufacturers, and EPA. The highway budget
components do not include the effect of Tier 2 light-duty vehicle and
truck standards and any associated fuel standards since these standards
have not yet been proposed. The extent of the reformulated gasoline
(RFG) and inspection and maintenance (I/M) programs was not assumed to
change beyond that assumed for the NPR, except for those States that
were able to demonstrate that the NPR's modeling assumptions did not
conform to the State's SIP and did not reflect CAA requirements.
. The EPA has chosen to retain the 1990 baseline inventories
for nonroad mobile sources presented in the NPR for today's action,
with additional changes made in response to public comments. The
control strategies assumed for calculating the nonroad and stationary
area source budget components have not changed from the SNPR.
4. NO_X Control Implementation and Budget Achievement Dates
(Section V)
. The EPA proposed that the SIP revisions require full
implementation of the necessary State measures by September 2002 and
took comment on a range of dates from September 2002 through September
2004. Based on

[[Page 57366]]

public comments and feasibility analyses conducted by EPA, the Agency
is requiring an implementation date of May 1, 2003. The Agency is also
providing some compliance flexibility to States for the 2003 and 2004
ozone seasons by establishing State compliance supplement pools. This
is described in Section III.F.6.
5. SIP Criteria (Section VI.A)
. The Agency has determined that the additional SIP
approvability criteria, as proposed in the SNPR, should apply not only
when States choose to regulate EGUs (63 FR 25912), but also when States
choose to regulate large steam-producing units (i.e., combustion
turbines and combined cycle systems with a capacity greater than 250
mmBtu/hr).
. The Agency proposed revisions to part 51 requiring
continuous emissions monitoring systems (CEMS) on all large electrical
generating and steam-producing sources which States elect to subject to
emissions reduction requirements in response to this rulemaking. The
EPA took comment on requiring that, if a State chooses to regulate
these sources to meet the SIP call, the SIP must require these sources
to use the NO_X mass monitoring provisions of part 75,
subpart H, to demonstrate compliance with applicable emissions control
requirements. After considering comments, the Agency is requiring that,
in these circumstances, the SIP specify that large sources comply with
the monitoring provisions of part 75, subpart H, which includes non-
CEMS monitoring options for units that are infrequently operated or
units that have low mass emissions.
6. Emissions Reporting Requirements for States (Section VI.B)
. The proposed rule required that States report full-year,
as well as ozone-season, emissions from all sources for the triennial
inventories commencing with year 2002 emissions and the 2007 inventory,
and for those sources for which reports had to be submitted annually
starting with year 2003 emissions. The final rule requires only ozone-
season emissions reporting for all sources.
. In the SNPR, the EPA proposed, for purposes of reporting
requirements, to define a point source as a non-mobile source which has
NO_X emissions of 100 tons/year or greater. Under today's
action, States have the option of establishing a smaller emission
threshold than 100 tons/year of NO_X emissions in defining
point source. This will allow the definition of point source to remain
consistent with current definitions in local areas.
7. NO_X Budget Trading Program (Section VII.)
. For States that choose to participate in the
NO_X Budget Trading Program, the preamble clarifies the
intent of the model rule and identifies areas of the rule where States
have flexibility to include variations in their State rules.
. In the SNPR, the Agency solicited comment on a range of
options for incorporating banking into the trading program. After
considering these comments, the Agency is including banking provisions
in the final rule. The provisions allow for unlimited banking starting
in 2003 and includes a flow control mechanism to limit the emissions
variability associated with banking.
. One of the banking approaches presented in the SNPR
included the option for sources to generate and use early reduction
credits. Consistent with the provisions of the NO_X SIP call
which provide for State compliance supplement pools, the final rule
allows States to issue early reduction credits for certain
NO_X emissions reductions achieved between September 30, 1999
and May 1, 2003.
. The final rule clarifies the timing requirements for State
submission of allowance allocations to EPA and, as proposed, lays out
an allocation approach. Each State remains free to adopt the final
rule's allocation approach or adopt an allocation scheme of its own,
provided it meets the specified timing requirements, requires new
sources to hold allowances, and does not allocate more allowances than
are available in the State trading budget.
8. Interaction with Title IV NO_X Rule (Section VIII.)
. In the SNPR, EPA proposed revisions to part 76 addressing
the interaction between title IV and the NO_X SIP call. In
this final rule, EPA explains that the Agency is not adopting any of
the proposed revisions to part 76.
9. Administrative Requirements (Section X.)
. NPR Section VIII, Regulatory Analyses, has been replaced
in the final rule by Section X.A, Executive Order 12866: Regulatory
Impacts Analysis. The new final rule Section X.A indicates that EPA has
prepared a RIA for the final rule and cites the cost and benefit
estimates from that analysis.
. The final rule adds several Sections under X,
Administrative Requirements, that were absent from the NPR. These
include: Paperwork Reduction Act; Executive Order 13045: Protection of
Children from Environmental Health Risks and Safety Risks; Executive
Order 12898: Environmental Justice; Executive Order 12875: Enhancing
the Intergovernmental Partnerships; Executive Order 13084: Consultation
and Coordination with Indian Tribal Governments; Judicial Review; and
Congressional Review Act. These new Sections provide a more
comprehensive summary of the Acts and Executive Orders that could apply
to the final rule. Each Section identifies the requirements of the
relevant Act or Executive Order, indicates EPA's interpretation of
whether the Act or Executive Order actually applies to this rulemaking,
and, if so, indicates how the Agency has addressed the Act or Executive
Order.

II. EPA's Analytical Approach

A. Interpretation of the CAA's Transport Provisions

As indicated in the NPR, 62 FR 60323, the primary statutory basis
for today's action is the ``good neighbor'' provision of section
110(a)(2)(D)(i)(I), under which, in general, each SIP is required to
include provisions assuring that sources within the State do not emit
pollutants in amounts that significantly contribute to nonattainment or
maintenance problems downwind. This statutory requirement applies to
SIPs under both the 1-hour ozone NAAQS and the 8-hour ozone NAAQS.
1. Authority and Process for Requiring SIP Submissions Under the 1-Hour
Ozone NAAQS
a. Authority for Requiring SIP Submissions under the 1-Hour NAAQS.
Each State is currently required to have in place a SIP that implements
the 1-hour ozone NAAQS for areas to which that standard still applies.
In the NAAQS rulemaking, EPA determined that the 1-hour NAAQS would
cease to apply to areas that EPA determines have air quality in
attainment of that NAAQS (40 CFR 50.9(b)). In two recent rulemakings,
EPA identified numerous areas of the country to which the 1-hour NAAQS
no longer applies. ``Final Rule: Identification of Ozone Areas
Attaining the 1-Hour Standard and to Which the 1-Hour Standard is No
Longer Applicable,'' (63 FR 31014, June 5, 1998); ``Final Rule:
Identification of Additional Ozone Areas Attaining the 1-Hour Standard
and to Which the 1-Hour Standard is No Longer Applicable,'' (63 FR
27247, July 22, 1998).
The 1-hour NAAQS remains applicable to areas whose air quality
continues to monitor nonattainment. As noted above in Section I.B, General

[[Page 57367]]

Factual Background, these include many major urban areas in the eastern
half of the United States. States that contain these areas remain
responsible for meeting CAA requirements applicable to those areas for
the purpose of attaining the 1-hour NAAQS. For example, States are
responsible for attainment demonstrations for areas designated
nonattainment and classified as moderate or higher.
By the same token, States that are upwind of these areas are
responsible to meet the ``good neighbor'' requirements of section
110(a)(2)(D). This responsibility is not alleviated simply because, for
areas other than the current nonattainment areas, the 8-hour NAAQS has
replaced the 1-hour NAAQS.
b. Process for Requiring SIP Submissions under the 1-Hour NAAQS. As
explained in the NPR, the appropriate route for EPA to require SIP
submissions under section 110(a)(2)(D)(i)(I) with respect to the 1-hour
standard is issuance of a ``SIP call'' under section 110(k)(5).\12\
Section 110(k)(5) authorizes EPA to find that a SIP is substantially
inadequate to meet a CAA requirement and to require (``call for'') the
State to submit, within a specified period, a SIP revision to correct
the inadequacy. Specifically, section 110(k)(5) provides, in relevant part:
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\12\ As discussed in the NPR and in greater detail further
below, the basis for requiring a transport-related SIP revision for
the 8-hour standard is the requirement in section 110(a)(1) that
States submit SIPs meeting the requirements of section 110(a)(2)
within 3 years (or an earlier date established by EPA) of
promulgation of a new or revised NAAQS. This is discussed in further
detail below.

Whenever the Administrator finds that the applicable
implementation plan for any area is substantially inadequate to
attain or maintain the relevant [NAAQS], to mitigate adequately the
interstate pollutant transport described in section 176A or section
184, or to otherwise comply with any requirement of this Act, the
Administrator shall require the State to revise the plan as
necessary to correct such inadequacies. The Administrator shall
notify the State of the inadequacies, and may establish reasonable
deadlines (not to exceed 18 months after the date of such notice)
---------------------------------------------------------------------------
for the submission of such plan revisions.

By today's action, EPA is determining that the SIPs for the
specified jurisdictions are substantially inadequate to comply with the
requirements of section 110(a)(2)(D)(i)(I) because the relevant SIPs do
not contain adequate provisions prohibiting their sources from emitting
amounts of NO_X emissions that contribute significantly to
nonattainment in downwind areas that remain subject to the 1-hour
NAAQS. Based on these determinations, EPA is requiring the identified
States to submit SIP revisions containing adequate provisions to limit
emissions to the appropriate amount.
If a State does not submit the required SIP provisions in response
to this SIP call, EPA will issue a finding that the State failed to
make a required SIP submittal under section 179(a). This finding has
implications for sanctions as well as for EPA's promulgation of Federal
implementation plans (FIPs). Sanctions and FIPs are discussed in
Section VI, SIP Criteria and Emissions Reporting Requirements.
(1) Commenters' Arguments Concerning the Transport Provisions.
Commenters argued that EPA does not have unilateral authority to issue
a SIP call under section 110(k)(5) to require States to remedy SIPs
that do not meet the requirements of section 110(a)(2)(D). The
commenters noted that when Congress amended the CAA in 1990, Congress
provided that the sole authority for EPA and States to address
interstate transport of pollution is through transport commissions. In
support, the commenters state that Congress: (i) Added sections 176A
and 184, which authorize the establishment of transport regions and the
formation of transport commissions; (ii) revised section 110(k)(5) to
refer to those transport provisions; and (iii) revised section
110(a)(2)(D)(i) to require that SIP provisions designed to eliminate
interstate pollutant transport be consistent with other CAA
requirements. According to the commenters, these provisions, read as a
whole, mandate that if EPA believes that a transport problem exists,
EPA's sole recourse is to form a transport region under sections 176A
and/or 184; EPA may issue a SIP call to mandate compliance with section
110(a)(2)(D)(i) only in response to a recommendation of the transport
region. The commenters also claim that this scheme is sensible because
it provides a consensual forum for States to address interstate
pollution rather than allowing unilateral action on the part of EPA or
a State.
The EPA disagrees with the commenters' conclusion that these
statutory provisions make clear that EPA cannot require a State to
address interstate transport without first establishing a transport
commission and in the absence of a recommendation from the transport
commission. There is no language of limitation in sections 110(a)(2)(D)
or (k)(5), or 176A, or 184. Nor is there any support in the legislative
history for such a narrow reading of the statute. Moreover, under the
commenters' interpretation, the CAA Amendments of 1990 have placed
greater constraints on States' and EPA's ability to address the
interstate transport of pollution. Such an interpretation would be
inconsistent with the overall purpose of the CAA to ensure healthful
air. Thus, EPA believes that the transport provisions were added as an
additional tool to address interstate transport but were not intended
to preclude other methods of addressing interstate pollution than prior
to passage of the amendments.
Under the 1990 Amendments, Congress recognized the growing evidence
that ozone and its precursors can be transported over long distances
and that the control of transported ozone was a key to achieving
attainment of the ozone standard across the nation (Cong. Rec. S16903
(daily ed. Oct. 27, 1990) (statement of Sen. Mitchell); S16970
(conference report) S16986-87 (statement of Sen. Lieberman)). Thus, in
1990, Congress added a new mechanism to address interstate transport.
Specifically, Congress enacted sections 176A and 184, which provide a
mechanism for States to work together to address the interstate
transport problem. However, by their terms, these sections simply
provide authority for EPA to designate transport regions and establish
transport commissions. There is nothing in the language of these
provisions that indicates that they supersede the other statutory
mechanisms for addressing interstate transport, or that they now
provide the sole mechanism for resolving interstate pollution transport.
Moreover, although Congress expressly added these two provisions
through the 1990 Amendments, Congress did not in any way limit section
110(a)(2)(D), which requires States to address interstate transport in
their SIPs. The addition of the language providing that States' actions
under section 110(a)(2)(D) be ``consistent with [title I] of the Act''
cannot be read to limit the controls States may adopt to meet section
110(a)(2)(D) to those recommended by a transport
commission.¹³ After all, the transport region provisions are
only two of many provisions in title I. Rather, this

[[Page 57368]]

language concerning consistency should be read as clarifying that any
section 110(a)(2)(D) requirement must be consistent with other
provisions of title I. Similarly, this language makes explicit that SIP
revisions required in accordance with the procedures of the transport
provisions would meet the requirements of section 110(a)(2)(D)(i).
---------------------------------------------------------------------------

\13\ Taken to its logical conclusion, the commenters' argument
would mean that States are precluded from submitting a section
110(a)(2)(D) SIP unless it reflects measures recommended through the
transport commission process. The EPA does not believe that Congress
would first establish a specific mandate (to submit a SIP to address
interstate transport) and then limit it in such a cryptic fashion.
If Congress intended section 110(a)(2)(D) SIPs to only reflect
transport commission recommendations, Congress could have
specifically referenced sections 176A and 184 in section
110(a)(2)(D), rather than generally providing that SIPs be
``consistent'' with title I of the CAA.
---------------------------------------------------------------------------

Furthermore, it is significant that Congress did not in any sense
bind EPA's ultimate discretion to determine whether State plans
appropriately address interstate transport. Under sections 176A and
184, the States may only make recommendations to EPA. Thus, under the
transport provisions, as well as the general SIP requirements of
section 110(a)(2), EPA must ultimately decide whether the SIP meets the
applicable requirements of the CAA. If, as the commenters contend, EPA
is limited to calling on States to address interstate transport only by
strategies recommended by the State, then EPA would be precluded from
ensuring that States address interstate transport. For example, EPA
could establish a transport commission but the commission could fail to
make recommendations or make insufficient recommendations. (Section
176A provides that transport commissions may make recommendations to
EPA only by ``majority vote of all members'' other than those
representing EPA.) Such a reading of the statute would be absurd in
light of the growing recognition at the time of the 1990 Amendments
that transport is a real threat to the primary purpose of title I of
the CAA--attainment of the NAAQS.
By the same token, in amending section 110(k)(5) in the 1990
Amendments, Congress did not add anything that explicitly provides
that, in the case of interstate transport, section 110(k)(5) would
apply only when EPA approved (or substituted measures for) a transport
commission's recommendations. The reference in section 110(k)(5) to the
transport provisions of sections 176A and 184 does not preclude EPA's
use of the SIP call provision to call on States to ensure their SIPs
meet the requirements of section 110(a)(2)(D)(i). Section 110(k)(5)
also provides for EPA to call on States ``to otherwise comply with
requirements of this Act;'' among the requirements in chapter I of the
CAA is the requirement in section 110(a)(2)(D). The reference in
section 110(k)(5) to the transport provisions simply makes explicit
that EPA may employ section 110(k)(5) for the additional purpose of
requiring SIPs to include the control measures as recommended by
transport commissions and approved by EPA under the transport provisions.
Moreover, there is no indication in the legislative history of the
1990 Amendments that Congress intended the sections 176A and 184
transport provisions to supersede the section 110(k)(5) SIP call
mechanism for ensuring compliance with section 110(a)(2)(D)(i). Reading
the transport provisions to supersede the SIP call mechanism would
constitute a significant change from the CAA as it read prior to the
1990 Amendments. Even if the statute is ambiguous as to whether the
transport provisions supersede the SIP call mechanism--and EPA believes
the statute is clear that the transport provisions do not supersede--
congressional silence would suggest that Congress did not intend such a
significant change (See generally Harrison v. PPG Industries, Inc., 446
U.S. 578, 602, 100 S.Ct. 1889, 1902, 64 L.Ed.2d 525 (1980) (Rehnquist,
J., dissenting), cited with approval in Chisom v. Roemer, 501 U.S. 380,
396 n. 23, 111 S.Ct. 2354, 2364 n. 23, 115 L.Ed.2d 348 (1991)).
Finally, the commenter asserts that EPA's interpretation of the CAA
to allow a SIP call in the absence of a transport commission
recommendation reads out of the CAA the consensual transport commission
procedures under sections 176A and 184. This is simply not true. The
EPA interprets the transport commission process to be one tool to
assess and address interstate transport. In fact, the Northeast Ozone
Transport Commission, under section 184, has been active since
enactment of the 1990 Amendments. In 1995, EPA approved a
recommendation of that commission (60 FR 4712 ¹⁴). Transport
commissions remain a viable means for dealing with interstate
transport. Furthermore, contrary to the general implication of the
commenter's remark, the OTAG process, though not a formal transport
commission, provided an opportunity not only for Federal and State
governments to assess jointly the transport issue, but also involved
industry, environmental groups and others. The EPA based its SIP call
on information developed through OTAG, as well as additional analyses
performed by the Agency and information submitted by a variety of
groups during the comment period on the proposed rule. Thus, the OTAG
process contained consensual elements.
---------------------------------------------------------------------------

\14\ In Commonwealth of Virginia v. EPA, 108 F.3d 1397 (D.C.
Cir. 1997), the court vacated EPA's SIP call in response to the
Northeast Ozone Transport Commission's recommendation on the basis
that the EPA could not require States to adopt a specific control
measure under its section 110(k)(5) authority and that, in any
event, EPA could not require States to adopt stricter motor vehicle
emission standards under either section 110(k)(5) or section 184.
---------------------------------------------------------------------------

(2) Commenters' Arguments Concerning the Virginia case. Under one
of the approaches described in the proposed rule, EPA proposed to
determine, for each of various upwind States, the aggregate ``amounts''
of air pollutants (NO_X) that contribute significantly to
nonattainment, and that, therefore must be prohibited by the various
SIPs. The NO_X emissions budget for each State is an
expression of the amount of NO_X emissions that would remain
after the State prohibits the amount that contributes significantly to
downwind nonattainment. In the final rule issued today, EPA has
continued this approach, establishing emissions budgets for each of the
23 jurisdictions based on required reductions. This determination is an
important step toward assuring that overall air quality standards are
met downwind.
Commenters argue that even if EPA has authority to call on States
to address interstate transport, EPA does not have the authority under
section 110(a)(2)(D) to mandate that upwind States limit NO_X
emissions to specified amounts. Rather, according to this view, EPA's
authority is limited to determining that the upwind States' SIPs are
inadequate, and generally requiring the upwind States to submit SIP
revisions to correct the inadequacies. The upwind States would then,
according to this view, submit a SIP revision that implements what the
upwind States determine to be the appropriate amount of NO_X
reductions. If EPA believes that those amounts are too small to correct
the inadequacy, EPA could disapprove the SIP revisions.
Proponents of this view rely on the recent decision in Virginia v.
EPA, 108 F.3d 1397, 1406-10 (D.C. Cir. 1997) (Virginia) (citing Train
v. NRDC), in which the court vacated EPA's SIP call on the basis that
through it, EPA gave States no choice but to adopt the California low
emission vehicle (LEV) program. The court found that the language in
section 110(k)(5) that provides EPA with the authority to call on a
State to revise its SIP ``as necessary'' to correct a substantial
inadequacy did not change the longstanding precept that States have the
primary authority for determining the mix of control measures needed to
attain the NAAQS.
The EPA disagrees that the CAA prohibits EPA from establishing an
emissions budget through a SIP call requiring upwind States to prohibit
emissions that contribute significantly to downwind nonattainment.
Section

[[Page 57369]]

110(a)(2)(D) is silent regarding whether States or EPA are to determine
the level of emission reductions necessary to mitigate significant
contribution. The caselaw cited by the commenters only provides that
States are primarily responsible for determining the mix of control
measures--not the aggregate emission reduction levels that are
necessary. Moreover, Train v. NRDC, which underlies the Virginia
court's decision, relied on section 107(a) of the CAA, which specifies
only that each State is primarily responsible for determining a control
strategy to attain the NAAQS ``within such State.''
Section 110(a)(2)(D) does not provide who--EPA or the States--is to
determine the level of emission reductions necessary to address
interstate transport. As quoted above, section 110(a)(2)(D)(i)(I)
requires that SIPs contain ``adequate provisions prohibiting * * *
[sources] from emitting any air pollutant in amounts which will
contribute significantly to nonattainment'' downwind. Nor does this
provision indicate the criteria for determining the ``amounts'' of
pollutants that contribute significantly to nonattainment downwind. Nor
does this provision indicate the process for determining those
``amounts,'' including whether EPA or the States should carry out this
responsibility. ¹⁵ Under Chevron U.S.A., Inc. v. Natural
Resources Defense Council, 468 U.S. 1227, 105 S.Ct. 28, 82 L.Ed.2d 921
(1984) (Chevron), because the statute does not answer these specific
issues, EPA has discretion to provide a reasonable interpretation.
---------------------------------------------------------------------------

\15\ The EPA is not contending that the ``as necessary''
language in section 110(k)(5) provides the basis for EPA's authority
to identify the emissions budget for upwind States.
---------------------------------------------------------------------------

Neither the decision in Virginia, nor the body of caselaw upon
which it relies, addresses this issue. Rather, these cases address
solely the division between the States and EPA regarding the initial
identification of control measures necessary to attain the ambient air
quality standards. The issue before the court in Virginia was whether
EPA had offered States a choice in selecting control measures or
instead had mandated the adoption of a specific control measure.
Relying on Train v. NRDC, 421 U.S. 60, 95 S.Ct. 1470, 43 L.Ed.2d 731
1975), the Virginia court found that under title I of the CAA, EPA is
required to establish the overall air quality standards, but the States
are primarily responsible for determining the mix of control measures
needed to meet those standards and the sources that must implement
controls, as well as the applicable level of control for those sources.
The EPA must then review the State's determination only to the extent
of assuring that the overall air quality standards are met. If EPA
determines that the SIP's mix of control measures does not result in
achieving the overall air quality standards, EPA is required to
disapprove the SIP and promulgate a FIP, under which EPA selects the
sources for emissions reductions (Virginia, 108 F.3d at 1407-08, citing
Train v. NRDC, 421 U.S. 60, 95 S.Ct. 1470, 43 L.Ed.2d 731 (1975); Union
Electric Co. v. EPA, 427 U.S. 246, 96 S.Ct. 2518, 49 L.Ed.2d 474
(1976)). This line of cases, which focuses on the selection of
controls, does not address whether EPA or the States--in the first
instance--should determine the aggregate amount of reductions necessary
to address interstate transport.
Moreover, NRDC v. Train addresses State plans for purposes of
intrastate emissions planning. In determining that States have the
primary authority for determining the control measures needed to attain
the standard, the court relied on section 107(a) of the CAA, which
provided (and still provides) that:

Each State shall have the primary responsibility for assuring
air quality within the entire geographic area comprising such State
by submitting an implementation plan which will specify the manner
in which national primary and secondary ambient air quality
standards will be achieved and maintained within each air quality
region in such State.''

