National Air Toxics Program: The Integrated Urban Strategy
Related Material
[Federal Register: July 19, 1999 (Volume 64, Number 137)]
[Notices]
[Page 38705-38740]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr19jy99-135]
[[Page 38705]]
_______________________________________________________________________
Part II
Environmental Protection Agency
_______________________________________________________________________
National Air Toxics Program: The Integrated Urban Strategy; Notice
[[Page 38706]]
ENVIRONMENTAL PROTECTION AGENCY
[FRL-6376-7; Docket No. A-97-44]
National Air Toxics Program: The Integrated Urban Strategy
AGENCY: Environmental Protection Agency (EPA).
ACTION: Notice.
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SUMMARY: This document provides an overview of EPA's national effort to
reduce air toxics, including stationary and mobile source standards,
cumulative risk initiatives, assessment approaches, and education and
outreach. This national air toxics program includes activities under
multiple Clean Air Act (Act) authorities to reduce air toxics emissions
from all sources, including major industrial sources, smaller
stationary sources, and mobile sources such as cars and trucks. By
integrating activities under different parts of the Act, EPA can better
address cumulative public health risks and adverse environmental
impacts posed by exposures to multiple air toxics in areas where the
emissions and risks are most significant.
In addition, this document describes a new major component of our
national effort, the Integrated Urban Air Toxics Strategy (Strategy)
developed under the authority of sections 112(k) and 112(c)(3) of the
Act. The Strategy reflects the public comments received on the draft
Strategy, which was published on September 14, 1998 (63 FR 49240).
The Strategy includes a description of risk reduction goals; a list
of 33 hazardous air pollutants (HAPs) judged to pose the greatest
potential threat to public health in the largest number of urban areas,
including 30 HAPs specifically identified as being emitted from smaller
industrial sources known as ``area'' sources; and a list of area source
categories which emit a substantial portion of these HAPs, and which
are being considered for regulation under section 112(d). Because
mobile sources are an important contributor to the urban air toxics
problem, the Strategy also describes actions under Title II (including
section 202(l)) of the Act to reduce toxics from these sources,
including those which address diesel particulate matter (PM).
The Strategy by itself doesn't automatically result in regulation
or control of emissions. The EPA will perform further analyses of HAP
emissions, control methods, and health impacts, as appropriate, for
stationary and mobile sources. These analyses will inform any ultimate
regulatory requirements that EPA develops under the Strategy.
ADDRESSES: A docket containing information relating to the development
of this notice (Docket No. A-97-44) is available for public inspection
and copying between 8:00 a.m. and 5:30 p.m., Monday through Friday
except for Federal holidays, in the Air and Radiation Docket and
Information Center (MC-6102), Room M-1500, U.S. Environmental
Protection Agency, 401 M Street, SW, Washington, DC 20460; telephone
(202) 260-7548. The docket office may charge a reasonable fee for
copying.
FOR FURTHER INFORMATION CONTACT: Laura McKelvey, Office of Air Quality
Planning and Standards (MD-13), U.S. Environmental Protection Agency,
Research Triangle Park, North Carolina, 27711, telephone number (919)
541-5497, electronic mail address: McKelvey.Laura''epa.gov.
SUPPLEMENTARY INFORMATION:
Plain Language
In compliance with President Clinton's June 1, 1998 Executive
Memorandum on Plain Language in Government Writing, this package is
written using plain language. Thus, the use of ``we'' in this package
refers to EPA. The use of ``you'' refers to the reader and may include
State, local or Tribal government agencies, industry, environmental
groups, or other interested individuals.
Executive Order 12866
Under Executive Order 12866 (58 FR 51735, October 4,1993), the
Agency must determine whether a regulatory action is ``significant''
and therefore subject to Office of Management and Budget (OMB) review
and the requirements of the Executive Order. The Order defines
``significant'' regulatory action as one that is likely to lead to a
rule that may either: (1) have an annual effect on this economy of $100
million or more, or adversely and materially affect a sector of the
economy, productivity, competition, jobs, the environment, public
health or safety, or State, local or Tribal governments or communities;
(2) create a serious inconsistency or otherwise interfere with an
action taken or planned by another Agency; (3) materially alter the
budgetary impact of entitlement, grants, user fees, or loan programs or
the rights and obligations of recipients thereof; or (4) raise novel
legal or policy issues arising out of legal mandates, the President's
priorities, or the principles set forth in the Executive Order.
This notice was submitted to OMB for review. Any written comments
from OMB and written EPA responses are available in the docket.
Docket
The docket is an organized file containing information related to
the development of the Strategy. The main purpose of this docket is to
allow you to readily identify and locate documents relevant to the
development of the Strategy. The docket is available for public
inspection at the EPA's Air and Radiation Docket and Information
Center, which is listed in the ADDRESSES section of this document.
Electronic Access and Filing Addresses
You can get this notice and other background information in Docket
No. A-97-44 by contacting our Air and Radiation Docket and Information
Center (see ADDRESSES), or by visiting our website at ``http://
www.epa.gov/ttn/uatw/urban/urbanpg.html'' for electronic versions of
the notice and other information. For assistance in downloading files,
call the TTN HELP line at (919) 541-5384.
Outline
The information in this document is organized as follows:
I. National Efforts to Reduce Air Toxics
A. What is our overall air toxics program?
B. Why are we concerned about urban air in particular?
C. What is the Integrated Urban Air Toxics Strategy?
II. Federal Activities Related to the Integrated Urban Air Toxics
Strategy
A. What HAPs pose the greatest threat in urban areas?
B. How does EPA plan to address requirements for area sources of
HAPs?
C. What regulatory actions will EPA take to implement the
Strategy?
D. How do the various Federal authorities help EPA implement the
Strategy?
III. State, Local and Tribal Activities
A. Why are State, local and Tribal programs integral to the
process?
B. What are the objectives of State, local and Tribal
activities?
C. What were comments on the State/local/Tribal programs and how
are they being addressed in the Strategy development?
D. How can State, local or Tribal agencies participate in the
Strategy?
E. What elements should a State, local or Tribal program
contain?
IV. Assessment Activities
A. How will we assess progress toward goals?
B. What methods, tools, and data will we use to estimate risk?
C. What is our overall risk assessment approach for the
Strategy?
D. How will we design future assessments?
V. Knowledge and Tools
[[Page 38707]]
A. How will we review and expand ambient monitoring networks?
B. How will we update and maintain the emission inventory?
C. What air quality and exposure models will we use to implement
the Strategy?
D. What are the research needs and what is EPA doing to address
them?
VI. Public Participation and Communication
A. How will we encourage stakeholder involvement?
B. What is our overall timeline for action?
C. What reports will we prepare to communicate with the public?
Appendix A. Summary of other authorities, laws, rules, and programs
to help reduce HAP emissions
I. National Efforts to Reduce Air Toxics
The 1990 Clean Air Act Amendments provided the foundation for our
current air toxics program. This program is designed to characterize,
prioritize and equitably address the serious impacts of HAPs on the
public health and the environment through a strategic combination of
regulatory approaches, voluntary partnerships, ongoing research and
assessments, and education and outreach. Since 1990, we've made
considerable progress in reducing emissions of air toxics \1\ through
regulatory, voluntary and other programs. To date, our overall air
toxics program, summarized in section I.A., has focused on reducing
emissions of toxic air pollutants from major stationary sources through
the implementation of technology-based emissions standards as required
in section 112(d). These actions have resulted, or are projected to
result, in substantial reductions in HAP emissions.\2\ Additionally,
actions to address mobile and stationary sources under other Clean Air
Act programs are achieving reductions in HAP emissions (for example,
the phase-out of lead from gasoline). However, we expect that the
emission reductions that will result from these other actions are only
part of what will be necessary to protect public health and the
environment from toxic air pollutants. In identifying additional steps,
we'll use a risk-based focus to develop, implement and facilitate
additional Federal and local regulatory and voluntary measures.
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\1\ Our use of the terms ``air toxics'' or ``toxic air
pollutants'' in this notice refers specifically to those pollutants
which are listed under section 112(b) of the Act as ``hazardous air
pollutants'' or HAPs. There are currently 188 HAPs listed.
\2\ We project that by 2002, the full implementation of section
112(d) maximum achievable control technology (MACT) standards
adopted to date will yield emissions reductions of approximately one
million tons of HAPs per year. Within the next six years, completion
and full implementation of section 112(d) technology-based standards
for the remaining stationary source categories listed pursuant to
section 112(c) will contribute additional emissions reductions.
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In considering additional steps towards protecting human health and
the environment, we need to identify and focus on issues of highest
priority. Current information indicates that there are potentially
significant health risks associated with air toxics exposures affecting
large numbers of people in urban areas, as discussed in section I.B.
Recognizing this, Congress instructed us to develop a strategy for air
toxics in urban areas that includes specific actions to address the
large number of smaller, area sources,\3\ and that contains broader
risk reduction goals encompassing all stationary sources. More
specifically, section 112(k)(1) states:
\3\ Area sources are those stationary sources that emit, or have
the potential to emit, less than 10 tons per year of any one HAP or
less than 25 tons per year of a combination of HAPs. Examples
include hospital sterilizers and small publicly owned treatment
works.
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The Congress finds that emissions of hazardous air pollutants
from area sources may individually, or in the aggregate, present
significant risks to the public health in urban areas. Considering
the large number of persons exposed and the risks of carcinogenic
and other adverse health effects from hazardous air pollutants,
ambient concentrations characteristic of large urban areas should be
reduced to levels substantially below those currently experienced.
As the ambient concentrations of HAPs in urban areas result from a
combination of different sources (e.g., area, major,\4\ and mobile \5\)
emitting many of the same pollutants, we need to recognize
contributions from all types of sources in achieving the reductions in
ambient concentrations referred to in this subsection. Therefore, in
addition to addressing specific statutory requirements for area
sources, we've devised an integrated strategy for reducing cumulative
public health risks in urban areas posed by the aggregated exposures to
air toxics from all sources. The Integrated Urban Air Toxics Strategy
(the Strategy) presented here, and summarized in section I.C. below, is
one part of our overall national effort to reduce toxics. The basic
components of the Strategy consist of the same basic elements as those
of the overall air toxics program but with a specific focus on the
particular needs of urban areas.
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\4\ Major stationary sources are sources that emit, or have the
potential to emit, more than 10 tons per year of any one HAP or 25
tons per year of a combination of HAPs. Examples include chemical
plants, oil refineries, aerospace manufacturers and steel mills.
\5\ Mobile sources include motor vehicles (e.g., cars and
trucks) and off-road equipment (e.g., construction equipment and
lawn mowers), and their fuels.
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Before we describe the national efforts to control air toxics in
more detail, we want to provide a brief overview of what air toxics
are, their health and environmental effects, and their sources. These
topics are discussed in more detail later in the notice, but their
introduction here will help ensure that the remaining discussion in
section I is based on a common understanding of the nature of the air
toxics problem.
<bullet> What are air toxics?
The Act identifies 188 compounds as HAPs. They include pollutants
like benzene found in gasoline, perchloroethylene emitted from dry
cleaners, methylene chloride used as an industrial solvent, heavy
metals like mercury and lead, polychlorinated biphenyls (PCBs), dioxins
and some pesticides. These pollutants may cause cancer or other serious
effects in humans or in the environment. Health concerns result from
both short-and long-term exposures to these pollutants. They may
disperse locally, regionally, nationally, or globally and after
deposition may persist in the environment and/or bioaccumulate in the
food chain, depending on their characteristics (such as vapor
pressures, atmospheric transformation rates). Although not specifically
listed as a HAP in section 112(b) of the Act, diesel emissions contain
many HAPs, and are thus collectively considered under our overall
program and the Strategy.