(421 U.S. at 64, 95 S.Ct at 1474-75 (emphasis added)).

Thus, the underlying support for the court's determination in Train
v. NRDC applies only where a State is determining the mix of controls
within its boundaries, not to the broader task of determining the
aggregate emissions reductions needed in conjunction with emissions
reductions from a number of other States in order to address the impact
of transported pollution on downwind States. ¹⁶
---------------------------------------------------------------------------

\16\ The court's decision in Train v. NRDC appears to rely on
the plain language of the statute in holding that a State is
primarily responsible for determining the mix of control measures
necessary to demonstrate attainment within that State's borders. The
court in Virginia appears to adopt this ``plain meaning''
interpretation without addressing that the language in section
107(a) applies only to intrastate issues. This issue is not relevant
in the present case, however, since States are free to decide the
mix of control measures under today's final action.
---------------------------------------------------------------------------

Although the cases to date have not addressed directly whether it
is the province of EPA or the States to determine the aggregate amounts
of emissions to be prohibited (and hence, the amounts that may remain--
i.e., the emissions budgets), EPA believes it reasonable to interpret
the ambiguity in section 110(a)(2)(D)(i)(I) to include this
determination among EPA's responsibilities, particularly in the current
circumstances. Determining the overall level of air pollutants allowed
to be emitted in a State is comparable to determining overall standards
of air quality, which the courts have recognized as EPA's
responsibility, and is distinguishable from determining the particular
mix of controls among individual sources to attain those standards,
which the caselaw identifies as a State responsibility. In Train, a
State was required to assure that its own air quality attained overall
air quality standards and to implement emissions controls to do so.
Under these circumstances, the court clarified that while the
responsibility for determining the overall air quality standards was
EPA's, the responsibility for determining the specific mix of controls
designed to achieve that air quality was the State's. By comparison, as
stated earlier, a transport case, under section 110(a)(2)(D)(i), does
not concern any requirement of the upwind State to assure that its own
air quality attains overall air quality standards. Rather, a transport
case concerns the upwind State's requirement to assure that its
emissions are reduced to a level that will not contribute significantly
to nonattainment downwind. Determining this overall level of reductions
for the upwind State is analogous to determining overall air quality
standards, and, thus, should be the responsibility of EPA.
Once EPA determines the overall level of reductions (by assigning
the aggregate amounts of emissions that must be eliminated to meet the
requirements of section 110(a)(2)(D)), it falls to the State to
determine the appropriate mix of controls to achieve those reductions.
Unlike the regulation at issue in Virginia, today's regulation
establishing emission budgets for the States does not limit the States
to one set of emission controls. Rather, the States will have
significant discretion to choose the appropriate mix of controls to
meet the emissions budget. The EPA has based the aggregate amounts to
be prohibited on the availability of a subset of cost-effective
controls that are among the most cost effective available. As explained
elsewhere in this final rule and the NPR, the State may choose from a
broader menu of cost-effective, reasonable alternatives, including some
(e.g., vehicle inspection and maintenance programs and reformulated

[[Page 57370]]

gasoline) that may even be more advantageous in light of local concerns.
The task of determining the reductions necessary to meet section
110(a)(2)(D) involves allocating the use of the downwind States' air
basin. This area is a commons in the sense that the contributing State
or States have a greater interest in protecting their local interests
than in protecting an area in a downwind State over which they do not
have jurisdiction and for which they are not politically accountable.
Thus, in general, it is reasonable to assume that EPA may be in a
better position to determine the appropriate goal, or budget, for the
contributing States, while leaving to the contributing States'
discretion to determine the mix of controls to make the necessary
reductions.
The EPA's decision to assign the budgets in the final rule is
particularly reasonable. Today's rulemaking involves almost half the
States in the Nation, and although these States participated in OTAG
beginning more than 3 years ago, they still have not agreed on whether
particular upwind States should be treated as having sources whose
emissions contribute significantly to downwind nonattainment, what the
aggregate level of emissions reductions should be, or what the State-
by-State reductions should be. The sharply divergent positions taken by
the States in their comments on the NPR and SNPR raise doubts that
those disagreements could ever be resolved by consensus. It is most
efficient--indeed necessary--for the Federal government to establish
the overall emissions levels for the various States. This is
particularly true for an interstate pollution problem such as the one
being dealt with in this action where the downwind areas at issue are
affected by pollution coming from several States and the actions taken
by each of the concerned States could have an effect on the appropriate
action to be taken by another State. For example, if EPA did not
specify the emissions to be prohibited from each of the various States
affecting New York City, each of those States might claim it could
reduce its emissions less provided other States did more. Or, a State
close to New York might assert that it could just as effectively deal
with its contribution to New York through additional VOC, rather than
NO_X, reductions and submit a section 110(a)(2)(D) SIP based
on a VOC-control rather than NO_X-control strategy. These
choices, however, even assuming they were valid, necessarily relate to
the choices that would need to be made by the other upwind States
(e.g., Pennsylvania's choice of a VOC-dominated 110(a)(2)(D) control
strategy to deal with its contribution to New York could affect what
Ohio or New Jersey would need to do to deal with their own
contributions by lowering the overall level of NO_X
reductions being obtained throughout the pertinent region). Where many
States are involved and the choices of each individual State could
affect the choices and decisions of the other States the need for
initial federal action is manifest. The EPA's action to determine the
amount of NO_X emissions that each of the States must
prohibit in this widespread geographic area is needed to enable the
States to decide expeditiously how to achieve those reductions in an
efficient manner that will not undermine the actions of another State.
By notifying each State in advance of its reduction requirements, EPA
enables each State to develop its plan with full knowledge of the
amount and kind of reductions that must be achieved both by itself and
other affected States. The EPA's action provides the minimum framework
necessary for a multi-state solution to a multi-state problem while
preserving the maximum amount of state flexibility in terms of the
specific control measures to be adopted to achieve the needed emission
reductions. The reasonableness of EPA's approach to the interstate
ozone transport problem was recently recognized by a US Court of
Appeals in the context of upholding EPA's redesignation of the
Cleveland ozone nonattainment area to attainment in light of EPA's
approach to the regional transport problem. In the course of doing so
the court rejected the contention that a separate analysis of the
current adequacy of the Cleveland SIP under section 110(a)(2)(D) was
required as a prerequisite to redesignation. The court, after
describing the November 7, 1997 proposed SIP call and the path EPA was
on to deal with this multi-state regional problem, upheld EPA's
redesignation and stated that ``[w]e find that the EPA's approach to
the regional transport problem is reasonable and not arbitrary or
capricious.'' Southwestern Pennsylvania Growth Alliance v. Browner, 144
F.3d 984, 990 (6th Cir. 1998).
As noted above, commenters have argued that if EPA determines to
issue any SIP call, the SIP call must be more general (i.e., one that
simply requires revised SIPs from upwind areas) and not specify the
amounts of NO_X emissions that those areas must prohibit.
However, if EPA issued a general SIP call and an upwind State responded
by submitting an inadequate SIP revision, EPA would disapprove that
SIP, and in the disapproval rulemaking, EPA would be obliged to justify
why the submitted SIP was unacceptable. Without determining an
acceptable level of NO_X reductions, the upwind State would
not have guidance as to what is an acceptable submission. The EPA's
determination, as part of the issuance of the SIP call, of the amounts
of NO_X emissions the SIPs must prohibit obviously provides
for more efficient and smooth-running administrative processes at both
the State and Federal levels. For the same reasons that EPA believes it
is appropriate for the Agency to establish the emissions budgets under
the authority of section 110(a)(2)(D) and (k)(5), EPA believes that it
is necessary to do so through a rule under the general rulemaking
authority of section 301(a). Setting such a rule is necessary, as a
practical matter, for the Administrator's effective implementation of
section 110(a)(2)(D). See NRDC v. EPA, 22 F.3d 1125, 1146-48. Without
such a rule the States could be expected to submit SIPs reflecting
their conflicting interests, which could result in up to 23 separate
SIP disapproval rulemakings in which EPA would need to define the
requirements that each of those States would need to meet in their
later, corrective SIPs. That in turn would trigger a new round of SIP
rulemakings to judge those corrective SIPs. The delay attendant to that
process would thwart timely attainment of the ozone standards.
2. Authority and Process for Requiring SIP Submissions under the 8-Hour
Ozone NAAQS
a. Authority for Requiring SIP Submissions under the 8-Hour NAAQS.
(1) SIP Submissions Under CAA Section 110(a)(1). In the NPR and SNPR,
EPA proposed to require the 23 upwind jurisdictions to submit SIP
revisions to reduce emissions that exacerbate ozone problems in
downwind States under the 8-hour ozone NAAQS, as well as the 1-hour
NAAQS. The EPA recognized that under the 8-hour NAAQS, areas have not
yet been designated as attainment, nonattainment, or unclassifiable,
and are not yet required to have SIPs in place. Even so, EPA proposed
that upwind areas be required to submit SIPs meeting the requirements
of section 110(a)(2)(D)(i)(I) with respect to the 8-hour NAAQS.
In today's action, EPA is confirming its view that it has authority
under the 8-hour NAAQS to require SIP submittals under section
110(a)(2)(D)(i)(I) to reduce NO_X emissions by the prescribed
amounts. Section 110(a)(1) provides, in relevant part--

[[Page 57371]]

Each State shall * * * adopt and submit to the Administrator,
within 3 years (or such shorter period as the Administrator may
prescribe) after the promulgation of a national primary ambient air
quality standard (or any revision thereof) * * * a plan which
provides for implementation, maintenance, and enforcement of such
primary standard in each (area) within such State.

Section 110(a)(2) provides, in relevant part--
Each implementation plan submitted by a State under this Act
shall be adopted by the State after reasonable notice and public
hearing. Each such plan shall [meet certain requirements, including
those found in section 110(a)(2)(D)].

The provisions of section 110(a)(1) and (a)(2) apply by their terms
to all areas, regardless of whether they have been designated as
attainment, nonattainment, or unclassifiable under section 107. The
plain meaning of these provisions, read together, is that SIP revisions
are required under the revised NAAQS within 3 years of the date of
revision, or earlier if EPA so requires, and that those SIP revisions
must meet the requirements of section 110(a)(2), including subparagraph
(D).
That the SIP submission requirements of section 110(a)(1) are
triggered by the promulgation of a new or revised NAAQS is made even
clearer by comparing section 172(b), which applies by its terms only to
areas that have been designated nonattainment under section 107.
Section 172(b) provides, in relevant part--

At the time the Administrator promulgates the designation of any
area as nonattainment with respect to a [NAAQS] under section 107(d)
* * *, the Administrator shall establish a schedule according to
which the State containing such area shall submit a plan or plan
revision * * * meeting the applicable requirements of subsection (c)
of this section and section 110(a)(2) * * * Such schedule shall at a
minimum, include a date or dates, extending no later than 3 years
from the date of the nonattainment designation, for the submission
of a plan or plan revision * * * meeting the applicable requirements
of subsection (c) of this section and section 110(a)(2) * * *

Section 172(b) establishes the schedule for submissions due with
respect to nonattainment areas under sections 172(c) and 110(a)(2). The
section 172(c) requirements apply only with respect to areas designated
nonattainment.¹⁷
---------------------------------------------------------------------------

\17\ As quoted above, section 172(b) refers to ``applicable
requirements of * * * section 110(a)(2).'' This reference appears to
mean those requirements of section 110(a)(2) that either (i) relate
to all SIP submissions, such as the requirement for reasonable
notice and public hearing in the language at the beginning of
section 110(a)(2); or (ii) relate particularly to SIP submissions
required for nonattainment areas, but that have not yet been
submitted by the State.
---------------------------------------------------------------------------

In the NPR, EPA proposed that section 110(a)(1) mandates SIP
submissions meeting the requirements of section 110(a)(2)(D) and
provides full authority for EPA to establish a submission date within 3
years of the July 18, 1997 8-hour ozone NAAQS promulgation date (62 FR
38856 (NAAQS rulemaking): 62 FR 60325 (NOx SIP call NPR)). The EPA
further asserted in the NPR that EPA has the authority to establish
different submittal schedules for different parts of the section
110(a)(1) SIP revision, and that EPA may require the section
110(a)(2)(D) submittal first so that upwind reductions may be secured
at an earlier stage in the regional SIP planning process (62 FR 60325).
Subsections (ii) and (iii) of this section further elaborates on the
reasoning underlying EPA's decision to retain its proposal to require
SIP submissions under section 110(a)(2)(D) for the 8-hour standard.
(2) Commenters and the Definition of ``Nonattainment.'' Commenters
challenged several aspects of EPA's proposal to evaluate the
contribution of upwind areas under the 8-hour NAAQS. Commenters
asserted that section 110(a)(2)(D)(i) applies to constrain emissions
from upwind sources only with respect to downwind areas that are
designated nonattainment. According to these commenters, until EPA
designates areas nonattainment under the 8-hour NAAQS, EPA has no
authority to require SIP submissions, under section 110(a)(1), from
upwind areas with respect to the 8-hour NAAQS. One commenter pointed
out that the new source review requirements and ozone nonattainment
requirements enacted in the 1990 Amendments apply only to areas
designated nonattainment.
The EPA disagrees with this comment. Section 110(a)(2)(D)(i)(I)
provides that a SIP must prohibit emissions that ``contribute
significantly to nonattainment in * * * any other State.''
¹⁸ The provision does not, by its terms, indicate that this
downwind ``nonattainment'' must already have been designated under
section 107 as a nonattainment ``area.'' If the provision were to
employ the term ``area'' in conjunction with the term
``nonattainment,'' then it would have to be interpreted to apply only
to areas designated nonattainment. Other provisions of the CAA do
employ the term ``area'' in conjunction with ``nonattainment,'' and
these provisions clearly refer to areas designated nonattainment (e.g.,
sections 107(d)(1)(A)(i), 181(b)(2)(A), 211(k)(10)(D)). Similarly, the
provisions to which the commenter appeared to refer--section 172(b)/
172(c)(5) (new source review) and section 181(a)(1)/182 (classified
ozone nonattainment area requirements)--by their terms apply to a
nonattainment ``area.'' In contrast, section 110(a)(2)(D) refers to
only ``nonattainment,'' not to a nonattainment ``area.''
---------------------------------------------------------------------------

\18\ Section 110(a)(2)(D)(i)(I) further provides that a SIP must
prohibit emissions that ``interfere with maintenance by * * * any
other State.''
---------------------------------------------------------------------------

By the same token, section 176A(a) authorizes EPA to establish a
transport region whenever ``the Administrator has reason to believe
that the interstate transport of air pollutants from one or more States
contributes significantly to a violation of a [NAAQS] in one or more
other States.'' This reference to ``a violation of a [NAAQS]'' makes
clear that EPA is authorized to form a transport region when an upwind
State contributes significantly to a downwind area with nonattainment
air quality, regardless of whether the downwind area is designated
nonattainment. The EPA believes that section 110(a)(2)(D) should be
read the same way in light of the parallels between section
110(a)(2)(D) and section 176A(a). Both provisions address transport and
both are triggered when emissions from an upwind area ``contribute
significantly'' downwind. It seems reasonable to apply a consistent
approach to the type of affected downwind area, which would mean
interpreting the term ``nonattainment'' in section 110(a)(2)(D) as
synonymous with the phrase ``a violation of a [NAAQS]'' in section
176A(a). The CAA contains other provisions, as well, that refer to the
factual, air quality status of a particular area as opposed to its
designation status. These provisions include, among others, (i)
sections 172(c)(2) and 171(1), the reasonable further progress
requirement, which requires nonattainment SIPs to provide for ``such
annual incremental reductions in emissions * * * as * * * may * * * be
required * * * for the purpose of ensuring attainment of the [NAAQS]''
(emphasis added); and (ii) section 182(c)(2), the attainment
demonstration requirement, which mandates a ``demonstration that the
[SIP] * * * will provide for attainment of the [NAAQS]'' (emphasis
added). The emphasized terms clearly refer to air quality status. In a
series of notices in the Federal Register, EPA relied on these
references to air quality status in determining that areas seeking to
redesignate from nonattainment to attainment did not need to complete
ROP SIPs or attainment demonstrations--even though those requirements
generally applied to areas

[[Page 57372]]

designated nonattainment--as long as the air quality for those
redesignating areas was, in fact, in attainment. See ``State
Implementation Plans; General Preamble for the Implementation of Title
I of the Clean Air Act Amendments of 1990; Proposed Rule,'' 57 FR
13498, 13564 (April 16, 1992); ``Determination of Attainment of Ozone
Standard for Salt Lake and Davis Counties, Utah, and Determination
Regarding Applicability of Certain Reasonable Further Progress and
Attainment Demonstration Requirements: Direct Final Rule,'' 60 FR
30189, 30190 (June 8, 1995); and ``Determination of Attainment of Ozone
Standard for Salt Lake and Davis Counties, Utah, and Determination
Regarding Applicability of Certain Reasonable Further Progress and
Attainment Demonstration Requirements: Final Rule,'' 60 FR 36723, 36724
(July 18, 1995). The EPA's interpretation was upheld by the Court of
Appeals for the 10th Circuit, in Sierra Club v. EPA, 99 F.3d 1551, 1557
(10th Cir. 1996).
Accordingly, EPA believes it clear that the reference in section
110(a)(2)(D)(i)(I) to ``nonattainment'' refers to air quality, not
designation status. The EPA believes this matter is clearly resolved by
reference to the terms of the provision itself, so that under the first
step of the Chevron analysis, no further inquiry is needed. If,
however, it were concluded that the provision is ambiguous on this
point, then EPA believes that, under the second step in the Chevron
analysis, EPA should be given deference for any reasonable
interpretation. Interpreting ``nonattainment'' to refer to air quality
is reasonable for the reasons described above.¹⁹
---------------------------------------------------------------------------

\19\ Similarly, EPA believes that the term ``maintenance'' in
another clause of section 110(a)(2)(D)(i)(I) refers to air quality
status as well. This clause includes only the term ``maintenance,''
and does not include the term ``area.''
---------------------------------------------------------------------------

The structure of the schedules for requiring SIP submissions and
designating areas nonattainment provides support for EPA's
interpretation. As noted above, section 110(a)(1) requires States to
submit SIPs covering all their areas--regardless of whether designated,
or how designated-- within 3 years of a NAAQS revision and requires
that those SIPs include provisions meeting the requirements of section
110(a)(2)(D).²⁰ When a new or revised NAAQS is promulgated,
section 107(d)(1) authorizes a process of up to 3 years for
designations. States must recommend designations within one year of
promulgation of a new or revised NAAQS and EPA must designate areas
within 2 years of promulgation; EPA may take up to 3 years to designate
areas if insufficient information prevents designations within 2 years.
In the case of the 8-hour ozone NAAQS, Congress provided specific
legislation for designations (Pub. L. 105-178 Sec. 6103). Under this
new legislation, States are provided 2 years to make recommendations
and EPA must designate areas within 1 year of the time State
recommendations are due. Because of this legislation, designations must
occur 3 years following promulgation of the NAAQS (July 2000). The EPA
believes that it is not sensible to interpret the term
``nonattainment'' in section 110(a)(2)(D)(i)(I) to refer to
nonattainment designations because those designations may not be made
until 3 years after the promulgation of a new or revised NAAQS, and the
section 110(a)(2)(D) submittals are due within 3 years.
---------------------------------------------------------------------------

\20\ See ``Re-issue of the Early Planning Guidance for the
Revised Ozone and Particulate Matter (PM) National Ambient Air
Quality Standards (NAAQS),'' memorandum from Sally L. Shaver, dated
June 16, 1998.
---------------------------------------------------------------------------

Further, interpreting the reference to ``nonattainment'' as a
reference to air quality, and not designation, is consistent with the
air quality goals of section 110(a)(2)(D) and the CAA as a whole. In
the present case, it is clear from air quality monitoring and modeling
that large areas of the eastern part of the United States are in
violation of the 8-hour NAAQS, and it is also clear from air quality
modeling studies that NO_X emissions from sources in upwind
States contribute to those air quality violations. The EPA currently
has available all the information that it needs to determine whether
upwind States should be required to revise their SIPs to implement
appropriate reductions in NO_X emissions. The designation
process will clarify the precise boundaries of the downwind areas, but
because ozone is a regional phenomenon, information as to the precise
boundaries of the downwind areas is not necessary to implement the
requirements of section 110(a)(2)(D)(i). As a result, no air quality
purpose will be served by waiting until the downwind areas are
designated nonattainment.
On the contrary, taking action now is necessary to protect public
health. As described in Section I.G., the regional NO_X
reductions required under today's action will allow numerous areas
currently in violation of the 8-hour NAAQS to attain that standard. For
the millions of people living in those areas, today's action will
advance the date by which these areas will meet the revised ozone
standard. Taking action now is particularly important because one of
the sub-population groups at higher risk to ozone health effects is
children who are active and spend more time outdoors during the summer
months when ozone levels are elevated.
(3) EPA's Authority to Require Section 110(a)(2)(D) Submissions in
Accordance with section 110(a)(1). Commenters argue that sections
110(a)(1), (a)(2), and 172(b) should be read so that only requirements
under section 110(a)(2) that are unrelated to nonattainment are due
under the section 110(a)(1) timetable. These commenters contend that
requirements under section 110(a)(2) that are related to
nonattainment--including section 110(a)(2)(D)--are due under the
section 172(b) timetable, that is, within 3 years of the designation of
areas as nonattainment. In support, these commenters rely on language
in section 110(a)(1) indicating that the submissions are for plans for
air quality regions ``within such State.'' Finally, certain commenters
cite as further support for their position the definition of the term
``nonattainment'' as found in section 107(d)(1)(A), claiming that the
definition includes interstate transport areas.
As noted above, section 110(a)(1) provides that States must submit
SIP revisions providing ``for the implementation, maintenance and
enforcement'' of the NAAQS in each area of the State within 3 years (or
a shorter time prescribed by the Administrator) following promulgation
of a new or revised NAAQS. Section 110(a)(2) then sets forth the
applicable elements of a SIP. These provisions apply to all areas
within the State, regardless of designation. Section 172(b) establishes
a SIP submission schedule for nonattainment areas. It provides that at
the time EPA designates areas as nonattainment, EPA shall establish a
SIP submission schedule for the submission of a SIP meeting the
requirements of section 172(c).
While EPA agrees that there is overlap between the submission
requirements under sections 110(a)(1)-(2) and 172(c), EPA believes that
the plain language of section 110(a)(1)-(2) authorizes EPA to require
the section 110(a)(2)(D) SIPs on the schedule described today, and that
there is nothing to the contrary in section 172. Sections 110(a)(2) and
172 contain cross-references to each other.²¹

[[Page 57373]]

These cross-references indicate that under certain circumstances, the
section 110(a)(2)(D) submittal may be required under section 110(a)(1);
and under other circumstances, the section 110(a)(2)(D) submittal may
be required under section 172(b). These cross-references are
particularly relevant with respect to nonattainment areas, which are
subject to both sections 110(a) (1) and (2) and 172. In the current
situation, EPA believes that it is appropriate to require the
submissions to meet section 110(a)(2)(D) in accordance with the
schedule in section 110(a)(1) rather than under the schedule for
nonattainment areas in section 172(b).²²
---------------------------------------------------------------------------

\21\ Section 110(a)(2)(D) provides that areas designated
nonattainment must submit SIPs in accordance with ``part D'' (which
includes section 172). Section 172(b) requires EPA to establish a
schedule for designated nonattainment areas to meet the requirements
of sections 172(c) and 110(a)(2); section 172(c)(7) requires that
nonattainment SIPs shall meet the requirements of section 110(a)(2).
\22\ In other situations, EPA has indicated that certain
elements of section 110(a)(2) would be better addressed in
accordance with the timeframe established in section 172. See e.g.,
60 FR 12492, 12505 (March 7, 1995) Proposed Requirements for
Implementation Plans and Ambient Air Quality Surveillance for Sulfur
Oxides (Sulfur Dioxide) National Ambient Air Quality Standard.
---------------------------------------------------------------------------

The EPA has provided that, for the revised ozone and particulate
matter NAAQS, States must assess their section 110 SIPs by July 18,
2000 to ensure that they adequately provide for implementing the
revised standards. See Re-issue of the Early Planning Guidance for the
Revised Ozone and Particulate Matter (PM) National Ambient Air Quality
Standards (NAAQS), memorandum from Sally L. Shaver, dated June 16,
1998. The EPA recognized that the section 110 SIP should generally be
sufficient to address the revised NAAQS. However, the Agency noted
three areas that the States particularly needed to assess, including
whether the SIP adequately addressed section 110(a)(2)(D). The EPA also
provided that the States should submit revisions to address section
110(a)(2)(D) on the timeframe established by the final NO_X
SIP call, when issued. The submittal date that EPA has specified in the
final NO_X SIP call rule is consistent with both the Early
Planning Guidance and with section 110(a)(1) and (2) of the CAA.
The EPA acknowledges that it has not historically required an
affirmative submission under section 110(a)(2)(D), applicable to
specific sources of emissions, in response to the promulgation of a new
or revised NAAQS. In part, this is because sufficient technical
information was not available to determine which sources ``contribute
significantly'' to nonattainment in a downwind area. In the absence of
such a determination, States were unable to regulate sources under this
provision in any meaningful way. However, based on the many analyses
performed over the last several years, EPA believes that there is now
affirmative information regarding significant contribution to ozone
violations in the eastern portion of the country; in light of that
evidence, it would not be appropriate to defer action under section
110(a)(2)(D) until a later time.
Moreover, as noted above, the section 172(c) SIP submissions apply
only to areas designated nonattainment. Specifically, section 172(b)
provides that ``[a]t the time'' EPA designates an area as
nonattainment, EPA shall set a schedule ``according to which the State
containing such area shall submit'' SIPs. Section 171(2) provides
further clarification by providing that for purposes of part D of title
I of the CAA (CAA sections 171-193) ``[t]he term `nonattainment area'
means, for any air pollutant, an area which is designated
`nonattainment' with respect to that pollutant within the meaning of
section 107(d).'' By its terms then, section 172 does not apply to
areas designated attainment or unclassifiable (even if such areas are
not attaining the standard) or for areas not yet designated. Thus,
section 110(a)(1) provides the only submission schedule for areas not
designated nonattainment. For those areas, the commenters' argument
that section 172(b) should establish the timetable for section
110(a)(2)(D)(i) SIPs clearly fails. Since certain portions of the 23
jurisdictions covered by this rule likely will not be designated
nonattainment for the 8-hour standard, EPA believes that the section
110(a)(1) schedule is the only schedule (and thus is the reasonable
schedule) to follow for purposes of the SIP call.
Furthermore, contrary to the commenters' assertions, the definition
of nonattainment does not broadly include areas that contribute to
nonattainment in a downwind State. The definition of nonattainment
includes areas that have monitored violations of the standard and areas
that ``contribute to ambient air quality in a nearby area'' that is
violating the standard (section 107(d)(1)(A)(i) (emphasis added)).
Thus, only ``nearby'' areas that contribute to violations of a standard
will be included in the nonattainment designation; areas contributing
to longer-range transport will not be designated nonattainment based
solely on that longer-range transport. Therefore, they will not be
subject to section 172(c) requirements and timing.
The commenters argue that EPA's position that section 110(a)(1)
governs the section 110(a)(2)(D) SIP submittal schedule leads to the
absurd result that upwind areas will be required to submit SIPs dealing
with their contribution to a nonattainment problem downwind before the
downwind area will be required to submit SIPs under section 172(b). The
commenters explain that section 110(a)(2) requires SIP submittals on a
faster timetable (within 3 years from the date of promulgation or
revision of a NAAQS) than section 172(b) (within 3 years from the date
of designation as nonattainment). The commenters also contend that
section 107 provides that States have the primary responsibility for
ensuring attainment within their boundaries; only after a State
implements all statutorily required and necessary measures can it
pursue reductions in other areas through a SIP call or section 126. The
commenters contend that the SIP call is contrary to the plain language
of section 107 and congressional intent because it would require upwind
areas to implement controls before the downwind area has implemented
all statutorily required or necessary controls.
While it is true that plans to meet the emissions budget for the
SIP call will be due prior to nonattainment designations and attainment
plans for areas designated nonattainment for the 8-hour standard, EPA
does not consider this result to be absurd in the present case.
The CAA, at least since its amendment in 1970, has required States
to regulate ozone. For more than the past 25 years, States have focused
on the adoption and implementation of local controls for the purpose of
bringing nonattainment areas into attainment. Thus, historically, the
downwind nonattainment areas have borne the brunt of the control
obligations through the implementation of local controls. In
comparison, areas in attainment of the NAAQS, but upwind of
nonattainment areas, have not been required to implement controls
designed to ameliorate the air quality problems experienced by their
downwind neighbors.
Since the CAA Amendment of 1977, designated nonattainment areas
have been subject to specific local control obligations, such as
vehicle I/M and, for stationary sources, the requirement to implement
RACT. The CAA Amendments of 1990 tightened these control obligations
for many areas. Moderate, serious, severe and extreme areas were
required to reduce emissions by 15 percent between 1990 and 1996. In
addition, each serious, severe and extreme area is required to achieve
9 percent reductions over the succeeding 3 year periods until the area
attains the

[[Page 57374]]

standard. Additional requirements, such as the use of RFG and the use
of vapor recovery devices on gasoline pumps, are also required for
certain areas (see generally, CAA section 182 and, e.g., section
211(k)). Thus, downwind areas with nonattainment problems under the 1-
hour NAAQS are under current obligations to submit SIP revisions
containing local control measures for that standard. For these areas,
local reductions needed to meet the 1-hour standard are already
occurring and will be achieved prior to or on the same schedule as
reductions States may require in response to the SIP call.
Furthermore, in many of the downwind areas, States have been taking
action to reduce ozone levels for many years in order to meet the 1-
hour ozone NAAQS. Although the fact that the 8-hour ozone NAAQS is a
new form of the ozone standard, however, should not obscure the fact
that the downwind States have been making efforts to reduce ozone
levels for decades. The EPA believes that the history of implementation
by downwind areas of ozone pollution controls further mitigates the
commenters' argument that it is absurd to require upwind areas to
implement controls in advance of downwind attainment demonstrations
under the 8-hour NAAQS.²³
---------------------------------------------------------------------------

\23\ Although the SIP call will provide a benefit to a wide
number of areas, the focus of the SIP call is to reduce boundary
conditions for a number of areas that will have difficulty attaining
either the 1-hour or 8-hour standard (or both) without the benefit
of reductions from outside the nonattainment area. Based on current
monitoring data and modeling, EPA predicts that there will be a
number of areas that are meeting the 1-hour standard that will be
designated nonattainment for the 8-hour standard. The EPA further
predicts that many of these areas will come back into attainment due
solely to the emission reductions achieved by the NO_X SIP
call. However, this incidental benefit--which likely will occur
without the need for local emission reductions--does not preclude
EPA from requiring the SIP call reductions, which are needed to help
other more seriously polluted areas that have long-standing
pollution problems.
---------------------------------------------------------------------------

Moreover, virtually all of the downwind States affected by today's
rulemaking, due to 8-hour ozone nonattainment or maintenance problems,
are themselves upwind contributors to problems further downwind, and,
thus, are subject to the same requirements as the States further
upwind.²⁴ The reductions these downwind States must
implement due to their additional role as upwind States will help
reduce their own 8-hour ozone problems on the same schedule as
emissions reductions for the upwind States. Accordingly, for the most
part, this rulemaking does not require upwind areas to take action in
advance of any action by downwind areas to ameliorate the downwind
problems.
---------------------------------------------------------------------------

\24\ Maine, New Hampshire, and Vermont are the only downwind
States that are not subject to today's action.
---------------------------------------------------------------------------

Finally, even if EPA were requiring upwind States to take action to
reduce downwind nonattainment and maintenance in advance of action by
the downwind States, this would simply require upwind areas to take the
first step by developing SIPs to eliminate their significant
contribution to the downwind problem. The downwind areas will be
required to take the next step by developing SIPs that address their
share. Generally, an agency may resolve a problem (in this case,
downwind nonattainment) on a step-by-step basis (see e.g., Group
Against Smog and Pollution, Inc. v. EPA, 665 F.2d 1284, 1291-92 (D.C.
Cir. 1981)).
A commenter has observed that under section 110(a)(1), EPA may
authorize section 110(a)(2) submittals as late as 3 years after
revision of a NAAQS, which, in this case, would run until July 2000.
The Early Planning Guidance, described above, indicates that States are
allowed until July 2000 to make submissions concerning other elements
of section 110(a)(2). However, as described elsewhere, EPA has
determined that the section 110(a)(2)(D) submittals should be submitted
by the end of September 1999 to assure that the required NO_X
reductions will be implemented as expeditiously as practicable, which
EPA has determined is no later than the May 1 start of the 2003 ozone
season (see Section V, below).
Citing section 107(a) of the CAA, the commenters assert that the
CAA requires downwind areas to fully adopt and implement all
statutorily required or necessary measures before EPA can require
upwind areas to control emissions. Section 107 provides that States
shall have the primary responsibility for assuring air quality within
the State by submitting a plan that specifies how the NAAQS will be
achieved and maintained in the State. The commenters attempt to read
this statement regarding a State's authority to choose the mix of
control measures within State boundaries as barring the control of
emissions from upwind States.
This provision may be read as focusing on the State-Federal balance
in controlling criteria pollutants, such as ozone, not any upwind-
State, downwind-State balance. The provision indicates that although
EPA may promulgate Federal measures that provide reductions to help
States reach attainment, States bear the ultimate responsibility for
assuring attainment. Further, this provision may be read to indicate
that States may choose the mix of controls to reach attainment within
their own boundaries. Nothing in this provision purports to address the
need for upwind controls. By comparison, section 110(a)(2)(D)
affirmatively requires States to submit a SIP prohibiting emissions
that significantly contribute to downwind nonattainment or interfere
with maintenance of the NAAQS. Thus, the statute, read as a whole,
contemplates that interstate transport will be addressed as part of the
downwind States' attainment responsibilities. Indeed, determining the
upwind area's share of the problem is necessary in order for downwind
attainment planning. In the absence of the upwind reductions that will
be achieved, the downwind area would be required to submit an
attainment plan to demonstrate attainment regardless of cost and
without benefit of the reduction of upwind emissions that significantly
contribute to nonattainment. In light of the statute as a whole, it is
absurd to argue that Congress intended downwind areas to reduce
emissions at any cost while upwind sources that significantly
contribute to that nonattainment remain unregulated. Congress attempted
to balance responsibilities, providing that States could choose the mix
of controls within the State's borders (CAA section 107(a)) and are
ultimately responsible for assuring attainment, but also recognizing
that emissions reductions from upwind States may be needed for
attainment (CAA section 110(a)(2)(D)(i)).
b. Process for Requiring SIP Submissions under the 8-Hour Standard.
The time by which the section 110(a)(2)(D) SIP revision under the 8-
hour NAAQS must be submitted is governed by section 110(a)(1), which
requires the SIP revision to be ``adopt[ed] and submit[ed] to the
Administrator, within 3 years (or such shorter period as the
Administrator may prescribe) after the promulgation of a [NAAQS] (or
any revision thereof) . . . .'' In the NPR, EPA indicated that the SIP
revision would be due by the end of September 1999, which EPA expected
to be 12 months from the date of completing today's final rule. In
today's action, EPA is confirming that the SIP revision will be due
September 30, 1999, for the reasons described below in Section VI.A.1,
Schedule for SIP Revision.
3. Requirements of Section 110(a)(2)(D)
a. Summary. Today's action is driven by the requirements of CAA
section 110(a)(2)(D). This provides that each SIP must--

[[Page 57375]]

* * * contain adequate provisions--(I) prohibiting, consistent
with the provisions of this title, any source or other type of
emissions activity within the State from emitting any air pollutant
in amounts which will--(I) contribute significantly to nonattainment
in, or interfere with maintenance by, any other State with respect
to any such national primary or secondary ambient air quality
standard * * *

According to section 110(a)(2)(D), the SIP for each area,
regardless of its designation as nonattainment or attainment (including
unclassifiable), must prohibit sources within the area from emitting
air pollutants in amounts that will ``contribute significantly'' to
``nonattainment'' in a downwind State, or that ``interfere with
maintenance'' in a downwind State.
b. Determination of Meaning of ``Nonattainment'' (1) Geographic
Scope. In determining the meaning and scope of section 110(a)(2)(D), it
is useful first to determine the geographic scope of ``nonattainment''
downwind.
At proposal, EPA stated that it--

* * * proposes to interpret this term to refer to air quality
and not to be limited to currently-designated nonattainment areas.
Section 110(a)(2)(D) does not refer to ``nonattainment areas,''
which is a phrase that EPA interprets to refer to areas that are
designated nonattainment under * * * section 107(d)(1)(A)(I) * * * .
Rather, the provision includes only the term `nonattainment' and
does not define that term. Under these circumstances, EPA has
discretion to give the term a reasonable definition, and EPA
proposes to define it to include areas whose air quality currently
violates the NAAQS, and will likely continue [to violate in the
future], regardless of the designation of those areas * * *

(62 FR 60324).
To determine whether areas would continue to violate in the future,
EPA proposed to take into account the reductions that would result from
current CAA control requirements (apart from controls that may be
required under section 110(a)(2)(D)). To take these reductions into
account, EPA determined whether the area would be in nonattainment in
the future based on air quality modeling that assumed CAA-mandated
reductions and that accounted for growth. If an area would reach
attainment based on required controls, EPA would not view that area as
having a nonattainment problem to which any upwind areas may be
considered to contribute.
As explained earlier, in today's action, EPA has determined that
for purposes of the 8-hour NAAQS, the reference to ``nonattainment''
should be defined as EPA proposed. Thus, in determining whether an
upwind area contributes significantly to ``nonattainment'' downwind,
EPA would evaluate downwind areas for which monitors indicate current
nonattainment, and air quality models indicate future nonattainment,
taking into account CAA control requirements and growth.
For the 1-hour standard, EPA proposed to define nonattainment to
include all grid cells within a county when a monitor in that county
indicated nonattainment. Upon further study, EPA found that in some
instances, a metropolitan area may consist of numerous counties, only a
few of which contain monitors indicating nonattainment. The EPA
recognizes that under the 1-hour NAAQS, nonattainment boundaries are
generally used to describe the area with the nonattainment problem;
accordingly, EPA believes that this geographic vicinity offers an
appropriate indication of an area that may be expected to have
nonattainment air quality. The EPA predicts that many 1-hour
nonattainment areas that currently monitor nonattainment somewhere
within the area will remain in nonattainment in 2007, in some cases
because of predicted violations in counties that currently monitor
attainment. The EPA believes that the entire area should be considered
to be in nonattainment until all monitors in the area indicate
attainment of the NAAQS. Thus, in today's action, EPA used the
designated nonattainment area in determining the downwind nonattainment
problem.²⁵
---------------------------------------------------------------------------