<bullet> What health and environmental effects do they cause?
Hazardous air pollutants can cause many health effects. More than
half are known or suspected to be human carcinogens. Many are known to
have respiratory, neurological, immune or reproductive effects,
particularly for more susceptible or sensitive populations, such as
children. Many of the HAPs are known to also cause adverse effects in
many fish and animal species, including toxicity in fish or causing
reproductive decline in bird species, including endangered species.
These environmental effects may be felt by individual species within a
single level of the food chain or by the entire ecosystem where
multiple species are affected.
<bullet> What are the sources of air toxics?
There are literally millions of sources of air toxics, including
large industrial complexes like chemical plants, oil refineries and
steel mills; small (area) sources such as dry cleaners, gas stations,
and small manufacturers; and mobile sources including cars, trucks,
buses, and nonroad vehicles like ships and farm equipment.
[[Page 38708]]
A. What is Our Overall Air Toxics Program?
Our overall approach to reducing air toxics reflects the mandates
under the Act to develop technology-based standards and then
subsequently to implement a risk-based program to ensure the protection
of public health and the environment. For example, in amending the Act
in 1990, Congress required us to establish national standards to reduce
emissions of air toxics from stationary and mobile sources. Under
section 112(d), Congress emphasized the implementation of technology-
based standards for stationary source categories emitting air toxics.
These emission standards are known as maximum achievable control
technology (MACT) standards, and generally available control technology
(GACT) standards. Section 112(k) requires us to list area source
categories and to ensure 90 percent of the emissions from area sources
are subject to standards pursuant to section 112(d). In addition, under
section 202, Congress requires us to set standards to control HAPs from
motor vehicles and their fuels.
Further, the Act contains additional provisions that have a risk-
based focus. Section 112(f) of the Act requires us to evaluate the risk
remaining after implementation of MACT standards (i.e., the ``residual
risk'') in order to evaluate the need for additional stationary source
standards to protect public health and the environment.
Under section 112(k), the Act specifically mandated that we develop
a Strategy (the subject of this notice) to address public health risks
posed by air toxics from area sources in urban areas and report to
Congress on this issue. In addition, section 112(k) of the Act also
mandates that the Strategy achieve a 75-percent reduction in cancer
incidence attributable to HAPs emitted by stationary sources.
Other sections of the Act call for study of other types of specific
air toxics problems including a focus on certain HAPs that persist and
bioaccumulate in the environment. These studies include the deposition
of air toxics to Great Waters,\6\ HAP emissions from electric
utilities, and the health and environmental effects of mercury
emissions, in particular.\7\
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\6\ The Great Lakes, Chesapeake Bay, Lake Champlain and coastal
waters are collectively referred to as the ``Great Waters.''
\7\ These studies are required by sections 112(m), 112(n)(1)(A),
and 112(n)(1)(B), respectively.
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Our current national air toxics goal was developed to meet
requirements of the Government Performance and Results Act (GPRA),
which requires us to report on the status of our progress in
implementing our programs. That goal is to reduce air toxics emissions
by 75 percent from 1993 levels and to significantly reduce the risk to
the public of cancer and other serious adverse health effects caused by
airborne toxics. Because our knowledge and tools to assess the impacts
of these emissions on public health and the environment were limited
when we set this current goal, it reflects the straightforward intent
to reduce total air toxics emissions as a means to reduce risks
associated with exposure to air toxics. However, as we extend our
knowledge, develop better assessment tools and begin to address the
risks associated with these emissions as required by the Clean Air Act,
we intend to modify our goal to one directed specifically at risk
reductions associated with exposure to air toxics. In working toward
such a risk-based goal, we'll focus particularly on populations and
areas disproportionately impacted, including, for example, densely
populated areas, children at risk of developmental effects and people
who are highly exposed to water and food affected by air toxics (e.g.,
subsistence fishers living near contaminated water bodies). For more
information on assessments, see section IV for an explanation of the
assessment methods.
We intend to progress toward the program goal through a combination
of our authorities, regulatory activities and voluntary initiatives.
The overall approach to reducing air toxics consists of the following
four key components:
<bullet> Source-specific standards and sector-based standards. As
previously mentioned, section 112 specifies MACT/GACT standards, and
residual risk standards, as well as those area source standards which
are contemplated by the Integrated Urban Air Toxics Strategy.
Additionally, section 129 requires standards for solid waste
incineration and section 202(l) requires EPA, based on the mobile-
source related Air Toxics Study, to promulgate reasonable requirements
to control HAPs from motor vehicles and their fuels.
<bullet> National, regional, and community-based initiatives to
focus on multi-media and cumulative risks. Section 112(k)(4) requires
us to ``encourage and support area wide strategies developed by the
State or local air pollution control agencies.'' Our risk initiatives
will include State, local and Tribal program activities consistent with
the Integrated Urban Air Toxics Strategy on the local level as well as
Federal and regional activities associated with the multimedia aspects
of HAPs, such as the Great Waters program \8\ and initiatives
concerning mercury, and other persistent bioaccumulative toxics (PBTs).
Other Agency initiatives include collaboration between the air and
water programs on the impact of air deposition on water quality (e.g.,
by accounting for the contribution of air deposition to the total
maximum daily load (TMDL) of pollutants to a water body), and
collaboration between offices within EPA's air program to assess the
risks from exposures to air toxics indoors and to develop non-
regulatory, voluntary programs to address those risks.
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\8\ Under section 112(m) of the Act, we assess and report to
Congress on the deposition of air pollutants in the Great Lakes,
Chesapeake Bay, Lake Champlain, and coastal waters. The third report
to Congress on ``The Deposition of Air Pollutants to the Great
Waters'' will be released later this year.
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<bullet> National air toxics assessments (NATA). National air
toxics assessments will help us identify areas of concern, characterize
risks, and track our progress toward meeting our overall air toxics
program goals, as well as the risk-based goals of the various
activities and initiatives within the program, such as the Integrated
Urban Air Toxics Strategy. The NATA activities include expansion of air
toxics monitoring, improving and periodically updating emissions
inventories, national- and local-scale air quality, multi-media and
exposure modeling (including modeling which considers stationary and
mobile sources), continued research on health effects and exposures to
both ambient and indoor air, and use and improvement of exposure and
assessment tools. These activities will provide us with improved
characterizations of air toxics risk and risk reductions resulting from
emissions control standards and initiatives for both stationary and
mobile source programs.
<bullet> Education and outreach. In light of the scientific
complexity inherent in air toxics issues, we recognize that the success
of our overall air toxics program depends in part on our ability to
communicate effectively with the public about air toxics risks and
activities necessary to reduce those risks. This includes education and
outreach efforts on air toxics in the ambient as well as indoor
environments.
Following is a more detailed discussion of the activities under
each of the four components of the national program.
[[Page 38709]]
1. Source-specific Standards and Sector-based Standards
Maximum achievable control technology. The 1990 Clean Air Act
Amendments required us to use a ``technology-based'' and a performance-
based approach to significantly reduce emissions of air toxics from
major sources of air pollution. These reductions are to be followed by
a risk-based approach to address any remaining, or residual risks.
Under the ``technology-based'' approach we develop standards for
controlling the ``routine'' emissions of air toxics from each major
source within an industry group (or ``source category''). These
standards--known as ``maximum achievable control technology (MACT)
standards''--are based on emissions levels that are already being
achieved by the better controlled sources in an industry. This approach
assures citizens nationwide that each major source of HAPs will be
required to employ effective measures to limit its emissions.
Under this program, we listed for regulation 174 source categories
that emit the 188 HAPs listed under section 112(b). To date, we've
promulgated 43 standards regulating 78 source categories. We've
proposed an additional 7 standards covering 8 source categories. Five
source categories have been delisted. We're continuing to develop
standards to cover the remaining source categories.
Combustion standards. We've also issued final rules to control
emissions of certain air toxics from certain types of solid waste
combustion facilities. These rules, required under section 129 of the
Act, set emission limits for new solid waste combustion facilities and
provide emissions guidelines for existing solid waste combustion
facilities. These rules affect municipal waste combustors and hospital/
medical/infectious waste incinerators, which account for 30 percent of
the national mercury emissions to the air. By the time these rules are
fully implemented we expect them to reduce mercury emissions from these
sources by about 90 percent from current levels, and reduce dioxin/
furan emissions by more than 95 percent from current levels. We're
working on additional rules to address industrial and commercial waste
incinerators, other solid waste incinerators and small municipal waste
combustor units.
Residual risk. The residual risk program, required under section
112(f) of the Act, is designed to assess the risk from source
categories after MACT standards are implemented. If we find a
remaining, or residual, risk, we're required, within 8 years of the
promulgation of the MACT standard, to set additional standards if the
level of residual risk doesn't provide an ``ample margin of safety to
protect public health'' or ``to prevent, taking into consideration
costs, energy, safety, and other relevant factors, an adverse
environmental effect.'' \9\
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\9\ The Residual Risk Report to Congress, March 3, 1999,
describes our approach on risk assessment methods for use across the
air toxics program, and our approach for conducting residual risk
analyses. (EPA-453-/R-99-001)
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In analyzing residual risk, we'll conduct risk assessments
consistent with the Agency's human health and ecosystem risk assessment
technical guidance and policies. We'll use a tiered approach, usually
first conducting a screening level assessment for a source category,
and move to a refined assessment only where the risks identified in the
screening assessment appear unacceptable. Depending on the
characteristics of the HAPs, these assessments will address single or
multiple pathways of exposure as well as human and ecological
endpoints.
Risk management decisions will be consistent with Agency policies.
For carcinogens, we'll use a linear dose-response model unless data
support nonlinear mechanisms. We'll follow the Agency's mixtures
guidelines where a source category emits multiple HAPs.
For non-cancer effects, we'll use the EPA reference concentration
or comparable criteria from other government agencies. As with the
cancer effects, we'll follow the mixtures guidelines for emissions of
multiple non-carcinogens.
In general, we'll base decisions on exposures predicted from
modeling HAP emissions in air and, where appropriate, other media.
Where available, we'll include monitoring data as part of our analysis
for refined assessments. We'll estimate the size and characteristics of
the exposed population, and conduct uncertainty and variability
analysis where appropriate.
Currently we're conducting analyses on 13 of the earliest standards
that we promulgated. We're conducting these analyses on a source
category basis. Depending on the outcome of these analyses, we may find
it necessary to modify our residual risk approach.
Mobile source standards. We started enforcing the first federal
emission standards for passenger cars in 1968. Since then, acting under
specific mandates from the Congress and under general authority, we've
developed emission standards for all types of highway vehicles, their
fuels, and engines used in virtually all varieties of mobile or
portable nonroad equipment such as tractors, construction vehicles,
recreational and commercial vessels, and lawn and garden equipment.
We've also made the emission standards more stringent over time. New
highway vehicles using gasoline are now all equipped with advanced
catalysts and computer-controlled fuel systems. Diesel vehicles and
most nonroad engines have been substantially redesigned to meet our
emission standards as well. Diesel buses in urban areas are subject to
a special limit on their emissions of particulate matter. All gasoline
and highway diesel fuel used in the United States is subject to
emission-reducing standards for volatility and sulfur, respectively.
About one-quarter of the gasoline used in the United States is now
subject to our reformulated gasoline program, and has lower volatility,
reduced concentrations of benzene and other aromatics, and other
beneficial changes. In May of this year, we proposed stringent new
standards for all cars and light trucks, and the gasoline they use. At
the same time we issued an advanced notice of proposed rulemaking to
solicit information relating to control of diesel fuel quality. This
year, we're also reviewing our standards for heavy-duty highway
vehicles. In 2001, we'll do the same for heavy-duty nonroad engines.
To date, most of our emission standards have been aimed at
improving urban air quality for the criteria pollutants carbon
monoxide, ozone, and PM10. However, the emission control equipment on
engines and vehicles, along with the fuel changes that have been needed
to meet our emission standards, are also effective at reducing
emissions of many HAPs. Our requirement to reduce and then end the use
of lead additives in gasoline is an example of a standard that
specifically reduced emissions of toxic pollutants. The reformulated
gasoline program is another example, as it includes a performance
standard for the emissions of several important HAPs.
Because of the time it takes for older vehicles to retire and be
replaced with newer vehicles that comply with the latest emission
standards, total mobile source toxics emissions will decline for many
years into the future.
While the toxic reductions from our emission standards have been
large, prior to 1990 we had no specific directions from Congress for a
planned program to control toxic emissions from mobile sources.
However, section 202(l), added by the Clean Air Act Amendments of 1990,
requires us to complete a study of motor vehicle-related air toxics,
and to promulgate
[[Page 38710]]
requirements for the control of HAPs from motor vehicles based on that
study. We completed the required study in 1993, and are presently
preparing an update to that study, and considering rulemaking under
section 202(l)(2). In addition, the 1990 Amendments give us
discretionary authority to control toxic emissions from nonroad mobile
engines. We plan to study the role of nonroad engines in the air toxics
problem over the next couple of years, and may propose standards if
appropriate.
2. National, Regional, and Community-based Initiative to Focus on
Multi-media and Cumulative Risks
The Clean Air Act requires a number of risk studies to help us
better characterize risk to the public and the environment from HAPs.
Information from these studies will provide information for rulemaking
in some cases but will also provide information to support national and
local efforts to address risks through other voluntary and pollution
prevention programs. The following paragraphs describe these studies.
Utility study. Section 112(n)(1)(A) of the Act requires ``a study
of the hazards to public health reasonably anticipated to occur as a
result of emissions by electric utility steam generating units of
pollutants listed under subsection [112(b)].'' We completed this study
in February of 1998. We're currently collecting additional information
to support a determination on whether regulations are appropriate and
necessary to address risks from HAPs from these sources. We expect all
test reports required under our information requests by May 31, 2000.
We'll use this information to conduct additional analysis of the
emissions of mercury from utilities and potential control technologies.
In addition, we'll continue the analysis of health-related issues. We
plan to make our determination about the need for regulation by
December 15, 2000.
Great Waters Program. Section 112(m) requires us to monitor, assess
and report on the deposition of HAPs to the ``Great Waters,'' which
include the Chesapeake Bay, Lake Champlain, the Great Lakes, National
Estuary Programs, and National Estuarine Research Reserves. We're
required to assess deposition to these waters by: establishing a
deposition monitoring network; investigating the sources of pollution;
improving monitoring methods; evaluating adverse effects; and sampling
for the pollutants in aquatic plants and wildlife. Pollutants of
concern to the Great Waters include mercury, lead, cadmium, nitrogen
compounds, polycylic organic matter/polynuclear aromatic hydrocarbons
(POM/PAHs), dioxin and furans, PCBs and seven banned or restricted
pesticides.
We're also required to provide an update to Congress every two
years on any new information relating to deposition of HAPs to the
Great Waters. We issued the first two reports to Congress in 1994 and
1997. In addition, in March 1998, we made a determination under section
112(m)(6) that we have enough authority under the Act to address the
HAPs impacting the Great Waters. The third report to Congress is
scheduled for September 1999, and will focus on the contribution of
atmospheric deposition, environmental and public health effects,
sources of pollution, and exceedences of standards.
As part of the Great Waters Program, we're funding special
monitoring studies at 13 different coastal areas. In addition, we're
expanding the National Atmospheric Deposition Program to include more
coastal sites for long-term deposition records. We'll continue to
develop a coastal monitoring network and to improve air deposition
monitoring methods.
In an effort to coordinate programs under the Clean Air Act and the
Clean Water Act, we're conducting a pilot study to link air dispersion
and deposition models with watershed fate and transport models. The
results of this study will help us to improve our multimedia analysis
efforts and will allow us to look at the connection between our legal
authorities under the two Acts.
Mercury study. Section 112(n)(1)(B) requires that we issue a report
to Congress on the sources and impacts of mercury. We released the
report in December 1997. The report included an assessment of the
emissions of mercury from all known anthropogenic sources in the United
States, the health and environmental implications of these emissions,
and the availability and cost of control of these emissions.
Urban Air Toxics Strategy. Section 112(k) of the Act requires us to
develop a strategy to identify and address risks to the public in urban
areas. We'll describe the Integrated Urban Air Toxics Strategy in more
detail in later sections of this document.
3. National Air Toxics Assessments (NATA)
As mentioned previously, in order for the national air toxics
program to move to a more risk-based program, it's imperative that we
have strong analytical tools to support activities to identify risks,
to track progress toward risk goals and to help prioritize our efforts
to address emissions and risks from air toxics. Several assessment
activities are under way to support the national air toxics program, as
described in the following paragraphs.
Federal air toxics monitoring. Ambient air toxics information is a
key component in supporting assessment activities, helping to determine
exposure, tracking progress of the air toxics program goals, and
evaluating models and other assessment tools. Because of the importance
of this information, we're currently developing an approach to
monitoring air toxics nationally and locally with State and local
agencies. We envision a monitoring network with some monitors operated
on the national level to track overall national trends. This monitoring
network may include both new monitoring sites located for air toxics
monitoring, as well as information leveraged from other national
monitoring networks including Photochemical Assessment Monitoring
Stations (PAMS) (which collect at least eight HAPs) and the PM2.5 sites
(which collect most of the metals). We'll also compile data from the
State toxics monitoring networks.
In order to optimize our monitoring resources, we're working with
our regulatory partners to expand monitoring networks by adding new
sites; merging existing Federal and States sites where appropriate
(e.g., PACS, PM2.5 and Speciation Trends sites); targeting urban
population-oriented sites; developing a common Acore'' list of
compounds to monitor; and implementing a phased approach to expanding
the number of sites and compounds to fill the data gaps.
Emissions inventories. Over the past several years we've worked to
build a program for a national inventory of air toxics emissions. We
now have data sets for the 1990 to 1993 period and a draft for 1996.
The 1996 National Toxics Inventory (NTI) will be used as part of the
NATA for modeling and data analyses. It includes information generated
from MACT standards development, as well as information provided by 36
States and various industries. The 1996 NTI is currently under review
by the State and local agencies. We expect the 1996 NTI to be final in
the fall of 1999.
Modeling. The NATA will include modeling efforts using information
from the emissions inventory and supported by the monitoring data.
We're working toward a future focus on integrated multi-media/
multipathway assessments. We intend to conduct assessments on the
national, regional, and local scales
[[Page 38711]]
to support activities at all levels of the air toxics program.
Initially we'll use the Assessment System for Population Exposure
Nationwide (ASPEN) model (used in the Cumulative Exposure Project) to
conduct national level assessments.
In the fall and winter of 1999, we'll conduct national level
assessments to estimate ambient concentrations of HAP and predict the
exposures that would result. This information will be released in the
spring of 2000. These assessments are described in more detail in
section IV.D.
In addition, we intend to use air quality and exposure models for
source-specific assessments and to look at selected urban areas. In the
near future, we expect to use the Total Risk Integrated Model (TRIM) to
address local or neighborhood scale applications. This model will have
the capability to address human health and ecological impacts. We
expect this to be available late in 2000. In addition, we're working on
a Models-3/Community Multi-scale Air Quality (CMAQ) Modeling System.
Initially, this model will support assessments on the urban-to
regional-scale. Eventually, however, it will be used for neighborhood-
scale assessments. By the end of 2000, we expect to have an operational
evaluation of the model using mercury and some semi-volatile compounds,
with a final evaluation completed by 2001. This model includes
capabilities to address ozone and PM, together with air toxics, and
will be able to link with a human exposure model.
4. Education and Outreach
We believe that public participation is vitally important in the
implementation of the overall air toxics program. We're committed to
work with cities, communities, State, local and Tribal agencies, and
other groups and organizations that can help implement our approach to
reducing toxics emissions. For example, we expect to work with the
cities, our regulatory partners, and other interested stakeholders in
the national air toxics assessments that will be conducted. In
addition, we'll continue to work with stakeholders on regulation
development. We intend to involve local communities and industries in
development of local risk initiatives such as the total maximum daily
load (TMDL) initiatives.
B. Why Are We Concerned About Urban Air in Particular?
In urban areas, toxic air pollutants raise concerns because sources
of emissions and people are concentrated in the same geographic area,
leading to large numbers of people exposed to the emissions of many
HAPs from many sources. Additionally, while urban exposures to some
pollutants may be fairly similar across the country, studies in a
number of urban areas indicate that exposures to other pollutants, and
any associated risks, may vary significantly from one urban area to the
next. The tools we rely on in our efforts to better characterize urban
health risks from air toxics each have associated uncertainties, which
may add to our concerns. We intend our NATA activities to improve our
ability to describe these uncertainties and where possible, reduce
them. As currently available, the various types of information (e.g.,
emissions, ambient air quality monitoring and modeling) that will be
central to our NATA activities illustrate the importance of focusing on
urban areas.
First, our baseline national emissions inventory \10\ for the air
toxics program indicates that the vast majority of HAP emissions
(approximately 75 percent of the total HAP emissions of all 188 HAPs
from all sources) are within counties with urban areas.\11\
Additionally, a greater number of different HAPs may be emitted from
the multiple sources present in urban areas than from the more limited
number and variety of sources present in rural areas. This is
particularly important because even in cases where individual pollutant
levels are low enough that exposure to any one pollutant wouldn't be
expected to pose harm, some pollutants may work together such that
their potential for harm increases and exposure to the mixture poses
harm. Thus, depending on exposure levels and characteristics of the
pollutants, multiple pollutant exposures, which may be prevalent in
urban populations, may pose increased public health risks.
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\10\ The baseline national toxics inventory (NTI) that we've
compiled over the past few years is representative of the years
1990-93. We believe that this is an appropriate baseline because
these years represent the ``pre-MACT'' emissions for HAP sources.
This baseline inventory contains information on major, area and
mobile sources for all 188 HAPs and provides information on whether
the emissions are urban or rural. A subset of this baseline
inventory is information collected and extensively reviewed by the
public to support analyses for this Strategy and regulatory actions
under section 112(c)(6).
\11\ In estimating the amount of emissions from urban areas,
we've totaled emissions from all U.S. counties that include a
metropolitan statistical area with a population greater than 250,000
or for which more than 50 percent of the population has been
designated ``urban'' by the U.S. Census Bureau. For a more detailed
description of emissions allocation, see the emissions information
prepared to support this Strategy (``Emissions Inventory of 40
Candidate Section 112(k) Pollutants; Supporting Data for EPA's
112(k) Regulatory Strategy''), available at www.epa.gov/ttn/uatw/
112k/112kfac.html.