\25\ It should be reiterated that EPA relied on the designated
area solely as a proxy to determine which areas have air quality in
nonattainment. This proxy is readily available under the 1-hour
NAAQS because areas have long been designated nonattainment. The
EPA's reliance on designated nonattainment areas for purposes of the
1-hour NAAQS does not indicate that the reference in section
110(a)(2)(D)(i)(I) to ``nonattainment'' should be interpreted to
refer to areas designated nonattainment.
---------------------------------------------------------------------------

As noted above, commenters disagreed with EPA's view that the term
``nonattainment'' covers areas with air quality that is currently in
nonattainment, regardless of designation. The EPA's response to those
comments is also set forth above.
(2) 2007 Projection Year. In the NPR, EPA indicated that it would
adopt the year 2007 as the year for determining whether areas achieved
their required NO_X budget levels. Accordingly, in
determining whether downwind areas should be considered to be, and
remain in, ``nonattainment,'' EPA would model their air quality in
2007, based on the implementation of CAA required controls by that
date, and growth in emissions--generally due to economic growth and
greater use of vehicles--by that date. At proposal, EPA adopted this
same approach with respect to both the 1-hour and the 8-hour NAAQS (62
FR 60325). The EPA is continuing this approach.
c. Definition of Significant Contribution. As indicated in the NPR,
neither the CAA nor its legislative history provides meaningful
guidance for interpreting the term ``contribute significantly'' under
section 110(a)(2)(D)(i)(I).
(1) ``Contribute.'' The initial step in defining the ``contribute
significantly'' term is to determine the meaning of the term
``contribute.'' In the NPR, EPA stated that it believes this term
should be defined broadly, so that emissions ``contribute'' to
nonattainment downwind if they have an impact on nonattainment downwind
(62 FR 60325). Air quality modeling indicated that emissions from the
upwind States clearly impact downwind nonattainment problems; as a
result, EPA generally folded this step of determining whether sources
``contribute'' to nonattainment downwind into the step of determining
whether that contribution is ``significant,'' discussed below.
In addition, section 110(a)(2)(D)(i)(I) requires the SIP to
prohibit amounts of emissions ``which will contribute significantly * *
*'' (emphasis added). The EPA believes that the term ``will'' means
that SIPs are required to eliminate the appropriate amounts of
emissions that presently, or that are expected in the future,
contribute significantly to nonattainment downwind.
Because ozone is a secondary pollutant formed as a result of
complex chemical reactions involving numerous sources, it is not
possible to determine the downwind impact on each individual source. In
addition, ozone generally results from the contributions of numerous
sources. As indicated in the NPR:

[U]nhealthful levels of ozone result from emissions of
NO_X and VOCs from thousands of stationary sources and
millions of mobile sources [and consumer products and other sources]
across a broad geographic area. Each source's contribution is a
small percentage of the overall problem; indeed, it is rare for
emissions from even the largest single sources to exceed one percent
of the inventory of ozone precursors even for a single metropolitan
area. Under these circumstances, even complete elimination of any
given source's emissions may well have no measurable impact in
ameliorating the nonattainment problem. Rather, attainment requires
controls on numerous sources across a broad area. Ozone is a
regional scale

[[Page 57376]]

problem that requires regional scale reductions

(62 FR 60326).
Accordingly, EPA has adopted a ``collective contribution'' approach
to determining whether sources ``contribute'' to nonattainment
downwind: EPA determines the impact downwind of emissions in the
aggregate from a particular geographic region. If the aggregated
emissions are considered to contribute to nonattainment downwind, then
all of the emissions in that region should be considered as
contributors to that nonattainment problem. In today's action, EPA is
continuing the same interpretation of the term ``contribute,'' for the
reasons just described.
(2) ``Significantly''. (a) Notice of Proposed Rulemaking. In the
NPR, EPA proposed a ``weight-of-evidence,'' or multi-factor, approach
for determining whether a contribution is ``significant.''
The EPA proposed two separate interpretations for the term
``contribute significantly,'' which had implications as to which
factors were to be considered in what parts of the analysis. Under the
first interpretation, significant contribution is determined with
reference to--

* * * factors concerning amounts of emissions and their ambient
impact, including the nature of how the pollutant is formed, the
level of emissions and emissions density (defined as amount of
emissions per square mile) in the particular upwind area, the level
of emissions in other upwind areas, the amount of contribution to
ozone in the downwind area from the upwind areas, and the distance
between the upwind sources and the downwind nonattainment problem.
Under this approach, when emissions and ambient impact reach a
certain level, as assessed by reference to the factors identified
above, those emissions would be considered to ``contribute
significantly'' to nonattainment.

(62 FR 60325).
Under this interpretation, after identifying amounts of emissions
that constitute a significant contribution, EPA then determines the
amount of emissions reductions necessary to adequately mitigate these
contributions. This determination entails--

* * * [e]valuation of the costs of available measures for
reducing upwind emissions * * * as well as to the extent known (at
least qualitatively), the relative costs of, amounts of reductions
from, and ambient impact of measures available in the downwind areas.

Id.
Under the second interpretation, EPA considers all of the factors
under both the significant contribution prong and the mitigation prong
of the first interpretation, and, once EPA determines an amount of
emissions that does significantly contribute to downwind nonattainment,
then EPA would determine that the SIP must contain provisions adequate
to prohibit that amount of emissions. Id. at 60325-26.
(b) Today's Action. The EPA has determined that the second
interpretation should be used; that is, that the determination of
significant contribution includes both air quality factors relating to
amounts of upwind emissions and their ambient impact downwind, as well
as cost factors relating to the costs of the upwind emissions
reductions. Once an amount of emissions is identified in an upwind
State that contributes significantly to a nonattainment problem
downwind, or interferes with maintenance downwind, the SIP must include
provisions to eliminate that amount of emissions.
To reiterate, section 110(a)(2)(D)(i)(I) provides that the SIP must
``prohibit[]'' sources from ``emitting any air pollutant in amounts
which will contribute significantly to nonattainment in, or interfere
with maintenance by, any other State.'' The term ``prohibit'' is
defined as ``to forbid by authority'' or ``prevent,'' or ``preclude.''
``The American Heritage Dictionary of the English Language'' (3d ed.
1992, 1448). The EPA believes that the term ``prohibit'' means that
SIPs must eliminate those amounts of emissions determined to contribute
significantly to nonattainment or interfere with maintenance downwind.
Moreover, EPA believes that whether emissions ``contribute
significantly'' depends on a multifactor test, as described below.
Thus, section 110(a)(2)(D)(i)(I) does not require the elimination of
all upwind source emissions that impact downwind air quality problems,
but only those amounts of emissions that, based on a multi-factor test,
significantly contribute to downwind air quality problems.
d. Multi-factor Test for Determining Significant Contribution. In
the NPR, EPA proposed a multi-factor test for determining whether
emissions from an upwind State contribute significantly to a
nonattainment or maintenance problem downwind. The EPA received
numerous comments on the factors. Based on the comments and EPA's
further analysis, EPA, in today's action, is continuing the multi-
factor approach, with some refinements in response to comments, with
respect to the factors EPA considered and the manner in which EPA
considered them.
In determining whether emissions from upwind States affected by
today's action contribute significantly to downwind nonattainment or
maintenance problems, EPA specifically considered the following factors
with respect to each such upwind State. These factors were the primary
components in EPA's consideration.
' The overall nature of the ozone problem (i.e.,
``collective contribution'')
' The extent of the downwind nonattainment problems to
which the upwind State's emissions are linked, including the ambient
impact of controls required under the CAA or otherwise implemented in
the downwind areas
' The ambient impact of the emissions from the upwind
State's sources on the downwind nonattainment problems
' The availability of highly cost effective control
measures for upwind emissions.
The first three of these factors are related to air quality; the
fourth is related to costs.
In addition, EPA generally reviewed several other considerations
before concluding that upwind emissions contribute significantly to
downwind nonattainment. The EPA did not consider it necessary, or did
not have adequate information, to apply each of these factors with
specificity with respect to each upwind State's emissions. In addition,
in some instances, EPA did not have quantitative information to assess
certain of these factors, and instead relied on qualitative
information. These considerations were secondary aspects of EPA's
analysis. They include:
' The consistency of the regional reductions with the
attainment needs of the downwind areas with nonattainment problems
' The overall fairness of the control regimes required of
the downwind and upwind areas, including the extent of the controls
required or implemented by the downwind and upwind areas
' General cost considerations, including the relative
cost-effectiveness of additional downwind controls compared to upwind
controls
All of these factors and considerations are described in the
following sections.
e. Air Quality Factors. As noted above, EPA specifically considered
three air quality factors with respect to each upwind State, which
factors, in conjunction with the cost factor discussed in the next
section, were the primary components in EPA's consideration:
' The overall nature of the ozone problem (i.e.,
``collective contribution'')
' The extent of the downwind nonattainment problems to
which the upwind State's emissions are linked,

[[Page 57377]]

including the ambient impact of controls required under the CAA or
otherwise implemented in the downwind areas
' The ambient impact of the emissions from the upwind
State's sources on the downwind nonattainment problems
(1) Collective Contribution. As indicated elsewhere, ozone
generally results from the collective contribution of emissions from
numerous sources over a large geographic area. For example, for urban
nonattainment areas under the 1-hour NAAQS, the downwind sources,
comprise numerous stationary sources as well as mobile on-road sources,
mobile off-road sources, and consumer and commercial products. Further,
additional contributions are made by numerous upwind States, both
adjacent to and further away from the nonattainment area itself. The
fact that virtually every nonattainment problem is caused by numerous
sources over a wide geographic area is a factor suggesting that the
solution to the problem is the implementation over a wide area of
controls on many sources, each of which may have a small or
unmeasureable ambient impact by itself.
(2) Extent of Downwind Nonattainment Problems, Including Ambient
Impact of Required Controls. In determining whether a downwind area has
a nonattainment problem under the 1-hour standard to which an upwind
area may be determined to be a significant contributor, EPA determined
whether the downwind area currently has a nonattainment problem, and
whether that area area would continue to have a nonattainment problem
as of the year 2007 assuming that in that area, all controls
specifically required under the CAA were implemented, and all required
or otherwise expected Federal measures were implemented. If, following
implementation of such required CAA controls and Federal measures, the
downwind area would remain in nonattainment, then EPA considered that
area as having a nonattainment problem to which upwind areas may be
determined to be significant contributors.
Thus, this analytical approach assumes that downwind areas
implement all required controls and receive the benefit of reductions
from Federal measures, and yet have a residual nonattainment problem
(prior to the implementation of the regional reductions required by
today's action). The fact that a nonattainment problem persists,
notwithstanding fulfillment of CAA requirements by the downwind
sources, is a factor suggesting that it is reasonable for the upwind
sources to be part of the solution to the ongoing nonattainment
problem.
The EPA undertook a comparable analysis with respect to the 8-hour
NAAQS. That is, the major urban areas in the northeast, midwest, and
south that are violating the 8-hour NAAQS are designated nonattainment
under the 1-hour NAAQS as well. After these areas are designated
nonattainment under the 8-hour NAAQS, they will become subject to the
control requirements of section 172(c). However, for these areas, the
section 172(c) requirements do not, by their terms, impose any specific
controls other than what these areas have already implemented to
fulfill the requirements under section 182 attendant to their
designation and classification under the 1-hour NAAQS. Accordingly, the
same air quality modeling analyses that shows residual nonattainment
for at least one of the urban areas linked to each upwind State under
the 1-hour standard shows residual nonattainment for those areas under
the 8-hour NAAQS. Indeed, modeling analyses relied on for today's
action indicate residual nonattainment for the major urban areas even
after the implementation of regional reductions comparable to those
required today.²⁶
---------------------------------------------------------------------------

\26\ The presence of residual nonattainment in major urban areas
after their implementation of specifically required CAA controls
supports the regional reductions required under today's action.
Those regional reductions allow the major urban areas to progress
towards attainment under the 8-hour NAAQS, and, at the same time,
significantly ameliorate the nonattainment problems under the 8-hour
NAAQS for numerous other areas. In fact, EPA projections indicate
that numerous areas with nonattainment problems will achieve
attainment of the 8-hour NAAQS as a result of the regional reductions.
---------------------------------------------------------------------------

(3) Ambient Impact of Emissions from the Upwind Sources. In today's
action, EPA examined the impact of numerous upwind States on numerous
downwind areas with nonattainment problems.
Under the 1-hour NAAQS, EPA conducted various air quality modeling
analyses that examined the impact of emissions from sources in each
upwind State on ozone levels in downwind nonattainment areas, in light
of the impact of emissions from sources in other upwind States on the
downwind area's nonattainment problem. The EPA assessed the frequency
and magnitude of each upwind State's contribution to downwind
nonattainment problems. Some of the modeling analyses also permitted
determining the magnitude of the average contribution and the peak
contribution from each upwind State, as well as the percentage of each
upwind State's contribution to the downwind nonattainment problem.
The EPA determined that for each upwind State affected by today's
action, its contribution to a downwind nonattainment problem, in
conjunction with the contribution from other upwind States, comprised a
relatively large percentage of the nonattainment problem. The EPA
further determined that, in this context, the impacts from each
affected upwind State's NO_X emissions are sufficiently large
and/or frequent so that the amounts of that State's emissions should be
considered to be significant contributions, depending on the cost
factor and other relevant considerations. For most upwind States, EPA
conducted two types of modeling--UAM-V and CAMx--that isolated the
impact of emissions from the upwind State alone on downwind
nonattainment.
The EPA also conducted much the same analysis to determine the
impact of emissions from each upwind State on ozone levels in downwind
States under the 8-hour NAAQS. Because nonattainment problems under the
8-hour NAAQS are widespread, and because EPA has not designated
individual nonattainment areas, EPA focused this part of its inquiry on
the upwind State's impact on the entire downwind State.
The EPA's analysis under both the 1-hour and 8-hour NAAQS led EPA
to conclude that, in light of both the collective contribution nature
of the ozone problem, and the fact that downwind areas continue to
suffer a nonattainment problem even after implementation of all
required CAA measures and Federal measures, emissions from each of the
affected upwind States have a sufficiently large and/or frequent
ambient impact such that those emissions contribute significantly to
nonattainment downwind, depending on the availability of highly cost-
effective measures and on other considerations discussed below.
f. Determination of Highly Cost-effective Reductions and of
Budgets. After determining the degree to which NO_X
emissions, as a whole from the particular upwind States, contribute to
downwind nonattainment or maintenance problems, EPA then determined
whether any amounts of the NO_X emissions may be eliminated
through controls that, on a cost-per-ton basis, may be considered to be
highly cost effective. By examining the cost effectiveness of recently
promulgated or proposed NO_X controls, EPA determined that an
average of approximately $2,000 per ton removed

[[Page 57378]]

is highly cost effective. The EPA then determined a set of controls on
NO_X sources that would cost no more than an average of
$2,000 per ton reduced. Specifically, EPA determined that one set of
these controls would include a cap-and-trade program for (i)
electricity generating boilers and turbines larger than 25 Mwe (``large
EGUs''), and (ii) large non-electricity generating industrial boilers
and turbines (``large non-EGU boilers and turbines''). The application
of an emission rate of 0.15 lb/mmBtu and 1995-1996 utilization for EGUs
and 60 percent for large non-EGUs to the emissions projected to occur
in 2007 including growth and CAA measures, led to the determination of
the amounts to be reduced. The remaining amount is a State's budget.
The EPA further determined that additional highly cost-effective
controls are also available for cement manufacturing sources and
internal combustion engines. On the basis of reasonable assumptions
concerning growth to the year 2007, EPA then determined the amounts of
emissions from these source categories that would be eliminated with
those controls.
The EPA further determined that there were no other controls on
other NO_X sources that qualify as highly cost effective
(although several controls are reasonably cost-effective).
On the basis of the determinations just described for the various
source categories, EPA determined an amount of NO_X emissions
that may be eliminated through these highly cost-effective measures.
Because EPA had also determined that the NO_X emissions from
the affected upwind States have a large and/or frequent impact on
downwind nonattainment or maintenance problems, EPA concludes that the
amount of NO_X emissions from those States that can be
eliminated through application of highly cost-effective control
measures contributes significantly to nonattainment or maintenance
problems downwind.
Under section 110(a)(2)(D)(i)(I), the SIP must include ``adequate
provisions prohibiting'' sources from emitting these ``amounts.''
Because no highly cost-effective controls are available to eliminate
the remaining amounts of NO_X emissions, EPA concludes that
those emissions do not contribute significantly to downwind
nonattainment or maintenance problems. As indicated below and in
Section III, there are cost-effective alternatives available to States
that choose not to adopt all of the highly cost-effective measures on
which EPA based its selection of the significant amounts of
NO_X emissions.
To implement EPA's determinations, each affected upwind State is
required to submit for EPA approval SIP controls projected to be
sufficient, by the year 2007, to eliminate the amount of NO_X
emissions in the State that EPA determined contributes significantly to
nonattainment. The EPA determined this amount of reductions, for each
affected upwind State, as follows: EPA first determined the amount of
NO_X emissions in that State by the year 2007, based on
assumptions concerning both growth and emissions controls that are
required under the CAA or that will be implemented due to Federal
actions (the ``2007 base case''). Second, EPA applied the control
measures identified as highly cost effective to the 2007 base case
amount for the appropriate source categories. The amount of
NO_X emissions remaining in the State after application of
controls to the affected source categories constitutes the 2007 budget.
The difference between the 2007 base case and the 2007 budget is the
amount of NO_X emissions in that State by the year 2007 that
EPA has determined to contribute significantly to nonattainment and
that, therefore, the SIPs must prohibit.
The upwind State's SIP revision due in response to today's action
must provide controls that, on the basis of the same assumptions
(including concerning growth) made by EPA in determining the budget,
would limit NO_X emissions in the year 2007 to no more than
the 2007 budget. The State has full discretion in selecting the
controls, so that it may choose any set of controls that would assure
achievement of the budget.
As EPA stated in the NPR:

States are not constrained to adopt measures that mirror the
measures EPA used in calculating the budgets. In fact, EPA believes
that many control measures not on the list relied upon to develop
EPA's proposed budgets are reasonable--especially those, like
enhanced vehicle inspection and maintenance programs, that yield
both NO_X and VOC emissions reductions.[ ²⁷]
Thus, one State may choose to primarily achieve emissions reductions
from stationary sources while another State may focus emission
reductions from the mobile source sector.