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Second, ambient air monitoring information collected by States in
certain metropolitan areas during the 1990s demonstrate the
simultaneous presence of many HAPs in urban air and, thus, the
potential for urban population exposures to multiple HAPs. In assessing
the implications of these monitored HAP concentrations for potential
public health concerns, we combined the measured ambient HAP
concentrations with quantitative estimates of each HAP's cancer
potency. This limited evaluation of a subset of the small number of
HAPs monitored indicates the presence of HAPs in some cities that when
evaluated cumulatively is suggestive of upper bound estimates of
additional cancer risks at or above one in ten thousand.\12\ This type
of limited evaluation can provide indications of potential public
health concerns, but should not be considered a characterization of
actual health risks.
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\12\ The technical support documentation for this assessment
analysis is available from the public docket and includes a
presentation of ambient monitoring data in 17 cities for a variety
of HAPs. Also presented are the upper bound estimates of excess
cancer associated with continuous lifetime exposures at those
concentrations.
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Third, an early effort by the Agency to model ambient HAP
concentrations on a national scale performed for EPA's Cumulative
Exposure Project (CEP) suggests that HAP exposures are prevalent
nationwide, and that for some HAPs, in some locations, concentrations
are significantly higher than the concentrations that, if exposures are
continuous over a lifetime, are associated with a one-in-one million
lifetime excess cancer risk.\13\' \14\ As stated above, estimated
concentrations greater than risk-based concentrations should be viewed
as indicators of a potential public health problem and not as
characterizations of actual health risks. Illustrating the need for
special attention in urban areas, the early modeling analysis found
that for 75 percent of the HAPs modeled, the average estimated
concentrations in urban census tracts \15\ were greater, and in some
cases much greater, than the overall national average concentrations.
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\13\ SAIC. 1998. Final Report, Modeling cumulative outdoor
concentrations of hazardous air pollutants.
\14\ Woodruff, et al. 1998. Public Health Implications of 1990
Air Toxics Concentrations across the United States. Environ. Health
Persp. 106(5):245-251.
\15\ Census tracts with residential population density greater
than 750 persons per square kilometer.
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The concentration of activities in urban areas leads to the
presence of multiple emission sources and
[[Page 38712]]
proportionately higher emissions of multiple HAPs. Many of these
emission sources are area or mobile sources, and their emissions are
more likely to be released at ground level, where people are more
likely to be exposed to them. Because approximately 80 percent of the
U.S. population lives in metropolitan areas,\16\ exposures resulting
from urban air toxics emissions may pose a significant risk to public
health. Additionally, the prevalence of minority and low income
communities in urban industrial and commercial areas, where ambient
concentrations of HAPs may be greater, increases the likelihood of
elevated HAP exposures among these subgroups. The potential for air
toxics in urban areas, either directly or indirectly, to contribute to
elevated health risks among these and other subgroups (especially
including children, the elderly and persons with existing illness or
other potential vulnerability) demonstrates the need to assess risk
distributions across urban populations in order to address
disproportionate impacts of air toxics hazards.\17\
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\16\ U.S. Department of Commerce, 1997, Population Profile of
the United States. Current population reports, special studies P23-
194. Economic and Statistics Administration, Bureau of the Census,
Washington, D.C.
\17\ The reader should note that all of these examples
illustrate that there are different ways of representing urban
areas. These are all individually valid, but the result is that
different definitions lead to different approximations of the
affected population. In the remainder of the Strategy, we'll explain
which definition we're using in each particular context.
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As described earlier in this notice, we have been and are
continuing to develop various Federal standards for stationary and
mobile sources as part of the air toxics program and under other Clean
Air Act authorities. These standards, as well as standards developed by
State and local authorities, are expected to improve air quality in
urban areas. As part of the air toxics program, we will be assessing
what additional actions, both at the national and local level, are
needed to further improve air quality in urban areas. This is a primary
focus of the Integrated Urban Air Toxics Strategy, described more fully
in the rest of this notice. We will include State and local
authorities, and in particular mayors, in planning activities to assess
local air quality and to address concerns.
C. What is the Integrated Urban Air Toxics Strategy?
The Strategy presented in this notice has been developed in
response to the requirements of sections 112(k) and 112(c)(3) of the
Act, and also reflects activities to control mobile source emissions
required under section 202(l). As stated previously, the Strategy
represents an integration of our authorities to identify and address
risks from both stationary and mobile sources. In this section of the
notice, we describe the goals and major components of the Strategy,
while later sections describe more fully those components.
Additionally, section 112(k) of the Act also requires us to report to
Congress, on two occasions, regarding actions taken under the Strategy
and current information regarding public health risks posed by HAP
emissions in urban areas. We're currently preparing the first of these
two reports to Congress, and its release is planned for later this
year.
1. Goals of the Strategy
Our goals for the Strategy reflect both statutory requirements
stated in section 112(k) and the goals of our overall air toxics
program. These goals consist of the following:
<bullet> Attain a 75-percent reduction in incidence of cancer
attributable to exposure to HAPs emitted by stationary sources. This is
relevant to all HAPs from both major and area stationary sources, in
all urban areas nationwide. Reductions can be the result of actions by
Federal, State, local and/or Tribal governments, achieved by any
regulations or voluntary actions.
<bullet> Attain a substantial reduction in public health risks
posed by HAP emissions from area sources. This includes health effects
other than cancer posed by all HAPs. Reductions can be the result of
actions by Federal, State, local and/or Tribal governments, achieved by
any regulations or voluntary actions.
<bullet> Address disproportionate impacts of air toxics hazards
across urban areas. This will necessarily involve consideration of both
stationary and mobile source emissions of all HAPs, as well as sources
of HAPs in indoor air. We intend to characterize exposure and risk
distributions both geographically and demographically. This will
include particular emphasis on highly exposed individuals (such as
those in geographic Ahot spots'') and specific population subgroups
(e.g., children, the elderly, and low-income communities).
The Act includes certain specific requirements for the Strategy.
First, we're required to identify at least 30 HAPs, ``which, as the
result of emissions from area sources, present the greatest threat to
public health in the largest number of urban areas'' (section
112(k)(3)(B)(i) of the Act). Second, we're required to assure that
sources accounting for 90 percent of the emissions of identified area
source HAPs are subject to standards (section 112(k)(3)(B)(ii) and
section 112(c)(3)). These steps will contribute to our progress toward
the Strategy's goals.
In meeting the Strategy's goals, we'll consider reductions in HAPs
resulting, not only from actions under our overall air toxics program
(e.g., MACT, residual risk standards, mobile source emission controls)
and measures resulting from programs to attain the national ambient air
quality standards for particulate matter and ozone (as well as our
other regulatory programs), but also from State, local and Tribal
measures. Further, we'll consider cumulative risks presented by
exposures to emissions of HAPs from sources in the aggregate. This is
consistent with the language of section 112(k)(1) of the Act, quoted
earlier. Further, consistent with the direction of section 112(k)(4) to
encourage and support area-wide strategies developed by State or local
air pollution control agencies, we'll work with State, local, and
Tribal air pollution control programs for additional progress toward
these goals.
Continuous advances in our knowledge and activities within the
broader air toxics program, both of which are expected to contribute
especially relevant information, will be integral to the implementation
of the Strategy. For example, certain air toxics, such as mercury, may
be deposited from the air into soil and/or water, taken up by organisms
into the food chain, and bioaccumulate so that concentrations increase
through each level of the food chain. The result is that humans and
wildlife can be exposed to these ``air'' toxics by eating contaminated
food, especially predatory fish from affected water bodies. We're
concerned about individuals in urban areas that eat more than the
average amount of fish from local sources, including urban subsistence
fishers. Under the Great Waters program, we monitor air toxics
deposition and evaluate potential adverse effects on public health and
the environment including those related to contaminated ecosystems and
fish. This information will assist us in assessing the potential for
certain HAPs to pose multipathway health risks to urban residents of
coastal areas (e.g., risks from both inhalation of HAPs and consumption
of fish contaminated by deposition of HAPs to waterways).
The indoor environments program is another Agency activity with
particular relevance to the Strategy because people in urban settings
spend as much as 80
[[Page 38713]]
to 90 percent of their time indoors.\18\ Additionally, outdoor air is
brought indoors through infiltration and mechanical ventilation and
there are also many sources of air toxics indoors. As part of this
Strategy, EPA will assess the current information on indoor emissions
and air concentrations of air toxics, and will use the data, to the
extent possible, to estimate exposures to air toxics in indoor
environments. As we continue to develop and enhance our knowledge of
exposures and risks from indoor air toxics through the indoor
environments program, we'll seek to include information on indoor
exposures in our characterization of risk associated with outdoor
sources and in the development of risk management options for air
toxics. We also intend to conduct additional research on indoor air
exposures to HAPs and on the relative significance of outdoor and
indoor concentrations of HAPs, as well as on the relationship between
outdoor emission sources and indoor concentrations of HAPs.
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\18\ The indoor environments program is a non-regulatory
program, working under the authority of Superfund Amendments and
Reauthorization Act (SARA) Title IV to perform research and provide
information to the public on the health problems associated with air
pollutants in the indoor environment. Most of the guidance provided
by the indoor environments program focuses on reducing pollutants
throughout buildings through proper building design, operation, and
maintenance, including management of indoor sources. The program
works through an extensive network of partners in providing training
and information on indoor air environmental issues throughout the
United States.
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2. Developing the Strategy
To address the problem of exposure to air toxics in urban areas, we
published a draft strategy on September 14, 1998 (63 FR 49240) that
addressed the urban air toxics risks from both stationary and mobile
sources. We asked for, and received, extensive public comment on the
draft strategy. We received over 120 letters and heard from numerous
speakers at stakeholder meetings in Alexandria, VA; Durham, NC;
Chicago, IL; and San Francisco, CA, as well as at other meetings
including a public meeting in New York City and meetings with the
National Environmental Justice Advisory Council. As discussed
throughout the following sections of this notice, we considered these
comments in developing the final Strategy. Comment letters, meeting
summaries, and material developed to analyze and respond to comments
are in the public docket (Docket No. A-97-44).
The Strategy being published today will produce a set of actions in
response to the cumulative public health risks presented by exposures
to emissions of multiple HAPs from multiple sources. We believe that by
considering urban air toxics emissions from all sources, we'll better
understand and address the relative risks posed by any one pollutant
and/or source category. Thus, by integrating activities under different
parts of the Act, we can more realistically address aggregate exposure
in areas where the emissions and risks are most significant and
controls are the most cost effective.
3. Components of the Strategy
Consistent with the broader overall air toxics program (described
in section I.A.), the Strategy is made up of four interrelated parts or
components for addressing the public health risk associated with urban
air toxics. Information from each of the four components provides
feedback to the others to inform the decisions needed to make progress
toward meeting our goals.
The first component includes our regulatory tools and programmatic
activities for source-specific and sector-based standard setting, as
well as those of States, local agencies, and Tribes, which contribute
to reductions in emissions of air toxics from major, area, and mobile
sources. This component includes activities such as selecting urban
HAPs, setting emission standards, conducting studies, developing
policies, and conducting enforcement and compliance assistance
activities. These actions result in emission reductions, as well as
associated reductions in risk. Sections II and III of this document
describe the regulatory activities we'll pursue to implement the
Strategy.
The second component of the Strategy involves local and community-
based initiatives to focus on multi-media and cumulative risks within
urban areas. These may include activities such as pilot projects to
identify and address risk, and may rely on some of the assessment
activities and tools described below. Section III of this document
describes the nature of some of these activities.
The third component is the urban component of NATA, which will
provide us with meaningful information and allow us to describe
progress that we've made in meeting our overall program and strategy-
specific goals. We'll identify the pollutants and sources that
contribute to any failures in meeting our risk reduction goals, and
provide meaningful information to support regulatory and policy
decisions needed to move us closer to meeting them. Section IV of this
document, Assessment Activities, describes how we'll design and conduct
these assessments. These activities rely on our improving base of
knowledge (e.g., concerning health effects and exposure
characteristics) and tools (e.g., emissions inventories, monitoring
networks, and computer models), which are described in section V, along
with our plans for their improvement and related research.
The fourth component, communicating about risk through education
and outreach to the public, ensures that the activities we undertake
are responsive to your concerns. We'll depend on stakeholder
involvement at the national and local levels to implement the Strategy.
Section VI explains how we'll communicate with the public on these
issues.
We've formulated an integrated Strategy to characterize,
prioritize, and equitably address the public health impacts of HAPs in
urban areas. The Strategy relies on a strategic combination of
regulatory approaches and voluntary partnerships, both of which are
based on ongoing research and assessments, and include educational
outreach. Sections II through VI of this document explain how the
components described above work, how they'll be expanded and improved,
and how we expect to meet our goals to reduce risk from HAPs.
4. Overview of the Strategy
The Integrated Urban Air Toxics Strategy, in conjunction with the
overall air toxics program, will continue to lower human exposure to
air toxics by reducing emissions. Progress will be achieved by:
<bullet> Completing MACT standards.
<bullet> Addressing residual risk.
<bullet> Implementing the urban air toxics strategy.
<bullet> Enhancing our ability to characterize risk and estimate
exposures.
<bullet> Developing new tools for monitoring progress with the
goals of the air toxics program.
<bullet> Developing a monitoring network.
<bullet> Effectively implementing and enforcing standards.
We'll achieve these objectives by following the guiding principles
of the air toxics program:
<bullet> Working cooperatively and effectively with State and local
communities.
<bullet> Focusing on communities, susceptible populations, and
sensitive ecosystems.
<bullet> Providing cost-effective, common-sense solutions to
problems, through flexible strategies.
<bullet> Developing and executing an effective education and
outreach program.
[[Page 38714]]
The Strategy will bring together the four basic components
(standards, initiatives, assessment, and outreach). It will be an
iterative and evolving process that will use existing programs and
tools to target risk reduction and to continually assess risk and
measure progress.
II. Federal Activities Related to the Integrated Urban Air Toxics
Strategy
A. What HAPs Pose the Greatest Threat in Urban Areas?
This section provides further discussion of what air toxics are,
the concerns they present, and describes how we evaluated and selected
a list of HAPs to guide our actions under the Strategy. In brief, we
evaluated the health effects information available for the 188 HAPs,
estimated emissions from all known sources using a variety of
techniques, assessed available air quality monitoring data, reviewed
existing studies, and produced a list of pollutants based on the
relative hazards they pose in urban areas, considering toxicity,
emissions, and related characteristics. From this effort, we
established a list of urban HAPs which pose the greatest threats to
public health in urban areas, considering emissions from major, area
and mobile sources. Among these urban HAPs are a subset of the 30 HAPs
having the greatest emissions contribution from area sources (the
``area source HAPs'').
1. Air Toxics Defined
Section 112(b) of the Act identifies 188 toxic chemicals as HAPs.
Hazardous air pollutants include a wide variety of organic and
inorganic substances released from industrial operations (both large
and small), fossil fuel combustion, gasoline and diesel-powered
vehicles, and many other sources. The major categories of toxic air
pollutants include volatile organic compounds (known as VOCs), metals
and inorganic chemicals, and semi-volatile organic chemicals. Volatile
chemicals are usually released into the air as vapor, while semi-
volatile organics and metals may be released in the form of particles.
Additionally, 17 of the 188 HAPs are defined as chemical groups rather
than unique chemicals. In evaluating the health effects, emissions and
monitoring information for these chemical groups we made specific
decisions regarding our treatment of the available information for the
group or the individual chemicals represented by the group (see the
technical support document in the public docket for the identification
of the urban HAPs).
Of the 17 chemical groups, polycyclic organic matter (POM) posed
particular complications. Polycyclic organic matter is defined in
section 112(b) of the Act as organic compounds with more than one
benzene ring and a boiling point greater than or equal to 100 deg.C,
which encompasses a complex mixture of thousands of polynuclear
aromatic hydrocarbons (PAH). Among the many PAH constituents of POM are
seven compounds (benzo[a]anthracene, benzo[a]pyrene,
benzo[b]fluoranthene, benzo[k]fluoranthene, chrysene,
dibenzo[a,h]anthracene, and indeno[1,2,3-c,d]pyrene) that we've
identified as probable human carcinogens. For the evaluation of POM as
a potential public health threat in urban areas, and for the subsequent
source category analysis, we used this group (referred to as 7-PAH) as
a surrogate for the much larger, more complex and diverse mixture of
POM.
The 188 HAPs have been associated with a wide variety of adverse
health effects, including cancer, neurological effects, reproductive
effects and developmental effects. Additionally, the specific health
effects associated with the various HAPs may differ, depending on the
particular circumstances of exposure (e.g., the amount of chemical, the
length of time a person is exposed, the stage in life of the person
exposed). We've classified many of the HAPs as ``known,'' ``probable,''
or ``possible'' human carcinogens and have included this information in
our Integrated Risk Information System.\19\ The HAPs can also be
described with regard to the part of the human body to which they pose
threats of harm. For example, neurotoxic pollutants cause harm to the
nervous system. Other effects include cardiovascular, and respiratory
effects, as well as effects on the immune system and reproductive
system. The severity of harm can range from headaches and nausea to
respiratory arrest and death. The level of severity differs both with
the amount and length of exposure and the chemical itself (e.g., how it
interacts with individual components of the nervous system). Some
chemicals pose particular hazards to people of a certain age or stage
in life or even based on their ethnic background. For example, some
HAPs are developmental toxicants. That is, exposure to certain amounts
of these chemicals during a woman's pregnancy or exposure of infants or
children can prevent normal development into a healthy adult. Other
HAPs are reproductive toxicants, meaning they may have the potential to
affect the ability of adults to conceive or give birth to a healthy
baby.
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\19\ The Integrated Risk Information System (IRIS), prepared and
maintained here at EPA, is an electronic data base containing
information on human health effects that may result from exposure to
various chemicals in the environment. IRIS was initially developed
in response to a growing demand for consistent information on
chemical substances for use in risk assessments, decision-making and
regulatory activities. The information in IRIS is intended for those
without extensive training in toxicology, but with some knowledge of
health sciences. Further information about IRIS, including the
information it contains, can be found on the IRIS website at http://
www.epa.gov/iris.
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In addition, we're currently investigating the health risks
associated with the mixture of compounds that comprise diesel exhaust
which originates primarily from mobile sources. While not specifically
listed as one of the 188 HAPs, diesel exhaust includes many HAPs,
including chemicals that fall into the group of POM chemicals, as well
as some HAP metals and volatile organic compounds. In addition, we're
concerned about the potential health risks from the particulate matter
component of diesel exhaust. Diesel particles are characteristically
small and fall within the size range of inhalable particles addressed
by the national ambient air quality standards for particulate
matter.\20\ Our draft health assessment of diesel emissions identifies
lung cancer as well as several other adverse respiratory health
effects, including respiratory tract irritation, immunological effects,
and changes in lung function, as possible concerns for long-term
exposures to diesel exhaust.\21\ If new diesel engine models are used
in an increasing share of the light duty fleet,\22\ concerns regarding
potential
[[Page 38715]]
health risks from diesel exhaust will become more significant.
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\20\ Inhalable particles are defined as particles of aerodynamic
diameter less than or equal to 10 micrometers.
\21\ Health Assessment Document for Diesel Emissions, SAB Review
Draft, U.S. Environmental Protection Agency, Washington, D.C. EPA/
600/8-90-057C, February 1998. The evidence comes from studies
involving occupational exposures and/or high exposure animal
studies. The Health Assessment, when completed, will recommend how
the data should be interpreted for lower environmental levels of
exposure. The draft Health Assessment is currently being revised to
address comments from a peer review panel of the Clean Air Science
Advisory Committee (CASAC Review of the Draft Diesel Health
Assessment Document, U.S. Environmental Protection Agency Science
Advisory Board, Washington, D.C. EPA-SAB-CASC-99-001. The CASAC will
review these revisions later this year.)
\22\ Diesel engines in highway and nonroad mobile sources are
numerous and widespread. Heavy-duty highway and nonroad diesel
engines are the largest sources of diesel exhaust emissions. While
diesel engines are used in a relatively small number of cars and
light-duty trucks today, vehicle and engine manufacturers are
developing new engine models that may be used in an increasing share
of the light-duty fleet, particularly light-duty trucks.
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As described above, HAPs and mixtures containing HAPs have the
potential to pose a variety of health risks depending on their chemical
characteristics, as well as the circumstances of human exposure. In the
following two sections, we describe our identification of HAPs of
particular concern in urban areas nationally.
2. The URBAN HAPs
Although information is limited regarding actual health risks posed
by specific HAP emissions, the availability of various other types of
information is sufficient to achieve our objective of identifying those
HAPs posing the greatest potential public health concern in the largest
number of urban areas. For the purpose of meeting the requirements of
section 112(k) and section 112(c)(3), we've listed in Table 1 the 33
HAPs that, on a national scale, we believe pose the greatest threat to
public health in the largest number of urban areas. Of these 33 HAPs,
29 appeared on the draft urban HAPs list published in our September 14,
1998 Federal Register document (63 FR 49240). Changes to the list
resulted from changes made to the method for urban HAPs selection, the
input data and the final selection criteria upon consideration of
comments received on the draft list and its supporting methodology.
\23\
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\23\ The final list includes beryllium compounds,
hexachlorobenzene, polychlorinated biphenyls and 1,1,2,2
tetrachloroethane, which hadn't appeared on the draft list, and
doesn't include bis(2-ethylhexyl)phthalate (DEHP), 1,4-
dichlorobenzene, methyl chloride and methylene diphenyl diisocyanate
(MDI), which were on the draft list.
Table 1.--List of Urban HAPs for the Integrated Urban Air Toxics
Strategy
[``Urban HAPs List'']
------------------------------------------------------------------------
HAP CAS No.+HAP
------------------------------------------------------------------------
acetaldehyde............................................ 75070
acrolein................................................ 107028
acrylonitrile........................................... 107131
arsenic compounds....................................... ..............
benzene................................................. 71432
beryllium compounds..................................... ..............
1,3-butadiene........................................... 106990
cadmium compounds....................................... ..............
carbon tetrachloride*................................... 56235
chloroform.............................................. 67663
chromium compounds...................................... ..............
coke oven emissions*.................................... 8007452
1,2-dibromoethane*...................................... 106934
1,2-dichloropropane (propylene dichloride).............. 78875
1,3-dichloropropene..................................... 542756
ethylene dichloride (1,2-dichloroethane)................ 107062
ethylene oxide.......................................... 75218
formaldehyde............................................ 50000
hexachlorobenzene....................................... 118741
hydrazine............................................... 302012
lead compounds.......................................... ..............
manganese compounds..................................... ..............
mercury compounds....................................... ..............
methylene chloride (dichloromethane).................... 75092
nickel compounds........................................ ..............
polychlorinated biphenyls (PCBs)........................ 1336363
polycyclic organic matter (POM)......................... ..............
quinoline............................................... 91225
2,3,7,8-tetrachlorodibenzo-p-dioxin (and congeners and 1746016
TCDF congeners)........................................