\27\ As indicated in the NPR, EPA considers that measures may be
reasonable in light of their reduction of VOC and NO_X
emissions, even though their cost-effectiveness in terms of cost per
NO_X emissions removed is relatively high (62 FR 60346-48).
---------------------------------------------------------------------------

(62 FR 60328).
The EPA believes that its overall approach derives further support
from the mandate in section 110(a)(2)(D) that each SIP include
provisions prohibiting ``any source or other type of emissions activity
within the State from emitting any air pollutant in amounts' that
adversely affect downwind areas. The phrase ``any source or other type
of emissions activity'' may be interpreted to require that the SIP
regulate all sources of emissions to assure that the total amount of
emissions generated within the State does not adversely affect downwind
areas. By its terms, the phrase covers all emitters of any kind because
every emitter--stationary, mobile, or area--may be considered a
``source or other type of emissions activity.'' This interpretation is
consistent with the legislative history of the phrase. Prior to the CAA
Amendments of 1990, the predecessor to section 110(a)(2)(D), which was
section 110(a)(2)(E), referred to ``any stationary source within the
State.'' In the 1990 Amendments, Congress revised the phrase to read as
it currently does. A Committee Report explained, ``Where prohibitions
in existing section 110(a)(2)(E) apply only to emissions from a single
source, the amendment includes ``any other type of emissions
activity,'' which makes the provision effective in prohibiting
emissions from, for example, multiple sources, mobile sources, and area
sources.'' V Leg. Hist. 8361, S. Rep. No. 228, 101st Cong., 1st Sess.
21 (1989).
For reasons explained below, if an upwind State chooses to achieve
all or a portion of the required reductions from large EGUs or large
non-EGU boilers and turbines, then the SIP must include a mass
emissions limitation for those sources computed with reference to
certain growth assumptions and the emission rate limits chosen by the
State. The EPA recommends that this mass limitation, or cap, be
accompanied by a trading program. Any such cap-and-trade program must
be established by May 1, 2003. If the State chooses to achieve all or a
portion of the required reductions from other sources, then the State
must implement controls, by the year 2003, on those other sources that
are projected to achieve the required level of reductions, based on
certain assumptions (including growth), in the year 2007. The controls
on these other sources may be rate-based, and no emissions cap on them
is required. By the year 2007, any applicable mass emissions limitation
for large EGUs or large non-EGU boilers and turbines must continue to
be met, and any applicable controls on other sources must continue to
be implemented. The amount of the 2007 overall budget is used to
compute the level of controls that would result in the appropriate
amount of emissions reductions, given assumptions concerning, for example,

[[Page 57379]]

growth. To this extent, the 2007 overall budget is an important
accounting tool. However, the State is not required to demonstrate that
it has limited its total NO_X emissions to the budget
amounts. Thus, the overall budget amount is not an independently
enforceable requirement.
g. Other Considerations in Determination of Significant
Contribution. The EPA reviewed several other considerations in support
of its determination that the specified amounts of emissions from the
affected upwind States contribute significantly to nonattainment downwind.
(1) Consistency of Regional Reductions with Downwind Attainment
Needs. The EPA conducted modeling analyses of emission reductions of
virtually the same magnitude as the regional reductions required under
today's action. Although the impact on any downwind ozone problem of
each upwind State's emissions reductions alone may be relatively small,
the impact of those reductions, when combined with the reductions from
the other States, is substantial. Based on this modeling, EPA
determined that the regional reductions allow downwind nonattainment
areas under the 1-hour NAAQS to make appreciable progress towards
attainment. The EPA further determined that under the 8-hour NAAQS,
many areas with nonattainment problems are expected to reach attainment
based solely on the regional reductions, and that other (primarily
urban) areas would benefit from the regional reductions but are
expected to experience residual nonattainment. EPA further determined
that none of the upwind States affected by today's action are affected
by ``overkill,'' that is, required reductions that are more than
necessary to ameliorate downwind nonattainment in every downwind area
affected by that upwind State.
(2) Fairness. The EPA also considered the overall fairness of the
control regimes required of the downwind and upwind areas, including
the extent of the controls required or implemented by the downwind and
upwind areas. Most broadly, EPA believes that overall notions of
fairness suggest that upwind sources which contribute significant
amounts to the nonattainment problem should implement cost-effective
reductions. When upwind emitters exacerbate their downwind neighbors'
ozone nonattainment problems, and thereby visit upon their downwind
neighbors additional health risks and potential clean-up costs, EPA
considers it fair to require the upwind neighbors to reduce at least
the portion of their emissions for which highly cost-effective controls
are available.
In addition, EPA recognizes that in many instances, areas
designated as nonattainment under the 1-hour NAAQS have incurred ozone
control costs since the early 1970s. Moreover, virtually all components
of their NOx and VOC inventories are subject to SIP-required or Federal
controls designed to reduce ozone. Furthermore, these areas have
complied with almost all of the specific control requirements under the
CAA, and generally are moving towards compliance with their remaining
obligations. The CAA's sanctions and FIP provisions provide assurance
that these remaining controls will be implemented. By comparison, many
upwind States in the midwest and south have had fewer nonattainment
problems and have incurred fewer control obligations.
(3) General Cost Considerations. The EPA also considered the fact
that in general, areas that currently have, or that in the past have
had, nonattainment problems under the 1-hour NAAQS, or that are in the
Northeast Ozone Transport Region (OTR), have already incurred ozone
control costs. The controls already implemented in these areas tend to
be among the less expensive of available controls. As described in more
detail below, EPA has determined that, in general, the next set of
controls identified as available in the downwind nonattainment areas
under the 1-hour NAAQS would cost approximately $4,300 per ton removed.
By comparison, EPA has determined that the cost of the regional
reductions required today would approximate $1,500 per ton removed.
Thus, it appears that the upwind reductions required by today's action
are more cost-effective per ton removed than reductions in the downwind
nonattainment areas. Moreover, under the 1-hour NAAQS, the reductions
required from each upwind State, in conjunction with reductions from
other upwind States, result in ambient improvement in at least several
downwind areas with nonattainment problems.
The EPA did not have available, and was not presented with,
meaningful quantitative information indicating the cost-effectiveness
of the regional reductions required today in light of their ambient
impact downwind (e.g., the cost of emissions reductions per ppb
improvement in ambient ozone levels in a downwind nonattainment area).
This lack of information limited the extent to which EPA could rely on
this consideration in making its determinations.
The various considerations just discussed point in the same
direction as the other factors described above concerning air quality
and costs. These factors and considerations lead EPA to conclude that
the amounts of each upwind State's emissions that may be eliminated
through highly cost-effective measures contribute significantly to
nonattainment or maintenance problems downwind.
h. Interfere with Maintenance. Once a nonattainment area has
attained the NAAQS, it is required to maintain that standard (e.g.,
sections 107(d)(3)(E)(iv), 110(a)(1)). Section 110(a)(2)(D)(i)(I) also
requires that SIPs contain adequate provisions prohibiting amounts of
emissions that ``interfere with maintenance by * * * any [downwind]
State.'' The EPA explained and applied this requirement in the NPR as
follows:

This [interfere-with-maintenance] requirement * * * does not, by
its terms, incorporate the qualifier of ``significantly.'' Even so,
EPA believes that for present purposes, the term ``interfere''
should be interpreted much the same as the term ``contribute
significantly,'' that is, through the same weight-of-evidence approach.
With respect to the 1-hour NAAQS, the ``interfere-with-
maintenance'' prong appears to be inapplicable. The EPA has
determined that the 1-hour NAAQS will no longer apply to an area
after EPA has determined that the area has attained that NAAQS.
Under these circumstances, emissions from an upwind area cannot
interfere with maintenance of the 1-hour NAAQS.
With respect to the 8-hour NAAQS, the ``interfere-with-
maintenance'' prong remains important. After an area has reached
attainment of the 8-hour NAAQS, that area is obligated to maintain
that NAAQS. (See sections 110(a)(1) and 175A.) Emissions from
sources in an upwind area may interfere with that maintenance.
The EPA proposes to apply much the same approach in analyzing
the first component of the ``interfere-with-maintenance'' issue,
which is identifying the downwind areas whose maintenance of the
NAAQS may suffer interference due to upwind emissions. The EPA has
analyzed the ``interfere-with-maintenance'' issue for the 8-hour
NAAQS by examining areas whose current air quality is monitored as
attaining the 8-hour NAAQS [or which have no current air quality
monitoring], but for which air quality modeling shows nonattainment
in the year 2007. This result is projected to occur, notwithstanding
the imposition of certain controls required under the CAA, because
of projected increases in emissions due to growth in emissions
generating activity. Under these circumstances, emissions from
upwind areas may interfere with the downwind area's ability to
attain. Ascertaining the impact on the downwind area's air quality
of the upwind area's emissions aids in determining whether the
upwind emissions interfere with maintenance

[[Page 57380]]

(62 FR 60326).
In today's action, EPA is taking the same positions with respect to
the interfere-with-maintenance test as described in the NPR. Because
EPA generally interprets the ``interfere-with-maintenance'' test the
same as the ``contributes-significantly-to-nonattainment'' test, for
purposes of convenience, in this final rule, EPA sometimes refers to
``contributes-significantly-to-nonattainment'' to refer to both tests.
i. Dates. In today's action, EPA is determining that SIP
submissions required under this rulemaking must be submitted by
September 30, 1999 (see Section VI.A.1, Schedule for SIP Revision).
Further, in today's action, EPA is requiring that SIP controls
required today must be implemented by no later than May 1, 2003, and
they must achieve reductions computed with reference to an overall
budget amount determined as of September 30, 2007 (see Section V,
NO_X Control Implementation and Budget Achievement Dates).
j. Downwind Areas' Control Obligations. Commenters have argued that
under the CAA, downwind States must implement additional controls
before EPA may require controls in upwind States. Commenters base this
argument in part on the provisions of CAA section 107(a), which provides,

Each State shall have the primary responsibility for assuring
air quality within the entire geographic area comprising such State
by submitting an implementation plan for such State which will
specify the manner in which [NAAQS] will be achieved and maintained
within each air quality control region in such State.

Commenters further note that downwind States must implement
additional reductions (beyond those specifically required by the CAA
²⁸) as needed to attain, under section 182(b)(1)(A)(i) and
182(c)(2)(A). The commenters add that section 179(d)(2) is a generally
applicable provision that limits the stringency of required controls to
what is feasible. The commenters read these provisions together to
conclude that downwind States must first implement all feasible control
measures in an effort to reach attainment, and only after EPA
determines that such States have done so but have not reached
attainment may EPA require upwind contributors to implement controls.
The commenters further observe that some of the downwind States in the
Northeast have not implemented all feasible SIP measures.
---------------------------------------------------------------------------

\28\ Reductions specifically required by the CAA include, for
example, the 3 percent-per-year ROP reductions required of ozone
nonattainment areas classified as serious or higher, under section
182(c)(2)(B).
---------------------------------------------------------------------------

The EPA disagrees with this legal analysis. The provision in
section 107(a) that accords to States the primary responsibility for
the air quality of their air basins, in essence provides the underlying
rationale for the requirement of States to submit SIP revisions that
meet CAA requirements. This phrase clarifies that the requirement of
assuring attainment does not fall, in the first instance, on EPA. This
provision does not have implications for apportioning responsibility
between the downwind State and upwind States for contributions from
upwind States. Downwind States would still carry the primary
responsibility of assuring clean air even after the upwind contributors
have revised their SIPs to meet the requirements of section 110(a)(2)(D).
Furthermore, EPA disagrees that section 179(d)(2) has any
application to today's rulemaking. That provision in essence provides a
general rule that if a nonattainment area fails to attain by its
attainment date, EPA may require the State to implement reasonable
controls that can be ``feasibly implemented.'' This requirement is not
relevant to today's rulemaking, which addresses the requirements under
section 110(a)(2)(D)(i)(I) that SIPs include provisions eliminating
amounts of emissions from their sources that contribute significantly
to downwind nonattainment.
In addition, the requirement of downwind States to implement
reductions beyond minimum CAA requirements if needed for attainment
does not place the burden of implementing those reductions, in the
first instance, on the downwind States. This requirement should be read
to go hand-in-hand with the section 110(a)(2)(D) requirement that
upwind States include SIP provisions that prohibit their sources from
emitting air pollutants in amounts that ``significantly contribute'' to
downwind nonattainment. In today's action, EPA is promulgating criteria
for interpreting section 110(a)(2)(D) to take into account downwind
attainment needs.
As a practical matter, EPA has reviewed the status of Northeast
States' efforts to comply with the requirements of the 1990 CAA
Amendments and has found that these States have complied with the vast
majority of the SIP submission requirements. Even so, EPA is well aware
that some of the States have not made certain required submissions.
^29-30 However, EPA sees no basis in section 110(a)(2)(D) to
mandate that downwind areas complete their SIP planning and
implementation before upwind areas are required to begin that process.
Upwind areas have been subject to the requirements of section
110(a)(2)(D)--in some form--since the predecessor to this provision was
added in the 1977 CAA Amendments. The EPA has determined, through air
quality modeling, that even after the downwind States fulfill their
prescribed CAA requirements, they will have areas expected to remain in
nonattainment. Under these circumstances, the downwind areas continue
to constitute areas with air quality in ``nonattainment'' under section
110(a)(2)(D). As a result, upwind areas with emissions in amounts that
``significantly contribute'' to the nonattainment air quality downwind
are subject to control requirements whether or not the downwind areas
they affect have met all of their planning obligations.
---------------------------------------------------------------------------

\29-30\ If downwind areas fail to meet their planning
obligations, they are subject to sanctions (See Section VI, below.
As EPA noted in the NPR, 62 FR 60322-23, in some instances, States
in the Northeast failed to submit all of their required SIP
revisions or other commitments under Phase 1 of the March 2, 1995
Memorandum and as a result, EPA initiated the sanctions process by
starting sanctions clocks. In general, those States have since made
the required Phase 1 submissions, and EPA terminated the sanctions
process by stopping the clocks.
---------------------------------------------------------------------------

k. Section 110(a)(2)(D) Caselaw. In the NPR, EPA noted that prior
to the CAA Amendments of 1990, EPA had issued several rulemakings under
section 110(a)(2)(E), the predecessor to section 110(a)(2)(D), and
section 126 that addressed the issue of significant contribution in the
context of pollutant transport. In those rulemakings, EPA generally
applied a multi-factor test to determine whether the emissions from the
sources in question constituted a signficant contribution to downwind
jurisdictions. In each instance, EPA concluded that the emissions at
issue from the upwind sources were not demonstrated to impact downwind
air quality in a manner that would constitute significant contribution.
Several of these determinations resulted in judicial challenges, but in
each instance the courts upheld the Agency's determination of no
significant contribution. The EPA indicated in the NPR that the prior
rulemakings and the related court holdings, provide limited precedents
for today's action. The EPA noted that these decisions have limited
relevance because they involved different facts and circumstances,
including different pollutants, different

[[Page 57381]]

upwind sources, and different downwind effects.
Several commenters asserted that these prior rulemakings and cases
are relevant to today's action, and compel EPA to conclude that the
emissions from the upwind States affected by today's action do not
contribute significantly to downwind nonattainment or maintenance
problems. The EPA disagrees that these earlier determinations are
controlling and that these earlier determinations are inconsistent with
today's action. The EPA responds to these comments in detail in the
Response to Comment document.

B. Alternative Interpretation of Section 110(a)(2)(D)

As discussed above, in the NPR EPA advanced an alternative
interpretation of section 110(a)(2)(D) (62 FR 60327). Under this
alternative interpretation, EPA would determine the level of emissions
that significantly contribute to nonattainment downwind based on
factors relating to the entire amount of upwind emissions from a
particular upwind State and their ambient impact downwind. The EPA
would then determine what emissions reductions must be required to
adequately mitigate that significant contribution based on factors
relating to cost effectiveness of reductions and attainment needs downwind.
The EPA continues to believe that this alternative interpretation
remains a permissible interpretation of the statute for the reasons
described in the NPR (62 FR 60327). In any event, it should be noted
that for purposes of today's action, EPA finds no practical difference
between the requirements that would result from the interpretation of
section 110(a)(2)(D) adopted today and those that would result from the
alternative interpretation described in the NPR. That is, even under
the alternative interpretation, today's rulemaking would contain the
same findings and require the same SIP revisions as under the
interpretation adopted today (62 FR 60327).

C. Weight-of-Evidence Determination of Covered States

As discussed above, EPA applied a multi-factor approach to identify
the amounts of NO_X emissions that contribute significantly
to nonattainment. The EPA evaluated three air quality factors for each
upwind jurisdiction (hereafter referred to as ``States'' or ``upwind
States'') to determine whether each has emissions whose contributions
to downwind nonattainment problems are large and/or frequent enough to
be of concern. Further, for those States whose emissions are large and/
or frequent enough to be of concern, EPA applied highly cost-effective
controls to determine the amount of NO_X in upwind States
which significantly contributes to nonattainment in, or interferes with
maintenance by, a downwind State. The EPA also generally reviewed
several other considerations before drawing final conclusions. Even
though the actual finding of significant contribution applies only to
the portion of a State's emissions for which EPA has identified highly
cost-effective controls, for ease of discussion, the term
``significant'' (or like term) is used in the discussion in this
section to characterize the emissions of each upwind State that make a
large and/or frequent contribution to nonattainment in downwind States
sufficient to warrant eliminating a portion of its emissions equivalent
to what can be removed through those controls.
The purpose of this section is to describe the technical analyses
performed by EPA to (a) quantify the air quality contributions from
emissions in each upwind State on both 1-hour and 8-hour nonattainment,
as well as 8-hour maintenance, in each downwind State, and (b)
determine whether these contributions are significant.
In the proposed weight-of-evidence approach, EPA specifically
applied several factors to each upwind State, as discussed in Section
II.A.3.c, Definition of Significant Contribution. These factors
include:
. The overall nature of ozone problem (i.e., ``collective
contribution'');
. The extent of the downwind nonattainment problems to which
the upwind State's emissions are linked, including the ambient impact
of controls required under the CAA or otherwise implemented in the
downwind areas; and
. The ambient impact of the emissions from the upwind
State's sources on the downwind nonattainment problems.
As part of the analysis of these factors, EPA considered the
findings from OTAG's technical analyses, as well as the findings from a
number of other studies performed by OTAG participants independent of
OTAG. The major findings from these analyses are described below. This
is followed by an overview of the approach used by EPA in the proposal
for considering the above factors to identify States that make a
significant contribution to downwind nonattainment. The comments and
EPA's response to comments on EPA's weight-of-evidence proposal are
then discussed. Following that discussion, the results of additional
State-by-State UAM-V modeling and State-by-State CAM_X
³¹ source apportionment modeling performed by EPA in
response to comments are summarized.³² The EPA's analysis of
the modeling results in terms of the significance of the contributions
of upwind States to downwind nonattainment is presented in Section
II.C.4, Confirmation of States Making a Significant Contribution to
Downwind Nonattainment.
---------------------------------------------------------------------------

\31\ Comprehensive Air Quality Model with Extensions.
\32\ The UAM-V and CAM_X models are described in the
Air Quality Modeling TSD.
---------------------------------------------------------------------------

1. Major Findings From OTAG-Related Technical Analyses
The major findings from the air quality and modeling analyses by
OTAG and individual OTAG participants that are most relevant to today's
rulemaking are as follows:
. several different scales of transport (i.e., intercity,
intrastate, interstate, and inter-regional) are important to the
formation of high ozone in many areas of the East;
. emissions reductions in a given multistate region/
subregion have the most effect on ozone in that same region/subregion;
. emissions reductions in a given multistate region/
subregion also affect ozone in downwind multistate regions/subregions;
. downwind ozone benefits decrease with distance from the
source region/subregion (i.e., farther away, less effect);
. downwind ozone benefits increase as the size of the upwind
area being controlled increases, indicating that there is a cumulative
benefit to extending controls over a larger area;
. downwind ozone benefits increase as upwind emissions
reductions increase (the larger the upwind reduction, the greater the
downwind benefits);
. a regional strategy focusing on NO_X reductions
across a broad portion of the region will help mitigate the ozone
problem in many areas of the East;
. both elevated and low-level NO_X reductions
decrease ozone concentrations regionwide;
. there are ozone benefits across the range of controls
considered by OTAG; the greatest benefits occur with the most emissions
reductions; there was no ``bright line'' beyond which the benefits of
emissions reductions diminish significantly;
. even with the large ozone reductions that would occur if the most

[[Page 57382]]

stringent controls considered by OTAG were implemented, there may still
remain high concentrations in some portions of the OTAG region; and a
regional NO_X emissions reduction strategy coupled with local
NO_X and/or VOC reductions may be needed to enable attainment
and maintenance of the NAAQS in this region.
The above findings provide technical evidence that transport within
portions of the OTAG region results in large contributions from upwind
States to ozone in downwind areas, and that a regionwide approach to
reduce NO_X emissions is an effective way to address these
interstate contributions.
2. Summary of Notice of Proposed Rulemaking Weight-of-Evidence Approach
The EPA relied on OTAG data to develop the information necessary to
evaluate the weight-of-evidence factors identified above. These data
include emissions (tons) and emission density (tons per square mile),
air quality analyses, trajectory, wind vector, and ``ozone cloud''
analyses, and subregional zero-out modeling. In brief, EPA's proposed
approach was as follows:
. the OTAG transport distance scale was applied to identify,
based on the meteorological potential for transport, which States may
contribute to ozone in downwind States;
. the results of the OTAG subregional modeling runs
(described below) were used to quantify the extent to which each
subregion contributes to downwind nonattainment for the 1-hour and/or
8-hour NAAQS;
. the OTAG 2007 Base Case NO_X emissions and
emissions density were used to identify States which emit large amounts
of NO_X and/or have a high density of NO_X
emissions compared to other States in the OTAG region and, therefore,
have NO_X emissions which may be great enough to contribute
to downwind nonattainment; and the OTAG 2007 Base Case NO_X
emissions were also used to translate the findings from the subregional
modeling to a State-by-State basis.
a. Quantification of Contributions. As part of OTAG's assessment of
transport, a series of model runs were performed to examine the impacts
of emissions from each of 12 multistate subregions on ozone in downwind
areas. The locations of these subregions are shown in Figure II-1.