1,1,2,2-tetrachloroethane............................... 79345
tetrachloroethylene (perchloroethylene)................. 127184
trichloroethylene....................................... 79016
vinyl chloride.......................................... 75014
------------------------------------------------------------------------
+ Chemical Abstracts System number.
* HAPs with less significant emissions contributions from area sources.
This list of 33 urban HAPs includes not only those with emissions
from area sources, but reflects the integrated nature of the Strategy
by including those posing public health concerns in urban areas
regardless of emissions source type. Included among the 33 urban HAPs
are the 30 HAPs with greatest emissions contributions from area sources
(i.e., the area source HAPs'').
In response to publication of our draft list of urban HAPs, we
received comments regarding our inclusion of HAPs emitted predominantly
from non-area sources. Several commenters said that it was
inappropriate to include HAPs for which area source contribution was
low or negligible. Although section 112(k)(3)(B)(i) only requires that
we list HAPs emitted from area sources, we believe that the public is
exposed to complex mixtures of pollutants, and that these pollutants
are emitted by all types of sources. In other words, the risk from
exposure to HAPs has public health implications regardless of the
source or source type from which they are emitted. Therefore, in the
interests of best protecting public health in urban areas, we've listed
the 33 HAPs in Table 1 considering the aggregate exposure potential of
mobile,
[[Page 38716]]
area, and major stationary source emissions combined. At the same time,
as described below, we've also identified the 30 HAPs with the greatest
area source contribution. Under section 112(k), there aren't any
specific regulatory implications of listing the other three HAPs.
However, we'll use all 33 HAPs in prioritizing efforts to address risk.
Section 112(k)(3)(B) of the Act requires us to identify not less
than 30 HAPs that are estimated to pose the greatest threat to public
health in the largest number of urban areas ``as the result of
emissions from area sources.'' The Act, however, doesn't state that
such threats must be exclusively the result of emissions from area
sources. Therefore, from the list of 33 urban HAPs (i.e., the HAPs that
pose the greatest threat to public health in urban areas because they
ranked highest relative to the other HAPs in the analysis discussed
above), we identified those 30 HAPs with the greatest contributions of
national urban emissions from area sources, thus ensuring consistency
with the specification in section 112(k)(3)(B)(i). Without these
contributions from area sources, the threat from these HAPs would not
be as great. Emissions of only the 30 area source HAPs were considered
in the area source category listing required under section 112(c)(3)
and section 112(k) and described in section II.B. of this document. The
other three HAPs in Table 1 for which area sources are less significant
contributors to total emissions (i.e., those HAPs noted on Table 1 with
an asterisk), can be addressed, as appropriate, using our other
existing authorities, as described in section II.C. of this document.
During the public comment period on the draft Strategy, we received
substantial comment regarding the role of diesel engine emissions among
urban air pollutants, with several commenters suggesting that we
include diesel exhaust among the priority urban HAPs. As described
earlier, diesel exhaust, although not specifically listed among the 188
HAPs in section 112(b) of the Act, is a particular type of emission
which is composed of many HAPs. We agree with commenters that diesel
exhaust plays an important role among urban air pollutants, and, as
previously mentioned, we're investigating the health risks associated
with diesel exhaust. Meanwhile, we plan to address diesel exhaust in
our section 202(l) rulemaking for air toxics from motor vehicles and
their fuels.
It's important to note that the list in Table 1 was generated based
on our best estimates representing 1990 national baseline air toxics
emissions and ambient concentrations for urban areas. For example,
implementation of technology-based standards for coke ovens has reduced
the benzene, coke oven gases, and POM from these sources by 80 percent
(or 1,408 tons per year) since 1993. In addition, certain urban areas
have reduced other benzene emissions by as much as 30 or 40 percent.
Much of this reduction is attributable to the implementation of mobile
source reformulated gasoline requirements. To insure that we
appropriately target reductions of urban air toxics to support the
protection of public health, it will be important to reevaluate our
priorities as we develop emissions estimates and obtain more
comprehensive monitoring information for more recent years.
3. Method to Identify the Urban HAPs.
This section summarizes how we identified HAPs for the urban HAPs
list. Our identification methodology included three separate analyses.
The results of these analyses were compared using specific criteria in
order to identify the urban HAPs. The three analyses relied on a
variety of information types including toxicity information, emissions
estimates, ambient monitoring, and air quality modeling. The
methodology is summarized here and more fully described in the
technical support document (``Ranking and Selection of Hazardous Air
Pollutants''), which is available through the public docket and on our
website.
In 1997, we conducted an initial screening evaluation using a
preliminary methodology. In addition to identifying HAPs for which we
separately conducted a public review of our national emissions
inventory information, this evaluation provided us with the opportunity
for peer review of our preliminary methodology. Like the methodology
relied on for our final list, this preliminary methodology relied on
various types of information relevant to potential health risks posed
by the 188 HAPs, and it integrated the results of three relative
rankings using the different types of information. This initial
screening run provided a starting point for focusing improvements in
the national emissions inventory and for evaluating and refining our
methodology for selecting the list of urban HAPs.
The preliminary methodology and screening analysis were reviewed by
a panel of outside experts. In early January of 1998, the preliminary
methodology was presented to the peer review panel in a written report.
A full day session of the peer review panel was held on January 21,
1998 to discuss the methodology and underlying data. The reviewers
evaluated all facets of the methodology and its suitability for
identifying HAPs for the urban HAPs list, the relative value of various
data sources, the availability of additional data sources, the
scientific validity of assumptions, consistency across the methodology
and appropriate presentation formats. Reviewers provided oral comments
at the January 21 meeting, as well as written comments before and after
the meeting. The final methodology described here has incorporated
revisions made to address comments raised by the January 1998 peer
review.
Comments were also received from the public in response to our
publication of the draft list of urban HAPs (September 14, 1998, 63 FR
49240). Consideration of issues raised by some commenters led us to
modify certain aspects of both the identification methodology and the
underlying data inputs. These changes were not inconsistent with
recommendations made by the 1998 peer review panel. Consistent with
peer reviewer recommendations to use the available information in the
most robust manner, our final identification methodology integrates the
results of three separate analyses. These ranking analyses are
discussed in the following sections. Because each analysis focused on
different aspects of the available information, such that no one
analysis fully captured all important aspects of the urban air toxics
information, we and the peer reviewers agreed that all three of the
analyses should be performed and their results integrated, to yield a
more comprehensive methodology.
a. Analysis 1: Risk-related ranking indices. In the first of the
three analyses, we ranked HAPs by combining surrogates for toxicity
with surrogates for exposure into ranking indices. The surrogates for
toxicity were risk-based concentrations (RBCs) for inhalation or risk-
based doses (RBDs) for ingestion. The RBCs and RBDs were derived from
acute and chronic (cancer and non-cancer) health-based reference
values.\24\
---------------------------------------------------------------------------
\24\ Acute RBCs were set equal to risk management exposure
guideline levels (e.g., Acute Exposure Guideline Levels (62 FR
58839-51) or Emergency Response Planning Guidelines (American
Industrial Hygiene Association, 1998. Emergency response planning
guidelines and workplace environmental exposure guidelines.) for
mild, transient or no effects from short exposure periods, when
available. Additionally, two chronic RBCs and two chronic RBDs were
derived for each HAP for which the requisite data were available.
For carcinogenic HAPs, we compared the continuous exposure levels
associated with predicted upper-bound lifetime increased cancer
risks of one-in-one million and one-in-ten thousand to the
continuous exposure level (e.g., EPA's reference concentration)
estimated to be without adverse non-cancer effects in human
populations, including sensitive subgroups. We then set the two
chronic RBC or RBD values to the lower two of those three levels.
For other HAPs, both of the two chronic RBC or RBD values were set
to the continuous exposure level estimated to be without adverse
non-cancer effects in human populations, including sensitive
subgroups. A fuller discussion of these steps is included in the
technical support document.
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[[Page 38717]]
Types of information used as surrogates for exposure included
measured ambient concentrations and yearly emission estimates from
area, major and mobile sources in all urban areas nationwide. To
address the potential for certain HAPs to pose significant risks of
exposure through pathways other than inhalation (primarily by consuming
food with accumulated HAPs), one set of indices also incorporated
measures of bioaccumulation potential. As described in more detail in
the technical support document, a total of seven separate indices \25\
were calculated using these different types of toxicity and exposure
information. Lack of the requisite data prevented all seven indices
from being calculated for all of the 188 HAPs. The indices were
combined into a single HAP ranking.
---------------------------------------------------------------------------
\25\ Four of the indices relied on chronic RBCs and emissions or
monitoring information, two other indices relied on chronic RBDs
plus emissions and bioaccumulation information, and the seventh
index relied on acute RBCs and monitoring information.
---------------------------------------------------------------------------
During the public comment period, we received comments stating that
the role of monitoring information in the methodology should be
strengthened. Because ambient concentrations directly influence
people's exposure to HAPs and there are differences among HAPs in the
many variables affecting their behavior after being emitted into the
air, we agree that it is important that the monitoring information play
a strong role in this analysis. Relying solely on emissions information
in selection of the urban HAPs would ignore the many factors which
influence ambient HAP concentrations. Since the publication of the
draft list, we've expanded our monitoring database to increase both the
number of pollutants for which we have monitoring information and the
number of measurement values. We've also improved our treatment of non-
detect measurements, first by assuming undetected HAPs are present at
one half the detection limit (instead of omitting the observation), and
by omitting data altogether for HAPs having fewer than ten percent of
observations above the detection limit. These changes have improved the
technical basis of the ambient indices.
We also received comment stating that inappropriate weight was
assigned to those HAPs for which the acute index was developed. In the
analysis for the draft Strategy, the requisite information for
calculating this index (both an acute RBC and an estimate of short-term
peak exposure) were available for only 21 of the 188 HAPs. We
appreciate the issue raised by the commenter that, because of the
relatively small number of HAPs for which this index could be
calculated, it was not necessarily assigning HAPs the appropriate
emphasis. Through our improvements to the ambient database described
above, and by increasing the number of acute RBCs, we have addressed
this issue and reduced bias in this index.
Commenters also recommended increased emphasis on persistent,
bioaccumulative and multipathway pollutants for which non-inhalation
exposure pathways may be important. It's important to recognize that
persistent bioaccumulative toxics (PBTs) are also often multipathway
pollutants, because the pattern of exposure is frequently other than
inhalation. However, not all multipathway pollutants are PBTs.
One commenter said ``EPA should consider multi-pathway exposures
under 112(k) when there is sufficient evidence demonstrating that
airborne emissions of the listed HAP have both direct and indirect
exposure pathways, which have been clearly identified.'' Another said,
``It is appropriate to include compounds with exposure pathways other
than inhalation because these pathways are a true concern in urban
areas where atmospheric deposition of particulate phase HAPs is
occurring (i.e., lead, mercury, cadmium, dioxin and PCBs) and being
taken up by fish, garden vegetables or hand-to mouth activity observed
in infants.'' With regard to the PBTs, some commenters said PBTs should
have been given more thorough consideration for listing. They said the
risks from PBT exposure are high, and the concentrations of many PBTs
are higher in the urban than non-urban areas. We support the use of the
multipathway analysis to assess total human exposure, particularly in
the case of PBTs.
Additionally, commenters said that indices should be calculated so
that the size of index value differences among HAPs could be more
clearly observed, and any bias related to different numbers of HAPs
ranked by each index removed. Because we believe that both of these
issues are important, we changed the index calculation methodology to
address these recommendations. This change had its greatest impact on
the food chain pathway index, in which HAPs with high bioaccumulation
potential and ingestion toxicity received much higher index values.
Primarily as a result of this change, Table 1 now includes two
additional persistent, bioaccumulative HAPs--PCBs and
hexachlorobenzene--that were absent from the September 1998 draft list.
Hexachlorobenzene and PCBs, as well as mercury, cadmium, lead, POM and
dioxin (also identified as urban HAPs in Table 1), are among the
pollutants of concern for our Great Waters program. Additionally, PCBs,
mercury and dioxin were identified as pollutants of concern in the
Great Lakes by the International Joint Commission of the United States
and Canada. Hexachlorobenzene, PCBs, dioxins, mercury, and alkyl-lead
were targeted for virtual elimination in the Great Lakes in the 1997
Canada-United States ``Strategy for the Virtual Elimination of
Persistent Toxic Substances in the Great Lakes'', known as the
``Binational Toxics Strategy''.
Some commenters said that the identification methodology emphasized
cancer as a health effect and didn't consider other health effects
including asthma, birth defects and reproductive effects. The
methodology does, however, consider health effects other than cancer.
Reference values (RBCs and RBDs) for each HAP used in the analysis were
developed for the health effects believed to occur at the lowest
exposure. In the case of HAPs which, in addition to these other health
effects, also pose cancer risks, we developed RBC/RBD values for one-
in-one million and one-in-ten thousand predicted lifetime cancer risk
levels. These risk levels have historically been used to inform
environmental regulatory action. The cancer risk-based values were
compared to RBC/RBD values for the most sensitive non-cancer health
effect, and the lowest two RBC/RBD values for each HAP were used in the
calculation of the chronic indices. This step, and the inclusion among
the seven indices of an acute toxicity index based entirely on effects
other than cancer, was intended specifically to recognize the
importance of health effects other than cancer for some HAPs. Thus, we
believe that the assessment methodology provides a balanced
consideration of all health effects associated with each HAP, with
index calculation and the resultant ranking depending significantly on
effects other than cancer.
We also received comments regarding the toxicity information used
in the analysis. More specifically, commenters
[[Page 38718]]
suggested that in the case of 1,3-butadiene and vinyl chloride, we
should rely on draft assessments in progress rather than on assessments
currently available on IRIS. In the case of 1,3-butadiene, we agree
that the IRIS risk estimate is not an appropriate basis from which to
extrapolate human risk and the updated assessment has progressed to the
point where it is appropriate for use here.\26\ Use of this new
assessment, however, does not affect the presence of 1,3-butadiene on
the urban HAPs list. In the case of vinyl chloride, we've chosen to use
the Agency consensus assessment currently in IRIS rather than a draft
assessment that may yet change significantly. However, we've confirmed
that using the draft assessment for vinyl chloride wouldn't change its
status on the final urban HAPs list.
---------------------------------------------------------------------------
\26\ See April 27, 1999 internal memo, available in the public
docket.
---------------------------------------------------------------------------
Some commenters questioned the use of cancer-based RBC or RBD
values for certain HAPs to which the Agency has assigned a ``C'' weight
of evidence for carcinogenicity (``possible human carcinogens''). We
evaluated the supporting data for each ``C'' carcinogen that had been
proposed for listing to verify the appropriateness of the assessments
for use in this analysis. Many of these substances are currently the
subjects of research studies and EPA reassessment activities. In the
case of 1,4-dichlorobenzene, the currently available information led us
to modify our analysis so that the RBC and RBD values were based on
effects other than cancer. For all other ``C'' carcinogens, we retained
the RBC and RBD values. As updated information and assessments become
available for these and other HAPs, we intend to use that information
in analyses supporting future regulatory actions under the Strategy.
Other commenters questioned our assumptions as to the predominant
species of chromium and nickel in emissions and monitoring data.
Because the national monitoring and emissions data used in this
analysis don't differentiate among species of metals, we had to make
certain assumptions. To address the likelihood, supported by limited
available data, that all nickel present in emissions or ambient air
isn't in the form that is thought to have carcinogenic potential (e.g.,
nickel subsulfide and other insoluble forms), we applied the cancer-
based RBC for nickel subsulfide to 25 percent of the total emissions
and the ambient measurements for total nickel. We based this decision
on the assumption that no more than 50 percent of ambient nickel is
present in the insoluble form and no more than 50 percent of that is
present in the crystalline form. In the case of the ingestion pathway,
the non-cancer-based RBD was used. Regarding chromium, the limited
emissions and monitoring information available for both hexavalent and
total chromium indicated that approximately two thirds of the chromium
present in ambient air or national emissions is likely to be other than
the hexavalent form. Thus, we applied the cancer-based RBC for
hexavalent chromium to 35 percent of the total emissions and to 35
percent of the ambient measurement.
A few commenters requested an analysis of uncertainties surrounding
the calculations. To the extent that it's possible to conduct an
uncertainty analysis, we believe the process already includes one. The
calculation and presentation of seven different ranking indices,
instituted in response to comments from the January 1998 peer review
panel, is presented in graphic form in the technical support document.
These graphs show the range of ranking indices for each HAP, which we
regard as a measure of some of the uncertainty associated with this
identification methodology.
b. Analysis 2: Review of existing risk assessments and hazard
rankings. For the second analysis, we reviewed a number of air toxics
risk assessments or hazard rankings conducted previously by EPA staff,
State agencies or others.\27\ We selected 14 of the available studies
for use in this analysis, because they were sufficiently broad in the
pollutants evaluated, they included area sources of HAPs, and they
focused on the risks presented in urban areas. Each study provided a
risk-based ranking of HAPs, with separate rankings for cancer and, when
available, other health effects. The rankings within each study were
converted to a scale common to all of the studies, and the values were
summed across the studies, providing a total score for each HAP.
Because section 112(k) places special emphasis on area sources of HAPs,
scores were developed both for studies that considered combined
emissions from major, area, and mobile sources, and for studies that
considered emissions from area sources alone. From this analysis, we
identified those HAPs that, when compared across studies, consistently
ranked high.
---------------------------------------------------------------------------
\27\ These assessments and rankings, and the details of this
analysis, are described in the technical support document for the
identification of the urban HAPs, which is available in the public
docket.
---------------------------------------------------------------------------
c. Analysis 3: Cumulative Exposure Project (CEP). In the third
analysis, we used information provided by the CEP.\28\ In the CEP, the
Assessment System for Population Exposure Nationwide (ASPEN) model was
used with preliminary estimates of 1990 HAP emissions from all source
types to predict long-term average concentrations at the census tract
level for 148 HAPs. For some pollutants, modeled concentrations were
augmented with estimates of background levels that were intended to
represent contributions from natural sources, as well as historic
emissions of persistent pollutants. The estimated ambient
concentrations were then compared to risk-based concentrations (termed
benchmarks by the authors) intended to represent either continuous
exposure levels associated with a one-in-a-million upper bound estimate
of excess lifetime cancer risk, or continuous lifetime exposure levels
associated with no significant risks of adverse non-cancer effects
(e.g., EPA's Inhalation Reference Concentration (RfC)). As stated
earlier, estimated concentrations greater than risk-based
concentrations should be viewed as indicators of a potential health
problem, and not as a characterization of health risks. While we
recognize certain limitations associated with this initial attempt at
modeling HAP concentrations nationwide, and its inappropriateness for
use in drawing conclusions at small geographic scales, this modeling
effort is useful as a national screening tool. In this analysis, we
used the information generated by the CEP for urban areas and
identified those HAPs for which the modeled concentrations exceeded
risk-based concentrations in the greatest number of urban census
tracts.
---------------------------------------------------------------------------
\28\ See footnotes 13 and 14.
---------------------------------------------------------------------------
We received comments on several aspects of our use of the CEP
analysis in our method for identifying the draft urban HAPs list. Some
commenters felt that the addition of background concentrations was
inappropriate. Additionally, some commenters questioned the
appropriateness of the reference values used for some HAPs. We
recognized that the background value for one of the HAPs (bis(2-
ethylhexyl)phthalate or DEHP) was wrong, and we agreed that we should
focus the analysis on modeled concentrations resulting from
controllable sources. Additionally, we're currently using updated risk-
based concentrations which, in some cases, differ from those used in
the CEP analysis. Consequently, prior to using this analysis as part of
our final methodology, we repeated the analysis
[[Page 38719]]
for the subset of affected HAPs using the modeled concentrations
resulting only from current area, major and mobile sources (i.e.,
without addition of a background value) and an updated set of risk-
based concentrations. We've described the details of this reanalysis in
the technical support document in the public docket.
d. Integration of the three analyses. In selecting the urban HAPs
for the integrated Strategy, we compared the results of these three
separate ranking analyses and applied the following criteria when
integrating their results. We selected those HAPs for which a publicly
reviewed baseline national emissions inventory was available \29\ and
which had been either:
---------------------------------------------------------------------------
\29\ On June 20, 1997 we published notice of a draft listing of
source categories for regulation under section 112(c)(6) of the Act
(62 FR 33625). As part of this notice, we requested public review
and comment on the baseline national emissions inventory for the
seven pollutants identified under section 112(c)(6). In the fall of
1998, we requested and obtained public review on our baseline
national emissions inventory for 40 HAPs, five of which had also
been reviewed as part of the rulemaking process under section
112(c)(6). During both of these public reviews, many comments were
received on various aspects of the emissions information, and we
considered these comments in making improvements to the baseline
national emissions inventory for those HAPs. Details concerning
these two public reviews and documentation of the resultant
inventory information are presented in two documents (``1990
Emissions Inventory of Section 112(c)(6) Pollutants: Final Report''
and ``1990 Emissions Inventory of 40 Candidate Section 112(k)
Pollutants'') available at www.epa.gov/ttn/uatw/112c6/112c6fac.html
and www.epa.gov/ttn/uatw/112k/112kfac.html, respectively. The public
reviews provided us with an inventory that was appropriate for our
use on a national scale, in the identification of the urban and area
source HAPs. However, this baseline inventory may require certain
modifications for small scale detailed analyses such as those
described in section II.B.
---------------------------------------------------------------------------
<bullet> Identified by at least two of the three analyses
(regardless of area source contribution); or
<bullet> Identified by at least one of the three analyses and
having an area source contribution to total emissions of at least 25
percent.
The second criterion was set in recognition of the area source
emphasis of this integrated Strategy. These criteria produced an
integrated list of 33 urban HAPs.
As discussed earlier, section 112(k)(3)(B) of the Act requires us
to identify not less than 30 HAPs that are estimated to pose the
greatest threat to public health in the largest number of urban areas
as the result of emissions from area sources (``the area source
HAPs''). To identify these 30 area source HAPs, we ranked the list of
33 urban HAPs by percent contribution to national urban emissions from
area sources and selected the 30 urban HAPs with the greatest area
source contributions. The remaining three urban HAPs (i.e., coke oven
emissions, 1,2-dibromoethane, and carbon tetrachloride) have less
significant emissions contributions from area sources and aren't among
the 30 area source HAPs considered in the area source category listing
described in section II.C.