[GRAPHIC] [TIFF OMITTED] TR27OC98.000

In each subregional model run, all manmade emissions were removed
from one upwind subregion and the model was run for the OTAG July 1988
and 1995 episodes. The ``parts per billion (ppb)'' differences in ozone
between each subregional zero-out run compared to the corresponding
2007 Base Case run were used to quantify the air quality impacts of the
subregion on nonattainment downwind.
In the proposed NO_X SIP call, EPA considered areas as
``nonattainment'' if air quality monitoring indicates that the area is
currently measuring nonattainment and if air quality modeling indicates
future nonattainment, taking into account CAA control requirements and
growth. In this regard, areas were considered nonattainment for the 1-
hour NAAQS if

[[Page 57383]]

they had 1994-1996 \33\ monitoring data indicating measured 1-hour
violations and 2007 Base Case 1-hour predictions >=125 ppb. Areas were
considered to be nonattainment for the 8-hour NAAQS if they had 1994-
1996 monitoring data indicating measured 8-hour violations and 2007
Base Case 8-hour predictions >=85 ppb. The inconsistency between the
form of the 8-hour NAAQS, which considers 3 years of data for
determining the average of the fourth-highest 8-hour daily maximum
concentration at a monitor, and the limited predictions available from
the OTAG episodes introduced a complication to the analysis of 8-hour
contributions. It was not possible to use the model predictions in a
way that explicitly matched the form of the 8-hour NAAQS. Instead, an
analysis of seasonal and episodic ozone measurements was performed in
an attempt to link 8-hour measured concentrations during the OTAG
episodes to the form of the 8-hour NAAQS, as closely as possible. The
results of that analysis indicated that the 3-episode average of the
second highest 8-hour ozone concentrations measured during the OTAG
1991, 1993, and 1995 episodes corresponded best, overall, to the 3-year
average of the fourth highest 8-hour daily ambient data. However, since
OTAG subregional modeling was only available for the 1988 and 1995
episodes, EPA used the concentrations during these two episodes in
calculating average second high 8-hour concentrations.\34\
---------------------------------------------------------------------------

\33\ Data for 1994-1996 were used because these were the most
recent quality-assured data available at the time the analysis was
performed.
\34\ In response to comments, EPA has reexamined the method for
relating 8-hour model predictions during the OTAG episodes to the
form of the 8-hour NAAQS. This is discussed further in Section
II.C.2.c, Comments and Responses on the Proposed Weight of Evidence
Approach to Significant Contribution.
---------------------------------------------------------------------------

b. Evaluation of 1-Hour and 8-Hour Contributions. In the proposal,
EPA summarized the ``ppb'' contributions to downwind nonattainment from
each subregion in terms of both the frequency and the magnitude of the
downwind impacts over specific concentration ranges (e.g., 2 to 5 ppb,
5 to 10 ppb, 10 to 15 ppb, etc.). The results indicate that, in
general, large contributions to downwind nonattainment occur on
numerous occasions. Although the level of downwind contribution varies
from subregion to subregion, a consistent pattern is apparent for both
1-hour nonattainment and 8-hour nonattainment. Specifically, the
results of the subregional modeling indicate that emissions from States
in subregions 1 through 9 produce large 1-hour and 8-hour contributions
downwind in terms of the magnitude and frequency, including geographic
extent, of the downwind impacts. In addition, nonattainment areas
within many States in the OTAG region receive large and/or frequent
contributions from emissions in these subregions. The EPA proposed to
find that most of the States whose emissions are wholly or partially
contained within one or more of these subregions (i.e., Alabama,
Connecticut, Delaware, Georgia, Illinois, Indiana, Kentucky, Maryland,
Michigan, Missouri, New Jersey, New York, North Carolina, Ohio,
Pennsylvania, South Carolina, Tennessee, Virginia, West Virginia, and
Wisconsin, as well as the District of Columbia) are making a
significant contribution to downwind nonattainment. In addition to the
ambient impact demonstrated by the subregional modeling, this proposed
finding was based on a determination that:
. OTAG strategy modeling and non-OTAG modeling indicate that
NO_X emissions reductions across these States would produce
large reductions in 1-hour and 8-hour ozone concentrations across broad
portions of the region including 1-hour and 8-hour nonattainment areas;
. these States are upwind from nonattainment areas within
the 1- to 2-day distance scale of transport;
. these States form a contiguous area of manmade emissions
covering most of the core portion of the OTAG region;
. 11 of the States that are wholly within subregions 1
through 9 have a relatively high level of NO_X emissions from
sources in their States; these States are ranked in the top 50 percent
of all States in the region in terms of total NO_X emissions
and/or have NO_X emissions exceeding 1000 tons per day;
. States wholly within subregions 1 through 9 with lesser
emissions have a relatively high density of NO_X emissions;
. for the seven States that are only partially contained in
one of subregions 1 through 9, the State total NO_X
emissions, as well as each State's contribution to NO_X
emissions in the subregions in which they are located, indicate that
six of the States each have: NO_X emissions that are more
than 10 percent of the total NO_X emissions in one of these
subregions, NO_X emissions in the top 50 percent among all
States, and/or a majority of its NO_X emissions within one of
these subregions.
For the New England States that were not included in any of the
OTAG zero-out subregions, EPA found that two of these States (i.e.,
Massachusetts and Rhode Island) have a high density of NO_X
emissions. Also, the trajectory and wind vector analyses indicated that
these States are immediately upwind of nonattainment areas in other States.
For the nine States in the OTAG region which are wholly within
subregions 10, 11, and 12 (i.e., Florida, Kansas, Louisiana, Minnesota,
Nebraska, North Dakota, Oklahoma, South Dakota, and Texas), and for
Arkansas, Iowa, and Mississippi, EPA proposed that emissions from each
of these States should be considered not to significantly contribute to
downwind nonattainment. These States are further discussed below in
Section II.C.5, States Not Covered by this Rulemaking.
c. Comments and Responses on Proposed Weight-of-Evidence Approach
to Significant Contribution. The EPA received a number of comments on
various elements of the proposed weight-of-evidence approach. In
addition, EPA received new modeling and analyses performed by
commenters which address the issue of significant contribution. The
following is a summary of the major comments received by EPA and the
responses to these comments. Additional comments and EPA's response to
these comments are provided in the Response to Comment document.
Comment: Some commenters stated that it was inappropriate to use a
weight-of-evidence approach to determine the significance of upwind
emissions on downwind nonattainment. Rather, it was argued that EPA
should use a specific ``bright line'' criterion. Other commenters
supported the weight-of-evidence approach.
Response: The magnitude and frequency of contributions from an
upwind State to downwind nonattainment depend on the extent of the
nonattainment problem in the downwind area, the emissions in the
downwind area, the emissions in the upwind State, the distance between
the upwind State and the downwind area, and weather conditions (i.e.,
winds and temperatures which favor ozone formation and transport).
Because these factors vary in a complex way across the OTAG region, it
is not possible to develop a single bright line test for significance
that will be applicable and appropriate for all potential upwind-State-
to-downwind-area linkages. Therefore, EPA believes that it is more
appropriate to use a weight-of-evidence approach to account for all of
these factors than establishing a bright line criterion.
Comment: Some commented that EPA should not use the trajectory,
wind vector, and ``ozone cloud'' analyses as a

[[Page 57384]]

basis for determining significant contribution because these techniques
indicate air movement and do not account for ozone formation and
depletion due to photochemical reactions and other processes. Other
commenters argued in favor of using this information as means of
linking upwind States with downwind nonattainment.
Response: The EPA agrees that information from such techniques
should not be used as the sole basis for finding that certain upwind
States significantly contribute to nonattainment in specific downwind
States. However, EPA believes that it is important to consider the
``movement'' of ozone and/or precursors as part of the air quality
evaluation of contributions from upwind States. This factor is
incorporated into the air quality models used by EPA for this
rulemaking. The inclusion of this information, in conjunction with
numerous other air quality factors in the models, provides for a more
technically robust analysis than can be provided by the trajectory,
ozone cloud, and wind vector analyses alone.
Comment: A number of commenters stated that CAA section
110(a)(2)(D) requires a State-by-State demonstration that emissions
within an upwind State make a significant contribution to nonattainment
in another State and thus, EPA's proposed approach of using subregional
(i.e., multistate) modeling, together with each upwind State's
NO_X emissions, to establish these linkages is legally
flawed. These commenters argued that section 110(a)(2)(D) requires
``each implementation plan submitted by a State'' to contain provisions
that prohibit any source or other type of emissions activity ``within
the State'' from emitting air pollutants in amounts that contribute
significantly to a downwind nonattainment problem. The commenters
concluded that these provisions require, as a matter of technical
procedure, that EPA must base its determination that emissions from a
particular State significantly contribute to nonattainment downwind on
a technical analysis of that particular State's emissions. According to
the commenters, section 110(a)(2)(D) by its terms, prohibits EPA from
making that technical determination by examining the impact of
emissions from a group of States on a downwind nonattainment problem,
and then extrapolating from that information to determine whether
emissions from each State within that group should be considered to
make a significant contribution.
As a technical matter, these commenters argue that if emissions
from more than one State are lumped together in assessing the
contribution to a downwind State, there is no way to determine the
amount of emissions in each contributing State that must be reduced.
The commenters argue that the only way to establish specific upwind
State to downwind State linkages is through air quality modeling on a
State-by-State basis. Further, the commenters contend that once an area
beyond a particular State's boundaries is modeled, there is no way of
knowing how much farther upwind to go in terms of defining a source
area. In order to address these issues, many commenters stated that EPA
must do State-by-State zero-out UAM-V modeling and/or State-by-State
source apportionment modeling using the CAMx model to determine
downwind contributions from upwind States.
Response: On the legal issue, EPA disagrees that the above-
referenced provisions of section 110(a)(2)(D), by their terms, mandate
the technical procedure for EPA to make the determination of
significant contribution. These provisions simply indicate that EPA
must make that determination on a SIP-by-SIP basis, that is, for EPA to
issue a SIP call with respect to a particular State, EPA must determine
that the provisions of that SIP fail to adequately control emissions
from sources within the State. However, these provisions do not mandate
any particular technical procedure for making that determination. As a
result, EPA may employ any technical procedure that is sufficiently
accurate. As discussed below, EPA believes that its subregional
approach is sufficiently accurate to justify the SIP call. However, in
response to this and other comments, EPA did conduct State-by-State
modeling. The results of this modeling, as discussed below, confirm the
results of the subregional modeling.
On the technical issue, EPA used the subregional modeling as part
of the proposed approach because OTAG had developed and relied on this
modeling as part of its analysis to quantify the impacts of manmade
emissions in upwind areas on ozone in downwind areas. In addition, in
conjunction with other information, EPA believes that it is possible to
make rational extrapolations from the subregional results in order to
draw conclusions as to the contribution of individual States. The EPA
believes that it is credible to use NO_X emissions in each
State, along with the subregional modeling results, in the
determination of significance in view of the results of OTAG modeling
which indicate that, in addition to local emissions, the level of ozone
in a downwind State is directly related to the magnitude of
NO_X emissions in upwind areas and the proximity of the
upwind area to the downwind State. A more detailed discussion of the
technical validity of the subregional modeling is contained in the
Response to Comment Document.
The EPA recognizes that State-by-State modeling would provide some
additional precision to the magnitude and frequency of individual
State-to-State contributions. In response to the recommendations for
additional modeling, EPA performed both State-by-State UAM-V zero-out
modeling and State-by-State CAMx source apportionment modeling for many
of the upwind States in the OTAG region which were proposed as
significant contributors. The EPA's analysis of the contributions to
downwind nonattainment using the State-by-State modeling confirms the
overall finding, based on the proposed subregional modeling, that the
23 jurisdictions identified in the proposal significantly contribute to
nonattainment in downwind States. Specifically, the subregional
modeling indicates that manmade emissions from sources in subregions 1
through 9 make large and/or frequent contributions to 1-hour and 8-hour
nonattainment in specific downwind States. The EPA's analysis of the
State-by-State modeling demonstrates that each of the 23 upwind
jurisdictions identified through subregional modeling significantly
contribute to nonattainment in specific downwind States. In addition,
the results of the State-by-State modeling show that the specific
upwind-State-to-downwind-nonattainment linkages indicated by the
subregional modeling are confirmed overall by the State-by-State
modeling. The State-by-State modeling analyses are summarized below and
more fully documented in the Air Quality Modeling TSD.
Comment: The EPA received comments that zero-out modeling
introduces sharp spatial changes in emissions and pollutants along the
edges of the zero-out area. The commenters contend that this is not
credible and provides an incorrect assessment of transport.
Response: The EPA disagrees with this comment, as discussed in the
Response to Comments document. Also, as indicated above, in response to
other comments, EPA has performed CAMx source apportionment modeling
which does not use a zero-out technique for quantifying ozone
contributions from upwind States. In general, EPA has found that the
source apportionment technique and zero-out modeling

[[Page 57385]]

provide consistent information on the relative contribution of upwind
States to downwind nonattainment. In cases where the two techniques do
not provide consistent results, the source apportionment technique
tends to indicate larger contributions than the zero-out modeling. The
differences between these two modeling techniques are described further
in the Air Quality Modeling TSD.
Comment: Some comments referenced a study which analyzed the
``noise'' (i.e., uncertainty) in the UAM-V modeling system. This study
purports to show that the contributions from some States EPA proposed
as significant are within the ``noise'' of the model.
Response: This study focuses on model uncertainty by varying many,
but not all, inputs to the model. The study does not contend that the
inputs selected by OTAG are incorrect, but rather that there may be
other plausible values for these inputs. The results indicate that
there is a range of uncertainty in predicted ozone associated with the
range of possible values for the particular inputs studied by the
commenter. The study does not indicate that there is any bias in the
model's predictions (i.e., there is no indication that the predictions
are too high or too low). The specific values for the inputs being used
by EPA in its air quality modeling are the same values that were used
by OTAG. These values were selected by the OTAG Regional and Urban
Scale Modeling Work Group, which included experts in air quality
modeling from the public and private sector, in conjunction with the
model's developers, Systems Application International. The predictions
from OTAG's model runs using these same input values were evaluated
against ambient measurements and found by OTAG to provide acceptable
results. The EPA continues to believe that the specific inputs selected
by OTAG are technically sound and the modeling results are credible. A
further discussion of EPA's response to this comment is in the Response
to Comments document.
Comment: Several commenters stated that emissions from large point
sources of NO_X in specific States do not contribute
significantly to downwind nonattainment.
Response: As discussed in Section II.A.3.c, Definition of
Significant Contribution, under EPA's collective contribution approach,
if emissions in the aggregate from a particular geographic region or
State are found to contribute significantly to nonattainment downwind,
then the emissions in that region or State are considered to be
significant contributors to that nonattainment problem. Moreover, EPA
treats emissions as ``contributing significantly'' only to the extent
they may be eliminated through highly cost-effective reductions. Thus,
if all emissions from a State, when considered in the aggregate, are
found to contribute significantly to nonattainment downwind, and if
there are highly cost-effective controls for NO_X emissions
from sources in the upwind State, then the amount of NO_X
emissions from these sources that can be eliminated with such controls
are considered to be making a significant contribution. The amount of
emissions determined through this approach to make a significant
contribution may be relatively small, compared to the upwind State's
entire inventory; and the ambient impact downwind of eliminating that
amount may be relatively small as well. However, this small impact does
not mean that the emissions themselves are not significant insofar as
their contribution to nonattainment downwind. Further, as discussed in
Section IV, Air Quality Assessment, when the amount of emissions
required to be eliminated from upwind States are combined and modeled
collectively, their ambient impact downwind is larger.
Comment: One commenter provided a recommendation for dealing with
the concern that the spatial resolution of meteorological inputs to the
air quality model may be too coarse to require that predicted
exceedences correspond exactly with a county violating the NAAQS. The
commenter's recommendations were to base the selection of 1-hour
nonattainment receptors on model predicted exceedences in either (a)
all counties within the metropolitan statistical area containing the
nonattainment area or (b) all counties comprising the designated 1-hour
nonattainment area.
Response: The EPA believes that the appropriate way to address this
issue is to use all counties comprising the designated 1-hour
nonattainment area. That is, all counties in a designated 1-hour
nonattainment area should be considered as possible nonattainment
receptors for the purposes of evaluating contributions to nonattainment
under the 1-hour NAAQS. The EPA recognizes that not all counties within
a designated nonattainment area have monitors, and that some counties
may have monitors that indicate attainment in that county. Even so, EPA
recognizes that under the 1-hour NAAQS, nonattainment boundaries are
generally used to describe an area with the nonattainment problem.
Thus, EPA believes that this geographic vicinity offers the best
indication of an area that may be expected to have nonattainment air
quality somewhere within its boundaries. The EPA believes that it is
appropriate to include all counties in the designated nonattainment
area because the entire nonattainment area is responsible for meeting
the 1-hour NAAQS, even if only one monitor measures nonattainment at
any one time. As noted elsewhere, EPA predicts that many 1-hour
nonattainment areas that currently monitor nonattainment somewhere
within the area will remain in nonattainment in 2007, in some cases
because of predicted violations in counties that currently monitor
attainment. The EPA believes that the entire area should be considered
to be in nonattainment until all monitors in the area indicate
attainment of the NAAQS. Thus, in today's rulemaking, EPA used the
designated 1-hour nonattainment area in selecting the receptors to be
used to evaluate impacts on downwind nonattainment problems.
Comment: Several commenters questioned the validity of EPA's
approach of using the 3-episode average of the second highest 8-hour
daily maximum concentration to represent the form of the 8-hour NAAQS
(i.e., the 3-year average of the fourth highest 8-hour daily maximum
values at a monitor ³⁵). Commenters expressed the concern
that the average second high may not be representative for all areas
across the OTAG domain. However, none of the commenters provided any
suggested alternatives to EPA's approach.
---------------------------------------------------------------------------

\35\ For the purposes of discussion in this Section, these
values are referred to as ``design'' values.
---------------------------------------------------------------------------

Response: The analysis performed by EPA to establish a relationship
between the air quality during the OTAG episodes and the form of the 8-
hour NAAQS was based upon an analysis of 3 years of monitoring data
compared to monitoring data during the OTAG episodes. In response to
comments, EPA performed an analysis to determine how the predicted
average second high 8-hour values, as well as several alternative 8-
hour values, compared to ambient 8-hour design values, based on 1994 to
1996 measured data. Based on this analysis, EPA determined that,
overall, the model-predicted average second high values underestimate
the corresponding ambient design values for those counties in the OTAG
domain with 1994-1996 ambient values >=85 ppb. In addition to the
average second high, EPA also compared six other measures of 8-hour
model predictions to ambient design values. The six other measures
include the highest, second

[[Page 57386]]

highest, third highest, and fourth highest ozone predictions across the
July 1991, 1993, and 1995 episodes; the 3-episode average of the
highest concentrations; and the 3-episode average of the highest,
second highest, and third highest concentrations. The EPA also
developed the same measures using model predictions from all 4 episodes
for comparison to the ambient design values. The results indicate that
none of the alternative measures provides a universal best match to
ambient 8-hour design values in all States. Each of the indicators
overestimates values in some areas and underestimates values in other
areas to a varying extent. Furthermore, the best representation of 8-
hour design values using predictions from the OTAG episodes varies from
State to State. Given that the predicted average second high
underestimates ambient 8-hour design values and that none of the other
8-hour indicators examined by EPA provides a ``best'' match to ambient
values in all cases, EPA has decided to analyze the contributions to 8-
hour nonattainment problems using all 8-hour predictions >=85 ppb. The
EPA believes that this approach is appropriate given that EPA is using
modeling results for the 8-hour NAAQS merely as an indicator of the
likelihood that areas that currently monitor violations of the 8-hour
NAAQS will continue to be nonattainment for the 8-hour NAAQS and/or
have 8-hour maintenance problems in 2007.³⁶ Thus, the air
quality analysis of 8-hour contributions, described below, focuses on
all 8-hour values >=85 ppb.
---------------------------------------------------------------------------

\36\ Similarly, the EPA is also using 1-hour model predictions
>=125 ppb as an indicator that areas currently designated
nonattainment for the 1-hour NAAQS will continue to be nonattainment
for the 1-hour NAAQS in 2007.
---------------------------------------------------------------------------

Comment: Several commenters submitted new State-by-State zero-out
modeling using UAM-V and CAM_X source apportionment modeling
purporting to show that contributions from particular upwind States are
insignificant.
Response: The EPA reviewed the commenters' modeling to determine
and assess (a) the technical aspects of the models that were applied;
(b) the types of episodes modeled; (c) the methods for aggregating,
analyzing, and presenting the results; (d) the completeness and
applicability of the information provided; and (e) whether the
technical evidence supports the arguments made by the commenters.
Overall, the modeling submitted by commenters is viewed by EPA as
generally technically credible, although not complete in all cases. The
EPA's ability to fully evaluate and utilize the modeling submitted by
commenters was hampered in some cases because only limited information
on the results was provided. For example, a commenter may have provided
results for only 1 or 2 days in an episode, or for only one of several
episodes with no information presented on the results for the remaining
days or episodes that were modeled. As another example, results were
presented for only the peak ozone day in an episode while greater
contributions may have been predicted on other high ozone days of the
episode. For some of the modeling, the information was only presented
in graphical form which made the results difficult to evaluate in a
quantitative way. Also, in some cases the model predictions were only
presented as episode composite values without information on peak
contributions. The EPA's full assessment of the modeling submitted by
commenters is provided in the Response to Comments document.
In light of the absence of complete information in the modeling
provided by commenters and other comments calling for State-by-State
analyses, EPA decided to perform additional air quality modeling of the
type submitted by commenters in order to consider all of the data
resulting from such model runs. The EPA modeling includes State-by-
State zero-out modeling using UAM-V and State-by-State CAM_X
source apportionment modeling.
EPA conducted further analysis of other factors included in the
multi-factor approach for significant contribution. The results of
EPA's consideration of these factors and EPA's modeling are described
next.
3. Analysis of State-specific Air Quality Factors
a. Overall Nature of Ozone Problem (``Collective Contribution'').
As described above, EPA believes that each ozone nonattainment problem
at issue in today's rulemaking is the result of emissions from numerous
sources over a broad geographic area. The contribution from sources in
an upwind State must be evaluated in this context. This ``collective
contribution'' nature of the ozone problem supports the proposition
that the solution to the problem lies in a range of controls covering
sources in a broad area, including upwind sources that cause a
substantial portion of the ozone problem. This upwind share is
typically caused by NOx emissions from sources in numerous States.
States adjacent to the State with the nonattainment problem generally
make the largest contribution, but States further upwind, collectively,
make a contribution that constitutes a large percentage in the context
of the overall problem. As an example to illustrate the overall nature
of the ozone problem, EPA discusses below the ozone problem in the New
York City nonattainment area.
b. Extent of Downwind Nonattainment Problems. For each downwind
area to which an upwind State may be linked, EPA also examined the
extent of the downwind nonattainment problem, including the air quality
impacts of controls required in downwind areas under the CAA, as well
as of controls required or implemented on a national basis. As
indicated elsewhere, EPA determined that a downwind area should be
considered ``nonattainment'' for purposes of section 110(a)(2)(D)(i)(I)
under the 1-hour NAAQS if the area currently (as of the 1994-96 time
period) has nonattainment air quality ³⁷ and if the area is
modeled to have nonattainment air quality in the year 2007, after
implementation of all measures specifically required of the area under
the CAA as well as implementation of Federal measures required or
expected to be implemented by that date. The EPA determined that each
such downwind area had a residual nonattainment problem even after
implementation of all these control measures. The presence of residual
nonattainment is a factor that supports the need to reduce emissions
from upwind sources to allow further progress towards
attainment.³⁸ As an example, the residual nonattainment for
the New York City area is discussed in more detail below.
---------------------------------------------------------------------------

\37\ As explained elsewhere, for the 1-hour standard, EPA based
its determination as to the boundaries of the area with air quality
violating the NAAQS on the boundaries of the area designated as
nonattainment.
\38\ Indeed, the modeling relied on in today's action indicates
that many downwind nonattainment areas carry a residual
nonattainment problem even after implementation of regional
reductions by all the States affected by today's action. Although
not essential to EPA's conclusions, the presence of this
nonattainment problem even after implementation of regional
controls, based on the modeling used in today's rulemaking,
indicates that even further reductions, regionally or locally, would
be needed to assure attainment in those downwind areas.

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[[Page 57387]]

c. Air Quality Impacts of Upwind Emissions on Downwind
Nonattainment. As indicated above, in response to comments, additional
air quality modeling was performed by EPA to confirm the proposed
approach which relied on subregional modeling to quantify the impacts
of emissions from upwind States on nonattainment in downwind areas. The
additional modeling consisted of State-by-State zero-out modeling using
UAM-V and State-by-State source apportionment modeling using the CAMx
Anthropogenic Precursor Culpability Assessment (APCA)
technique.³⁹ A description of these models is contained in
the Air Quality Modeling TSD. Both models are currently being used by
the scientific and regulatory community for air quality assessments.
The EPA is not aware of any information that would indicate that either
model provides more credible predictions than the other. Each modeling
technique (i.e., zero-out and source apportionment) provides a
different technical approach to quantifying the downwind impact of
emissions in upwind States. The zero-out modeling analysis provides an
estimate of downwind impacts by comparing the model predictions from a
Base Case run to the predictions from a run in which the Base Case
manmade emissions are removed from a specific State. In contrast, the
source apportionment modeling quantifies downwind impacts by tracking
formation, chemical transformation, depletion, and transport of ozone
formed from emissions in an upwind source area and the impacts that
ozone has on nonattainment in downwind areas. The EPA ran both models
for all four OTAG episodes (i.e., July 1-11, 1988; July 13-21, 1991;
July 20-30, 1993; and July 7-18, 1995) using the 2007 SIP Call Base
Case emissions. The development of emissions for this Base Case
scenario are described in Section IV, Air Quality Assessment.
---------------------------------------------------------------------------

\39\ For ease of discussion, EPA is using the term ``UAM-V'' to
refer to the UAM-V State-by-State zero-out modeling and the term
``CAMx'' to refer to the CAMx source apportionment modeling.
---------------------------------------------------------------------------

The EPA selected several metrics in order to evaluate the downwind
contributions from emissions in upwind States. The metrics were
designed to provide information on the three fundamental factors for
evaluating whether emissions in an upwind State make large and/or
frequent contributions to downwind nonattainment. These factors are (a)
the magnitude of the contribution, (b) the frequency of the
contribution, and (c) the relative amount of the contribution. The
magnitude of contribution factor refers to the actual amount of
``ppbs'' of ozone contributed by emissions in the upwind State to
nonattainment in the downwind area. The frequency of the contribution
refers to how often the contributions occur and how extensive the
contributions are in terms of the number of grids in the downwind area
that are affected by emissions in the upwind State. The relative amount
of the contribution is used to compare the total ``ppb'' contributed by
the upwind State to the total ``ppb'' of nonattainment in the downwind
area.
As indicated above, two modeling techniques (i.e., UAM-V zero-out
and CAMx source apportionment) were used for the State-by-State
evaluation of contributions. The EPA developed metrics for both
modeling techniques for each of the three factors. However, because of
the differences between the two techniques, some of the metrics used
for the UAM-V modeling and the CAMx modeling are different. The
specific UAM-V and CAMx metrics and how they relate to the three
factors used for the evaluation of contributions are described below.
The EPA examined the contributions from upwind States to downwind
nonattainment for several types of nonattainment receptors.
Nonattainment receptors for the 1-hour analysis include those grid
cells that (a) are associated with counties designated as nonattainment
for the 1-hour NAAQS and (b) have 1-hour Base Case model predictions
>=125 ppb. These grid cells are referred to as ``designated plus
modeled'' nonattainment receptors. Using these receptors, the metrics
were calculated for each 1-hour nonattainment area as well as for each
State. To calculate the metrics by State, all of the 1-hour
nonattainment receptors in that State were pooled
together.⁴⁰ Table II-1 lists the 1-hour nonattainment areas
that were considered in this analysis, along with the State(s) in which
the nonattainment area is located. In addition to the areas listed in
Table II-1, EPA also evaluated the contributions of upwind States to
ozone concentrations over Lake Michigan because modeled air quality
over the lake can be indicative, under certain weather conditions, of
air quality in portions of the States surrounding the
lake.⁴¹
---------------------------------------------------------------------------

\40\ For ease of discussion in this Section, the 1-hour
nonattainment areas and the set of nonattainment receptors pooled
over an entire State are referred to as downwind areas.
\41\ High measured ozone concentrations in portions of Illinois,
Indiana, Michigan, and Wisconsin near the shoreline of Lake Michigan
are often associated with weather conditions which cause ozone
precursor pollutants to be blown offshore over the lake during the
morning, where they can form high ozone concentrations which then
return onshore during ``lake breeze'' wind flows in the afternoon.
Because the size of the grid cells used in the OTAG modeling is
relatively large compared to the spatial scale of the lake breeze,
the high ozone concentrations predicted over the lake may not be
blown back onshore in the model. Since high concentrations over the
lake do, in reality, impact air quality along the shoreline of one
or more of these States, the EPA believes that it is appropriate to
use predicted contributions to ozone over Lake Michigan as a
surrogate for contributions to any one of the surrounding States
(i.e., Illinois, Indiana, Michigan, and Wisconsin).

Table II-1.--1-Hour Nonattainment Areas Evaluated
------------------------------------------------------------------------
Nonattainment area State(s)
------------------------------------------------------------------------
Atlanta...................... Georgia.
Baltimore.................... Maryland.
Birmingham................... Alabama.
Boston/Portsmouth 1.......... Massachusetts, New Hampshire.
Chicago/Milwaukee ².......... Illinois, Indiana, Wisconsin.
Cincinnati................... Kentucky, Ohio.
Greater Connecticut.......... Connecticut.
Louisville................... Indiana, Kentucky.
Memphis...................... Mississippi, Tennessee.
New York City................ Connecticut, New Jersey, New York.
Philadelphia................. Delaware, Maryland, New Jersey,
Pennsylvania.
Pittsburgh................... Pennsylvania.
Portland..................... Maine.
Rhode Island................. Rhode Island.
Southwestern Michigan ³...... Michigan.

[[Page 57388]]

St. Louis.................... Illinois, Missouri.
Washington, DC............... District of Columbia, Maryland, Virginia.
Western Massachusetts........ Massachusetts.
------------------------------------------------------------------------
\1\ For the purposes of this analysis EPA has combined the Greater
Boston nonattainment area which includes portions of Massachusetts and
New Hampshire, with the Portsmouth, New Hampshire nonattainment area
into a single downwind nonattainment receptor area.
\2\ For the purposes of this analysis EPA has combined the 1-hour
nonattainment counties that are along the shoreline of Lake Michigan
in the States of Illinois, Indiana, and Wisconsin into a single
downwind nonattainment receptor area.
\3\ For the purposes of this analysis EPA has combined the 1-hour
nonattainment counties that are along the shoreline of Lake Michigan
in the State of Michigan into a single downwind nonattainment receptor
area.

For the 8-hour analysis, nonattainment receptors are those grid
cells that (a) are associated with counties currently violating the 8-
hour NAAQS (based on 1994-1996 data) and (b) have 8-hour Base Case
model predictions >=85 ppb. These grid cells are referred to as
``violating plus modeled'' nonattainment receptors. The metrics for the
8-hour contribution analyses were calculated on a State-by-State basis
by pooling together the ``violating plus modeled'' receptors in a
State.
(1) UAM-V State-by-State Modeling. In the UAM-V zero-out model runs
all manmade emissions in a given upwind State were removed from the
Base Case scenario. Each zero-out scenario was run for all 4 episodes
and the ozone predictions in downwind States were then compared to
those from the Base Case run in order to quantify the downwind impacts
of emissions from the upwind State (i.e., the State in which the
manmade emissions were removed). The EPA performed zero-out runs for
the following set of States:
. Alabama, Georgia, Illinois, Indiana, Kentucky,
Massachusetts, Michigan, Missouri, North Carolina, Ohio, South
Carolina, Tennessee, Virginia, West Virginia, and Wisconsin.
Zero-out modeling for Massachusetts was performed because this
State was the only State in the Northeast with relatively large
NO_X emissions that was not included in any of the OTAG
subregional modeling. The other States listed above were selected for
zero-out modeling in order to respond to comments that emissions in all
or portions of each of these States do not contribute significantly to
downwind nonattainment.
The EPA analyzed the model-predicted ozone concentrations from the
zero-out runs using the four metrics described below. The results for
these metrics are too voluminous to include in the notice in their
entirety. The full set of results is contained in the Air Quality
Modeling TSD. Each metric was calculated using 1-hour daily maximum
concentrations >=125 ppb as well as 8-hour daily maximum concentrations
>=85 ppb. Model predictions from all 4 episodes were used for
calculating the metrics.⁴²
---------------------------------------------------------------------------

\42\ Model predictions from the first few days of each episode
are considered ``ramp-up'' days and were excluded from the analysis,
following the procedures adopted by OTAG. The ramp-up days include
the first 3 days of the July 1988, 1991, and 1995 episodes and the
first 2 days of the July 1993 episode.
---------------------------------------------------------------------------

UAM-V Metric 1: Exceedences. This metric is the total number of
predicted concentrations exceeding the NAAQS (i.e. 1-hour values >=125
ppb and 8-hour values >=85 ppb) within the downwind area. In
calculating this metric, EPA summed the number of occurrences of values
above the applicable standard (i.e., 1-hour or 8-hour) for all
nonattainment receptors within the downwind area. For example, in
Downwind Area #1 there are five 1-hour ``designated plus modeled''
nonattainment receptors. For this downwind area, the Base Case value
for Metric 1 is calculated by first counting the number of days, across
all four episodes, that had 1-hour daily maximum values >=125 ppb at
each of the five receptors. The result is the total number of
exceedences at each receptor over all days in all four episodes. The
total number of exceedences at each receptor is then summed across all
five receptors to produce the total number of exceedences in Downwind
Area #1, which is the value for Metric 1 for this area.
UAM-V Metric 2: Ozone Reduced--ppb. This metric shows the magnitude
and frequency of the ``ppb'' impacts from each upwind State on ozone
concentrations in each downwind area. These impacts are quantified by
calculating the difference in ozone concentrations between the zero-out
run and the Base Case. The results are then tabulated in terms of the
number of ``impacts'' within six concentration ranges: >=2 to 5 ppb,
>=5 to 10, >=10 to 15, >=15 to 20, >=20 to 25, and >=25 ppb. The
impacts for 1-hour daily maximum values and 8-hour daily maximum values
are determined by tallying the total ``number of days and grid cells''
>=125 ppb or >=85 ppb that receive contributions within the
concentration ranges. In the analysis of contributions, as described
below, the data from Metric 2 are used in conjunction with Metric 1 to
determine the percent of the exceedences in the downwind area that
receive contributions of >=2 ppb, >= 5 ppb, >=10, ppb, etc. The maximum
``ppb'' impact within the downwind area is also calculated.
UAM-V Metric 3: Total ppb Reduced. This metric quantifies the total
ppb contributed in the downwind area from an upwind State, not
including that portion of the contribution that occurs below the level
of the NAAQS. For 1-hour concentrations, Metric 3 is calculated by
taking the difference between the Base Case predictions in each
nonattainment receptor and either (a) the corresponding value in the
zero-out run, or (b) 125 ppb, whichever is greater (i.e., 125 ppb or
the prediction in the zero-out run). The Base Case vs. zero-out
differences are summed over all days and across all nonattainment
receptors in the downwind area. The calculation of this metric is
illustrated by the following example. If the Base Case 1-hour daily
maximum ozone prediction is 150 ppb and the corresponding value from
the zero-out run is 130 ppb, then the difference used in this metric is
20 ppb. However, if the value from the zero-out run is 115 ppb, then
the difference used in this metric is 25 ppb (i.e., 150 ppb-125 ppb,
because 115 ppb is less than 125 ppb).
For analyzing the contributions using Metric 3, the values of this
metric are compared to the total amount of ozone above the NAAQS (i.e.,
125 ppb, 1-hour or 85 ppb, 8-hour) in the Base Case. This baseline
measure of the ``total amount of nonattainment'' (i.e., the total
``ppb'' of ozone that is above the NAAQS) is calculated by summing the
``ppb'' values in the Base Case that are above the level of the NAAQS.
The total contribution from an upwind State to a particular downwind
area calculated by Metric 3 is expressed in relation to the

[[Page 57389]]

amount that the downwind area is in nonattainment. For example, if
Upwind State #1 contributes a total of 50 ppb >=125 ppb to Downwind
Area #2 and the total Base Case ozone >=125 ppb in Downwind Area #2 is
500 ppb, then the contribution from Upwind State #1 (i.e., 50 ppb) to
Downwind Area #2 is equivalent to 10 percent of Downwind Area #2's
nonattainment problem (i.e., 50 ppb divided by 500 ppb, times 100).
UAM-V Metric 4: Population-Weighted Total ppb Reduced. This metric
is similar to the ``Total ppb Reduced'' metric except that the
calculated contributions are weighted by (i.e., multiplied by)
population. In calculating this metric, the ``ppb'' contributions are
determined for each nonattainment receptor, then summed across all
nonattainment receptors in a particular downwind area. During this
calculation, the population in the nonattainment receptor is multiplied
by the total contribution in that receptor (i.e., grid cell) and then
this value is added to the corresponding values for the other receptors
in the downwind area. The results for this metric are expressed
relative to the population-weighted Base Case amount similar to the
approach followed with Metric 3, as described above.
(2) CAMx Source Apportionment Modeling. In the CAMx modeling, the
source apportionment technique was used to calculate the contributions
from upwind States to ozone concentrations above the NAAQS in downwind
areas. Due to computational constraints, it was not possible for EPA to
treat each State in the OTAG region as a separate source area. Several
of the smaller States in the Northeast were grouped together as were
seven States in the far western portion of the region. The following
States were treated as individual source areas:
. Alabama, Florida, Georgia, Illinois, Indiana, Iowa,
Kentucky, Louisiana, Maine, Massachusetts, Michigan, Mississippi,
Missouri, New Jersey, New York, North Carolina, Ohio, Pennsylvania,
South Carolina, Tennessee, Texas, Virginia, West Virginia, and Wisconsin.
The following States were grouped together:
. Connecticut and Rhode Island were combined; Maryland,
Delaware and the District of Columbia were combined; New Hampshire and
Vermont were combined; and Arkansas was combined with the portions of
Oklahoma, Kansas, Minnesota, Nebraska, North Dakota, and South Dakota
that lie within the OTAG region.
The contributions from each of these source areas to downwind
nonattainment were evaluated using four metrics. As indicated above,
the CAMx metrics are calculated for the same types of nonattainment
receptors as the UAM-V zero-out metrics. The CAMx metrics are
calculated in a way that is different from the metrics used for the
zero-out runs in large part because of the differences between the two
techniques. The zero-out modeling calculates contributions using the
difference in predictions between two model runs (i.e., a Base Case and
a State-specific zero-out run). In contrast, the CAMx source
apportionment technique calculates contributions by internally tracking
ozone formed from emissions in each source area. In raw form, the
source apportionment technique produces a ``ppb'' contribution from
each source area to hourly ozone in each receptor grid cell. The
individual hourly ``ppb'' contributions were treated in the way
described below to calculate 1-hour and 8-hour values for the four
metrics. The approach was based on recommendations to EPA by Environ,
the developers of CAMx. For 1-hour concentrations the metrics are
calculated based on contributions to all hourly predictions >=125 ppb.
For 8-hour concentrations, the metrics are calculated based on the
contribution to every 8-hour period in a day with an average
concentration >=85 ppb. In order to provide a link to the way 1-hour
and 8-hour concentrations were treated for the zero-out runs, EPA also
calculated the CAMx metrics for 1-hour daily maximum values >=125 ppb
and 8-hour daily maximum values >=85 ppb. ⁴³ The full set of
results for all of the CAMx metrics is contained in the Air Quality
Modeling TSD.
---------------------------------------------------------------------------

\43\ As described in the Air Quality Modeling TSD, the metrics
calculated using the hourly contributions >= 125 ppb are consistent
with the metrics calculated using 1-hour daily maximum contributions
>= 125 ppb. Similarly, the metrics calculated using all 8-hour
periods >= 85 ppb are consistent with the metrics calculated using
8-hour daily maximum values >= 85 ppb.
---------------------------------------------------------------------------