Some commenters on the draft Strategy were concerned that the
percent contribution to national urban emissions from area sources was
too low for some of the HAPs on the draft area source HAPs list, thus
not placing enough emphasis on risks from area sources. While we note
that the percent contribution from area sources for the area source
HAPs ranges down to as low as 2.9 percent, these values apply to total
urban emissions nationally. In individual urban areas as well as in
local communities within large areas, area sources may play a much
larger role. Because the Act requires us to select not less than 30
area source HAPs and because the percentage of emissions from area
sources will vary, we consider this an appropriate approach to identify
the area source HAPs on which the Strategy will focus in reducing area
source emissions and any associated health risks in individual urban
areas nationwide.\30\ Accordingly, this list of 30 area source HAPs was
used in identifying the list of new area source categories for which
standards will be addressed as required by section 112(c)(3) and
section 112(k)(3)(B)(ii).
---------------------------------------------------------------------------
\30\ Given the uncertainties and limitations associated with the
information upon which the 30 area source HAPs selection was based,
we don't believe that identifying greater than the statutory minimum
of 30 HAPs is warranted at this time.
---------------------------------------------------------------------------
B. How does EPA Plan to Address Requirements for Area Sources of HAPs?
1. Area Source Category Selection Approach in Draft Strategy
The Clean Air Act includes two provisions--sections 112(c)(3) and
112(k)(3)(B)(ii)--that instruct us to identify and list source
categories that contribute to the emissions of the 30 ``listed'' (or
area source) HAPs, and that are, or will be, subject to standards under
section 112 of the Act. The language in these two sections differs
slightly. Section 112(c)(3) requires us to list, pursuant to section
112(k)(3)(B), sufficient categories of sources ``to ensure that area
sources representing 90 percent of the area source emissions of the 30
[listed] hazardous air pollutants'' are subject to regulation under
section 112. As explained in the draft Strategy, this would seem to
allow us to regulate sources accounting for either 90 percent of the
combined emissions of all of the 30 area source HAPs, or 90 percent of
the emissions of each of the 30 area source HAPs. By contrast, section
112(k)(3)(B)(ii) requires us to identify sufficient categories to
``assure that sources accounting for 90 per centum or more of the
aggregate emissions of each of the 30 identified hazardous air
pollutants'' are subject to standards under section 112(d). This
language explicitly requires us to regulate sources accounting for 90
percent of the emissions of each of the 30 area source HAPs. As a
result, in the draft Strategy we adopted the interpretation that
allowed us to read the two provisions consistently, and assembled a
draft list of area source categories representing 90 percent of the
emissions of each of the 30 area source HAPs.
We adopted a two-step process for selecting the source categories
for the draft list. First we listed all of the area source categories
already subject to area source standards. For each of these source
categories we identified their percentage contribution to the total
area source emissions for each of the 30 area source HAPs. We then
listed additional area source categories as necessary, listing the
largest contributors first, until the list of area sources represented
90 percent of the emissions for each of the 30 area source HAPs.
2. Improvements in Area Source Category Information
Since issuing the draft Strategy, we've significantly improved our
emissions inventory data for many area source categories. (The final
information on the subset of pollutants of the baseline inventory used
in this analysis and a description of the changes made is in the
technical support document ``Emissions Inventory of 40 Candidate
Section 112(k) Pollutants; Supporting Data for EPA's Section 112(k)
Regulatory Strategy'' available at www.epa.gov/ttn/uatw/112k.) The
draft inventory for the subset of the HAPs of the baseline emission
inventory was available twice for public review. From this extensive
review, we received over 200 comments on the inventory, which were
addressed where data were provided. Based on the large number of public
comments, and information from internal comments, we've made many
changes to the baseline emissions inventory used to identify HAP
sources. In particular, better emission information for many of the
sources subject to section 112(d) MACT standards made a significant
difference in the inventory. The percent
[[Page 38720]]
contribution from major versus area sources for each source category
was also refined and updated based on better information. For many MACT
standards, we now have lists of regulated facilities, which allows for
better designation of major facilities in the inventory.
We received several comments requesting that the area source
categories designated as ``SIC combined'' be broken down into
individual SIC (or Standard Industrial Classification) codes. Examples
of these source categories from the draft Strategy were Electronic and
other Electric Equipment Manufacturing (SICs combined), Food Products
(SICs combined) and Instruments and Related Products (SICs combined).
The way in which the SIC codes were combined didn't reflect a technical
analysis of whether these SIC codes could in fact be combined into
single source categories for regulatory purposes. In general, the
combinations included large numbers of different industry types which
would later have to be broken down into separate projects and separate
source categories for regulation. In addition, it was difficult to
discern from the list which subsets of the multiple SIC codes were
actually emitting the pollutants of concern and would eventually be
subject to regulation.
For the final Strategy, we listed source categories (presented in
Table 3) that primarily represent single SIC codes in order to more
accurately identify the sources that may ultimately be subject to
regulation. The exception to this is when the source category was
derived directly from information obtained during the development of a
section 112(d) standard (e.g., Paint Stripping Operations), in which
case the area source category described for the standard may
incorporate multiple SIC codes.
Despite these improvements in the baseline, there are still
uncertainties in the emissions reported in some categories and in some
of the TRI reporting. Our awareness of these uncertainties is based on
our improved knowledge of some source categories and emission
estimation methods, and also on an improved recognition of the limits
of our data for other source categories. For the development of the
area source category listing, we needed to use the baseline inventory
information on a more refined scale (at the source category level) than
we did in development of the HAPs list where we used the baseline
inventory on a national scale. For this reason, we sometimes modified
the individual source category information in various ways, such as by
combining source categories' emission information. In a few cases, we
changed the emission information related to tonnage for some source
categories. These adjustments to tonnage didn't affect the total
emissions used on a national scale. As a result of these changes, the
information presented in the area source category analysis (source
category names and tonnage) may not always match the way source
categories are presented in the final baseline inventory.
Examples of some changes made in the area source category analysis
include combining all the emissions from human and animal cremation,
because they will be addressed under one rulemaking (Other Solid Waste
Incinerators). For the same reason, we combined all the emissions from
institutional and commercial heating, as this will be addressed under
one rulemaking (Institutional/Commercial Boilers). We also included the
area emission estimates for the source category Paint Stripping
Operations, because they were inadvertently excluded from the final
baseline inventory. We changed the name of the source category listed
as Chlorine Production in the baseline to Mercury Cell Chlor-Alkali
Plants. This revised source category name better represents the portion
of the industry which will be ``subject to standards''. Additional
changes are described in the technical support document for identifying
area source categories.
As discussed in section II.A.2., several of the 30 area source HAPs
listed in the draft Strategy have been replaced based on updated
information. The result is the addition of the following HAPs to the
list of 30 area source HAPs: beryllium compounds, hexachlorobenzene,
polychlorinated biphenyls (PCBs), quinoline, vinyl chloride, and
1,1,2,2,-tetrachloroethane. Quinoline was included in the draft
Strategy list for major sources only, but based on updated information
is now included for area sources. These changes in the area source HAPs
list have also led to changes in the area source categories list.
3. Area Source Category Selection Approach in Final Strategy
We've reviewed the provisions in sections 112(c)(3) and
112(k)(3)(B)(ii), and believe the most reasonable interpretation of the
Act is still the interpretation adopted in the draft Strategy. In order
to comply with the requirements of both sections, we must list those
source categories representing 90 percent of the emissions of each of
the 30 area source HAPs.
We have, however, changed our criteria for selecting the source
categories contributing to emissions of the 30 area source HAPs. Again
we've adopted a two-step approach with the first step being similar to
that in the draft Strategy. In the first step we've identified area
sources that contribute to emissions of the 30 area source HAPs, and
that are subject to existing standards, or will be subject to standards
that are currently being developed. These area source categories have
already been listed for regulation under the Act. As in the draft
Strategy, for each of these source categories we identified the percent
contribution to the total area source emissions for each of the 30 area
source HAPs.
In the second step, we've decided, at this time, to add only those
area source categories that contribute at least 15 percent of the total
area source emissions of any of the individual area source HAPs to the
list of source categories. We've adopted this criterion to account for
the uncertainties in our current inventory data. While we've been able
to significantly improve our baseline emissions inventory data, data
gaps and uncertainty still remain. This is particularly true as we move
to a more refined scale to determine emissions at a source category
level. As a result, we've decided to only list new categories of area
sources at this time if the inventory data demonstrate that each newly
listed area source category contributes at least 15 percent to the
national urban emissions of at least one of the 30 area source HAPs.
Once listed, we've counted the percent contribution, even if less than
15 percent, to emissions of any other area source HAPs, because once
the source is subject to regulation its emissions of any of the 30 area
source HAPs can be counted toward the 90-percent goal for each of the
area source HAPs. Likewise, when we subject these source categories to
regulation we'll evaluate regulation of all 188 HAPs, not just the 33
urban HAPs listed under this Strategy.
The result of these new criteria for the source selection process
is that the current list doesn't, at this time, contain area source
categories representing 90 percent of the emissions of each individual
HAP. It's important to make clear that we still intend to meet our
statutory obligation to list area sources accounting for 90 percent of
the emissions of each of the 30 area source HAPs. We've chosen to
complete this list in stages, adding to, deleting from, or shuffling
the list as we gather more and improved data. This first stage lists
those area source categories that contribute at least 15 percent, and,
[[Page 38721]]
therefore, we're confident add real contributions to the total area
source emissions of a particular area source HAP. As discussed in
section IV.D., we'll be conducting an initial national risk assessment
in the spring of 2000 that will be used in part to prioritize which
standards to pursue first. This initial assessment will use the much
better-developed 1996 NTI. We'll use this information as part of our
process to reevaluate the source categories listed in the Strategy.
Based on this updated information, we may decide to remove an area
source category listed here if, for example, the reason for the listing
was inaccurate (e.g., faulty reporting to TRI) or if no urban area
sources exist. We'll also use this assessment to evaluate area source
categories to be added to the list.
We believe this iterative approach is consistent with the general
scheme for listing and regulating area sources under section 112 of the
Act. Section 112 establishes two distinct steps for regulating
emissions of HAPs--one for listing source categories under 112(c) and
one for setting standards under 112(d). Section 112(k) incorporates
this two-step approach. The source category listing step (see for
example, sections 112(c)(1) and (9)) is intended to be an ongoing
process. Under section 112(e)(4), listing of a particular source
category isn't considered final agency action until EPA issues emission
standards for that source category. Thus, we feel the list of area
source categories is flexible both for the addition of new area source
categories and/or removal of area source categories, through public
notice. We believe our current approach for fulfilling the 90-percent
requirements in sections 112(k)(3)(B) and 112(c)(3) is consistent with
the overall structure of section 112 which authorizes us to treat the
list of area source categories as a work in progress.
One alternative to this iterative approach would be to attempt to
list all sources accounting for 90 percent of the emissions of each
individual area source HAPs as we did in the draft Strategy, and to
make changes in the future as data are collected and improved. We
decided against this approach because it would involve listing many
area source categories contributing very small amounts of a particular
HAP based on data that we consider in many instances to still have
significant uncertainty despite numerous improvements. In the end, we
believe the two approaches aren't meaningfully different. Even if we
officially ``listed'' these small contributors, their status on the
list would be tentative at best. Under the current approach, we've
identified all of these small contributors in the supporting materials
for this rulemaking, but we've chosen not to list them under section
112(c)(3) at this time, if the emissions currently appear to be less
than 15 percent of the ![[logo] US EPA](http://www.epa.gov/epafiles/images/logo_epaseal.gif){kind=logo}