The CAMx Metrics 1 and 2 provide information on the magnitude and
frequency of contributions in a form that is similar to UAM-V Metrics 1
and 2.
CAMx Metric 3: Highest Daily Average Contribution. This metric is
the highest daily average ozone ``ppb'' contribution from each upwind
source area to each downwind nonattainment receptor area over all days
modeled in all four episodes. The following example illustrates how
this metric is calculated for 1-hour ozone concentrations. Similar
procedures are followed for calculating this metric for 8-hour
concentrations. First, the hourly ``ppb'' contributions from a
particular upwind source area to each nonattainment receptor in a
downwind area are summed across all receptors in the downwind area.
This total daily contribution is then divided by the number of hours
and grid cells >=125 ppb in the downwind area to determine the daily
average ``ppb'' contribution. This calculation is performed on a day by
day basis for each day in the 4 episodes. After the average
contributions are calculated for each day, the highest daily average
value across all episodes is selected for analysis. In addition, the
highest daily average contribution is expressed as a percent of the
downwind area's average ozone >=125 ppb. That is, the highest daily
average ``ppb'' contribution is divided by the average of the ozone
concentrations >=125 ppb on that day (i.e., the day on which the
highest average ppb contribution occurred). For example, if the highest
daily average contribution from an upwind State to nonattainment
downwind is 15 ppb and the average of the hourly ozone values >=125 ppb
on this day in the downwind area is 150 ppb, then the 15 ppb
contribution, expressed as a percent, is 10 percent.
CAMx Metric 4: Percent of Total Manmade Ozone Contribution. This
metric represents the total contribution from emissions in an upwind
State relative to the total ozone for all hours above the NAAQS in the
downwind area. This metric, which is referred to as the ``average
contribution,'' is calculated for each episode as well as for all four
episodes combined. The following example is used to illustrate how this
metric is calculated for a single episode for a particular downwind
area. In step 1, all predicted Base Case hourly values >=125 ppb in the
downwind area are summed over all nonattainment receptors and all days
in an episode. In step 2, the ``ppb'' contributions from a source area
to this downwind area are summed over all nonattainment receptors in
the downwind area and all days in the episode to yield a total ppb
contribution. The total contribution calculated in Step 2 is then
divided by the total ozone >=125 ppb in the downwind area to produce
the fraction of ozone >=125 ppb in the downwind area that is due to
emissions from the upwind source area. This fraction is multiplied by
100 to express the result as a percent.
4. Confirmation of States Making a Significant Contribution to Downwind
Nonattainment
In the proposal, EPA made findings of significant contribution
based on a

[[Page 57390]]

weight-of-evidence approach that included consideration of air quality
contributions based on subregional modeling. As discussed in section
II.C.2, Summary of Notice of Proposed Rulemaking Weight-of-Evidence
Approach, EPA believes that the subregional modeling provides an
adequate independent basis for determining which States contribute
significantly to downwind nonattainment. The evaluation of the State-
by-State modeling confirms the overall findings that were based on the
subregional modeling and provides more refined information regarding
the impacts of specific upwind States on nonattainment in individual
downwind areas. This State-by-State modeling is discussed in more
detail below.
a. Analysis Approach. The EPA has analyzed the results of the
State-by-State UAM-V zero-out modeling and the State-by-State CAMx
source apportionment modeling for each of the 23 jurisdictions for
which this modeling is available.⁴⁴ Both UAM-V and CAMx
modeling results are available for fifteen States (i.e., Alabama,
Georgia, Illinois, Indiana, Kentucky, Massachusetts, Michigan,
Missouri, North Carolina, Ohio, South Carolina, Tennessee, Virginia,
West Virginia, and Wisconsin). For an additional eight States (i.e.,
Connecticut, Delaware, the District of Columbia, Maryland, New Jersey,
New York, Pennsylvania, and Rhode Island), CAMx modeling is available.
Also, as noted above in Section II.C.3, State-by-State Air Quality
Modeling, Connecticut and Rhode Island were combined as a single source
area, and Maryland, the District of Columbia, and Delaware were also
combined as a single source area. Because the NO_X emissions
and/or NO_X emissions density is large in each jurisdiction
within both of these combined source areas, EPA believes that the
downwind contributions from these combined source areas can be
attributed to each jurisdiction within the source area.
---------------------------------------------------------------------------

\44\ The approach for dealing with the 15 States in the OTAG
domain which were not proposed to make a significant contribution to
downwind nonattainment are discussed below in Section II.C.5, States
Not Covered by this Rulemaking.
---------------------------------------------------------------------------

For the 1-hour NAAQS, EPA evaluated downwind impacts in two ways
using the factors described in Section II.C.3, State-by-State Air
Quality Modeling. First, EPA evaluated the contributions from each
upwind State to nonattainment in each downwind State. Second, the EPA
evaluated the contributions from each upwind State to nonattainment in
each downwind 1-hour nonattainment area. In downwind States which only
contain a single intrastate nonattainment area (e.g., Atlanta), the
results of the downwind State and downwind nonattainment area analyses
are the same because the same nonattainment receptors are used in both
cases. For the 8-hour NAAQS, EPA evaluated the contributions from
upwind States to 8-hour nonattainment in each downwind State.
The EPA used the following process in determining whether a
particular upwind State contributes significantly to 1-hour
nonattainment in an individual downwind area. First, EPA reviewed the
extent of the nonattainment problem in the downwind area using ambient
design values and model predictions of future ozone concentrations
after the application of (a) 2007 Base Case controls, (b) additional
local NO_X reductions, and (c) regional reductions
(additional local plus upwind NO_X reductions).⁴⁵
As indicated above, EPA determined that each downwind area had a
residual nonattainment problem even after implementation of the control
measures in the 2007 Base Case.
---------------------------------------------------------------------------

\45\ Scenarios (b) and (c) refer to the runs used to assess
transport as described in Section IV.
---------------------------------------------------------------------------

Second, using the information from CAMx Metric 4 ⁴⁶, EPA
reviewed (a) the relative portion of the ozone problem in each downwind
area that is due to ``local'' emissions (i.e., emissions from the
entire State or States in which the downwind area is located), (b) the
total contribution from all upwind emissions (i.e., the sum of the
contributions from manmade emissions in all upwind States, combined),
and (c) the contribution from manmade emissions in individual upwind
States. The local versus upwind contributions for each downwind area
are provided in the Air Quality Modeling TSD. The EPA analyzed this
information to determine whether upwind emissions are an important part
of the downwind areas' nonattainment problem. In general, the data
indicate that, although a substantial portion of the 1-hour
nonattainment problem in many of the downwind areas is due to local
emissions, a substantial portion of the nonattainment problem is also
due to emissions from upwind States. In addition, for most upwind-
State-to-downwind-area linkages there is no single upwind State that
makes up all of the upwind contribution. Rather, the total contribution
for all upwind States combined is comprised of individual contributions
from a number of upwind States many of which are relatively similar in
magnitude such that there is no ``bright line'' which distinguishes
between the contributions from most of the individual upwind States.
---------------------------------------------------------------------------

\46\ This information represents the average contributions
across all four episodes. In addition to the four-episode average
contribution, EPA also examined the highest single-episode average
contribution from each upwind State to each downwind area.
---------------------------------------------------------------------------

Third, EPA determined whether each individual upwind State
significantly contributes to nonattainment in a particular downwind
area using the UAM-V and CAMx metrics to evaluate three aspects, or
factors of the contribution.⁴⁷ These factors include the
magnitude, frequency, and relative amount of the contribution. The
specific UAM-V and CAMx metrics which correspond to each of the factors
are identified in Table II-2. As indicated in the table, there is at
least one metric from each modeling technique that corresponds to each
of the three factors.
---------------------------------------------------------------------------

\47\ The factors used to interpret the metrics should not be
confused with the multi-factor approach used to identify the amounts
of NO_X emissions that contribute signficantly to
nonattainment.

Table II-2.--Metrics Associated With Each Contribution Factor
------------------------------------------------------------------------
Factor UAM-V CAMx
------------------------------------------------------------------------
Magnitude of Contribution... Maximum ``ppb'' Maximum ``ppb''
contribution Contribution
(Metric 2) (Metric 2); and
Highest Daily
Average
Contribution
(Metric 3).
Frequency of Contribution... Number and percent Number and percent
of exceedences with of exceedences with
contributions in contributions in
various various
concentration concentration
ranges (Metric 1 ranges (Metric 1
and 2) and 2).
Relative Amount of Total ``ppb'' Four-episode average
Contribution. contribution percent
relative to the contribution from
total ``ppb'' that the upwind State to
the downwind area nonattainment in
is above the NAAQS the downwind area
(Metric 3); and (Metric 4); and
Total population- Highest single-
weighted ``ppb'' episode average
contribution percent
relative to the contribution from
total population- the upwind State to
weighted ``ppb'' nonattainment in
that the downwind the downwind area
area is above the (Metric 4).
NAAQS (Metric 4)
------------------------------------------------------------------------

[[Page 57391]]

It should be noted that the relative contributions of individual
upwind States to a particular downwind area add up to 100 percent for
the CAMx 4-episode average percent contribution. However, this is not
the case for the CAMx highest single-episode average percent
contribution since the value from one upwind State can occur in a
different episode than the value from another upwind State for the same
downwind area. In addition, it should be noted that UAM-V Metrics 3 and
4 are used in combination to express the total contribution above the
NAAQS relative to the total amount that the downwind area is above the
NAAQS. The values for each of these metrics also do not add up to 100
percent when considering contributions from multiple upwind States to
an individual downwind area.
The EPA compiled the UAM-V and CAMx metrics by downwind area in
order to evaluate the contributions to downwind nonattainment. The data
on 1-hour and 8-hour contributions were compiled and analyzed
separately. The data were reviewed to determine how large of a
contribution a particular upwind State makes to nonattainment in each
downwind area in terms of the magnitude of the contribution and the
relative amount of the total contribution. The data were also examined
to determine how frequently the contributions occur.
The first step in evaluating this information was to screen out
linkages for which the contributions were very low, as described in the
Air Quality Modeling TSD. The finding of significance for linkages that
passed the initial screening criteria was based on EPA's technical
assessment of the values for the three contribution factors. Each
upwind State that had large and/or frequent contributions to the
downwind area, based on these factors, is considered as contributing
significantly to nonattainment in the downwind area. The EPA believes
that each of the factors provides an independent legitimate measure of
contribution. However, there had to be multiple factors that indicate
large and/or frequent contributions in order for the linkage to be
significant. In this regard, the finding of a significant contribution
for an individual linkage was not based on any single factor.
For many of the individual linkages the factors yield a consistent
result (i.e., either large and/or frequent contributions or small and/
or infrequent contributions). In some cases, however, not all of the
factors are consistent. For upwind-downwind linkages in which some of
the factors indicate high and/or frequent contributions while other
factors do not, EPA considered the overall number and magnitude of
those factors that indicate large and/or frequent contributions
compared to those factors that do not. Based on an assessment of all
the factors in such cases, EPA determined that the upwind State
contributes significantly to nonattainment in the downwind area if on
balance the factors indicate large and/or frequent contributions from
the upwind State to the downwind area.
The EPA's evaluation of the contributions to 1-hour nonattainment
in New York City is presented as an example to illustrate this process.
The New York City area, which consists of portions of New York, New
Jersey, and Connecticut, is designated as a severe nonattainment area
under the 1-hour NAAQS. The ambient 1-hour design value in New York
City, based on 1994 through 1996 monitoring data is 144 ppb. During the
four OTAG episodes, 39 percent of the days are predicted to have 1-hour
exceedences in 2007 after the implementation of all CAA controls and
Federal measures.⁴⁸ Moreover, EPA's air quality modeling of
the benefits of regional NO_X strategies, as described in
Section IV, Air Quality Assessment, indicates that there would still be
exceedences of the 1-hour NAAQS remaining in New York City even with
eliminating the significant amounts of emissions required by this
NO_X SIP Call.
---------------------------------------------------------------------------

\48\ This is further described in the Air Quality Modeling TSD.
---------------------------------------------------------------------------

In the assessment of contributions to New York City, EPA examined
the local versus upwind contributions to 1-hour nonattainment in this
area, as shown in Table II-3. Local emissions in the New York City
nonattainment area are spread among numerous stationary sources, area
sources, highway sources, and nonroad sources, each of which
contributes only a very small, indeed sometimes immeasurable, amount to
New York City's ozone nonattainment problem. Combined, these emissions
result in approximately 55 percent of the New York City area's ozone
problem. Emissions from States upwind of New York, New Jersey, and
Connecticut, on average across all four episodes, contribute 45 percent
of the nonattainment problem in New York City is due to. However, no
single State stands out as contributing most of the total upwind
contribution. The biggest single contributor is Pennsylvania (18
percent) followed by Maryland/Washington, DC/Delaware (5 percent). The
total contribution from all Northeast States is 23 percent. A similar
amount (22 percent) of the total contribution is due to emissions in
those States outside the Northeast. The data in Table II-3 indicate
that 19 percent of the 22 percent is fairly evenly divided among ten
States, whose contributions range from 1 percent (6 States) to 4
percent (Ohio and Virginia). The remaining 3 percent (i.e., 19 percent
vs 22 percent) is from States that each contribute less than 1 percent,
on average. The highest single-episode contributions from States upwind
of the Northeast range from 1 percent (Tennessee) to 8 percent
(Virginia). In general, the contribution data in Table II-3 indicate
that a substantial amount of New York City's nonattainment problem is
due to the collective contribution from emissions in a number of upwind
States both within and outside the northeast. That these upwind
contributions are a meaningful part of New York City's nonattainment
problem is particularly evident in light of the fact that the
contribution to the problem made by New York City itself is comprised
of the collective contribution of numerous sources.

Table II-3.--Percent Contribution From Upwind States to 1-Hour Nonattainment in New York City \1\
----------------------------------------------------------------------------------------------------------------
Percent of
total manmade Highest single-
Downwind area: New York City emissions over episode percent
4 episodes contribution
-------------------------------------------------------------------------------------------------------\2\------
Amount due to ``Local'' Emissions \3\.......................................... 55 \4\NA
Total Amount from all ``Upwind'' States........................................ 45 NA
Contributions from Individual Upwind States.................................... .............. ...............
PA............................................................................. 18 19
MD/DC/DE....................................................................... 5 6

[[Page 57392]]

OH............................................................................. 4 6
VA............................................................................. 4 8
WV............................................................................. 3 7
IL............................................................................. 2 3
IN............................................................................. 1 2
KY............................................................................. 1 3
MI............................................................................. 1 4
MO............................................................................. 1 2
NC............................................................................. 1 2
TN............................................................................. 1 1
Total Amount from All Other States, combined................................... 3 NA.
----------------------------------------------------------------------------------------------------------------
\1\ These values are based on CAMx Metric 3 calculated across all 4 episodes.
\2\ These values are based on CAMx Metric 3 calculated for each episode individually. These values do not add up
to 100 percent.
\3\ 3. Total contribution from the State(s) in which the Nonattainment area is located.
\4\ 4. Not applicable.

The extent of New York City's nonattainment problem and the nature
of the contributions from upwind States were considered in determining
whether the values of the metrics indicate large and/or frequent
contributions for individual upwind States. Specifically, additional
controls beyond the local and upwind NO_X reductions which
are part of the regional NO_X strategy may be needed to solve
New York City's 1-hour nonattainment problem. Also, the total
contribution from all upwind States is large and there is no single
State or small number of States which comprise this total upwind
portion. In this regard, the contributions to New York City from some
States may not appear to be individually ``high'' amounts. However, (as
described below) these contributions, when considered together with the
contributions from other States (i.e., the collective contribution)
produce a large total contribution to nonattainment in New York City.
The EPA evaluated the magnitude, frequency, and relative amount of
contribution from emissions in individual upwind States to determine
which States contribute significantly to 1-hour nonattainment in New
York City. The UAM-V and CAMx metrics which quantify each upwind
State's contribution to New York City for each of the three factors are
provided in the Air Quality Modeling TSD and described below.
Examination of the values for these metrics indicates that the upwind
States can be divided into three general groups, based on the
magnitude, frequency, and relative amount of contribution. The first
group contains those upwind States for which the UAM-V and CAMx metrics
all clearly indicate a significant contribution to 1-hour nonattainment
in New York City. The second group contains those States for which the
CAMx and UAM-V metrics are not quite as consistent, but overall the
metrics indicate a significant contribution to 1-hour nonattainment in
New York City.⁴⁹ The third group contains those States for
which the CAMx and UAM-V metrics clearly indicate that the impacts do
not make a significant contribution to New York City.
---------------------------------------------------------------------------

\49\ For New York City, each of the ``Group 2'' States were
found to make a significant contribution. However, this was not the
case for all of the Group 2 linkages in other nonattainment areas.
For example, the contribution from Kentucky to Philadelphia and the
contribution from Tennessee to Baltimore were Group 2 situations in
which EPA determined that the contributions were not significant.
---------------------------------------------------------------------------

Group 1 Upwind States:
The CAMx and UAM-V metrics all clearly indicate that emissions from
Maryland/Washington, DC/Delaware, Ohio, Pennsylvania, Virginia, and
West Virginia make large and/or frequent contributions to 1-hour
nonattainment in New York City. For Pennsylvania the magnitude of
contribution, as indicated by the highest daily average contribution
(CAMx Metric 3), is 25 ppb and the relative amount of contribution is
18 percent (CAMx Metric 4). For the other upwind areas, the magnitude
of the contributions range from 9 ppb to 15 ppb (CAMx Metric 3, highest
daily average contributions) with contributions in the range of 5 ppb
to 10 ppb--from Ohio, Virginia, and West Virginia (UAM-V Metric 2,
maximum ``ppb'' contribution). In terms of the frequency of the
contribution, 7 percent to 11 percent of the total number of grid-hours
>=125 ppb in New York City receive contributions of 10 ppb from each of
these States (CAMx Metric 1 and 2). Also, the relative amounts of the
contribution are in the range of 6 percent to 8 percent (CAMx Metric 4,
highest single-episode average percent contribution) and the total
contribution from each of three States (i.e., Ohio, Virginia, and West
Virginia) is large compared to the total amount of nonattainment,
ranging from 8 percent to 11 percent (UAM-V Metric 3).
Group 2 Upwind States:
The CAMx and UAM-V metrics are somewhat less consistent on the
extent of contributions from each of 5 States: Kentucky, Illinois,
Indiana, Michigan, and North Carolina. None of the metrics for either
model indicate extremely low or extremely high contributions. Rather,
for these States most of the metrics indicate relatively high
contributions while a few metrics indicate relatively low
contributions. The rationale used by EPA for evaluating the
contributions from these States involved comparing and contrasting each
piece of data for these States on an individual ``upwind State-by-
upwind State'' basis and as a group (i.e., for all 5 States, together)
in order to weigh the relative magnitude and frequency of the
contributions for making a determination of significance.
UAM-V Metrics--For each of these 5 States the ``weakest'' factor is
the magnitude contribution (UAM-V Metric 2) in that the highest
contributions are in the range of 2 to 5 ppb. The other UAM-V Metrics,
however, indicate that the contributions from each State are of a
larger frequency and relative amount. Specifically, four of these
States (Kentucky, Indiana, Illinois, and

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Michigan) each contribute 2 to 5 ppb to as many as 3 percent to 4
percent of the exceedences in New York City (UAM-V Metrics 1 and 2).
While North Carolina contributes to somewhat fewer exceedences (2
percent), this slight weakness is out-weighed by the relative amount of
contribution (UAM-V Metrics 3 and 4) which indicates that the total
contribution from North Carolina alone is equivalent to 3 percent of
the total ``ppb'' >=125 ppb and 4 percent of the population-weighted
``ppb'' >=125 ppb in New York City. For Indiana, Illinois, and Michigan
the relative amount of contribution (UAM-V Metrics 3 and 4) is also
relatively high and ranges from 3 percent to 5 percent. The relative
amount of contribution from Kentucky is somewhat weaker at 2 percent.
CAMx Metrics--For Illinois, all of the CAMx metrics indicate
relatively large and/or frequent contributions, as described below. For
Kentucky, Indiana, Michigan, and North Carolina the magnitude of
contribution is large, as indicated by the maximum contribution which
ranges from 6 ppb (Indiana) to 11 ppb (North Carolina). Also, the
highest daily average contribution from Kentucky, Michigan, and North
Carolina are all in the range of 5 ppb to 7 ppb. In terms of the
frequency of contribution, Indiana and North Carolina contribute in the
range of 5 ppb to 10 ppb to 3 percent and 6 percent of the exceedences,
respectively, in New York City. For Kentucky, Indiana, Michigan, and
North Carolina the relative amounts of contribution is somewhat mixed
in that the 4-episode average percent contribution is only 1 percent,
but the highest single-episode average percent contributions are higher
at 2 percent from both Indiana and North Carolina, 3 percent from
Kentucky, and 4 percent from Michigan (CAMx Metric 4).
Overall contributions considering UAM-V and CAMx Metrics--
Considering the CAMx and UAM-V metrics, as described below, the
majority of the contribution factors indicate that, overall, each of
the Group 2 States contributes significantly to 1-hour nonattainment in
New York City.
Kentucky--
Metrics indicating relatively high and/or frequent contributions:

--Magnitude of Contribution: the maximum contribution from CAMx is 9
ppb (CAMx Metric 2) and highest daily average contribution is 7 ppb
(CAMx Metric 3);
--Frequency of Contribution: 4 percent of the exceedences receive
contributions of more than 2 ppb (UAM-V Metrics 1 and 2); and
--Relative Amount of Contribution: the highest single-episode average
contribution is 3 percent (CAMx Metric 4).