Clean Air Fine Particle Implementation Rule, 20586-20667 [E7-6347]

Agencies

• ENVIRONMENTAL PROTECTION AGENCY

[Federal Register Volume 72, Number 79 (Wednesday, April 25, 2007)]
[Rules and Regulations]
[Pages 20586-20667]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: E7-6347]



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Part II





Environmental Protection Agency





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40 CFR Part 51



Clean Air Fine Particle Implementation Rule; Final Rule



Agency Information Collection Activities: Proposed Collection; Comment 
Request; PM2.5 Ozone National Ambient Air Quality Standard 
Implementation Rule; EPA ICR No. 2258.01; Notice

Federal Register / Vol. 72, No. 79 / Wednesday, April 25, 2007 / 
Rules and Regulations

[[Page 20586]]


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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 51

[EPA-HQ-OAR-2003-0062; FRL-8295-2]
RIN 2060-AK74


Clean Air Fine Particle Implementation Rule

AGENCY: Environmental Protection Agency (EPA).

ACTION: Final rule.

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SUMMARY: This final action provides rules and guidance on the Clean Air 
Act (CAA) requirements for State and Tribal plans to implement the 1997 
fine particle (PM2.5) national ambient air quality standards 
(NAAQS). Fine particles and precursor pollutants are emitted by a wide 
range of sources, including power plants, cars, trucks, industrial 
sources, and other burning or combustion-related activities. Health 
effects that have been associated with exposure to PM2.5 
include premature death, aggravation of heart and lung disease, and 
asthma attacks. Those particularly sensitive to PM2.5 
exposure include older adults, people with heart and lung disease, and 
children.
    Air quality designations became effective on April 5, 2005 for 39 
areas (with a total population of 90 million) that were not attaining 
the 1997 PM2.5 standards. By April 5, 2008, each State 
having a nonattainment area must submit to EPA an attainment 
demonstration and adopted regulations ensuring that the area will 
attain the standards as expeditiously as practicable, but no later than 
2015. This rule and preamble describe the requirements that States and 
Tribes must meet in their implementation plans for attainment of the 
1997 fine particle NAAQS. (Note that this rule does not include final 
PM2.5 requirements for the new source review (NSR) program; 
the final NSR rule will be issued at a later date.)

DATES: This rule is effective on May 29, 2007.

ADDRESSES: The EPA has established a docket for this action under 
Docket ID EPA-HQ-OAR-2003-0062. All documents relevant to this action 
are listed in the Federal docket management system at 
www.regulations.gov. Although listed in the index, some information is 
not publicly available (e.g. Confidential Business Information or other 
information whose disclosure is restricted by statute). Certain other 
material, such as copyrighted material, is not placed on the Internet 
and will be publicly available only in hard copy form. Publicly 
available docket materials are available either electronically through 
www.regulations.gov or in hard copy format at the EPA Docket Center, 
EPA/DC, EPA West, Room 3334, 1301 Constitution Avenue, NW., Washington, 
DC. The Public Reading Room is open from 8:30 a.m. to 4:30 p.m., Monday 
through Friday, excluding legal holidays. The telephone number for the 
Public Reading Room is (202) 566-1744, and the telephone number for the 
Office of Air and Radiation Docket and Information Center is (202) 566-
1742. A variety of information and materials related to the fine 
particle NAAQS and implementation program are also available on EPA's 
Web site: https://www.epa.gov/air/particles.

FOR FURTHER INFORMATION CONTACT: For general information, contact Mr. 
Richard Damberg, U.S. Environmental Protection Agency, Office of Air 
Quality Planning and Standards, Mail Code C539-01, Research Triangle 
Park, NC 27711, phone number (919) 54l-5592 or by e-mail at: 
damberg.rich@epa.gov.

SUPPLEMENTARY INFORMATION:

General Information

A. Does this action apply to me?

    Entities potentially regulated by this action are State and local 
air quality agencies.

B. Where can I get a copy of this document and other related 
information?

    In addition to being available in the docket, an electronic copy of 
this final rule will also be available on the World Wide Web. Following 
signature by the EPA Administrator, a copy of this final rule will be 
posted at https://www.epa.gov/particles/actions.html.

C. How is the preamble organized?

I. Background
II. Elements of the Clean Air Fine Particle Implementation Rule
    A. Precursors and Pollutants Contributing to Fine Particle 
Formation
    B. No Classification System
    C. Due Dates and Basic Requirements for Attainment 
Demonstrations
    D. Attainment Dates
    E. Modeling and Attainment Demonstrations
    F. Reasonably Available Control Technology and Reasonably 
Available Control Measures
    G. Reasonable Further Progress
    H. Contingency Measures
    I. Transportation Conformity
    J. General Conformity
    K. Emission Inventory Requirements
    L. Condensable Particulate Matter Test Methods and Related Data 
Issues
    M. Improving Source Monitoring
    N. Guidance Specific to Tribes
    O. Enforcement and Compliance
    P. Emergency Episodes
    Q. Ambient Monitoring
III. Statutory and Executive Order Reviews
    A. Executive Order 12866: Regulatory Planning and Review
    B. Paperwork Reduction Act
    C. Regulatory Flexibility Act
    D. Unfunded Mandates Reform Act
    E. Executive Order 13132: Federalism
    F. Executive Order 13175: Consultation and Coordination With 
Indian Tribal Governments
    G. Executive Order 13045: Protection of Children From 
Environmental Health and Safety Risks
    H. Executive Order 13211: Actions That Significantly Affect 
Energy Supply, Distribution, or Use
    I. National Technology Transfer Advancement Act
    J. Executive Order 12898: Federal Actions To Address 
Environmental Justice in Minority Populations and Low-Income 
Populations
    K. Congressional Review Act
    L. Petitions for Judicial Review
    M. Judicial Review
IV. Statutory Authority

I. Background

    Fine particles in the atmosphere are comprised of a complex mixture 
of components. Common constituents include: sulfate (SO4); 
nitrate (NO3); ammonium; elemental carbon; a great variety 
of organic compounds; and inorganic material (including metals, dust, 
sea salt, and other trace elements) generally referred to as 
``crustal'' material, although it may contain material from other 
sources. Airborne particles generally less than or equal to 2.5 
micrometers in diameter are considered to be ``fine particles'' (also 
referred to as PM2.5). (A micrometer is one-millionth of a 
meter, and 2.5 micrometers is less than one-seventh the average width 
of a human hair.) ``Primary'' particles are emitted directly into the 
air as a solid or liquid particle (e.g., elemental carbon from diesel 
engines or fire activities, or condensable organic particles from 
gasoline engines). ``Secondary'' particles (e.g., sulfate and nitrate) 
form in the atmosphere as a result of various chemical reactions. 
(Section II of the proposed rule included detailed technical discussion 
on PM2.5, its precursors, formation processes, and emissions 
sources.)
    The EPA established air quality standards for PM2.5 
based on evidence from numerous health studies demonstrating that 
serious health effects are associated with exposures to elevated levels 
of PM2.5. Epidemiological studies have shown statistically 
significant correlations between elevated PM2.5 levels and 
premature mortality. Other important

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effects associated with PM2.5 exposure include aggravation 
of respiratory and cardiovascular disease (as indicated by increased 
hospital admissions, emergency room visits, absences from school or 
work, and restricted activity days), changes in lung function and 
increased respiratory symptoms, as well as new evidence for more subtle 
indicators of cardiovascular health. Individuals particularly sensitive 
to PM2.5 exposure include older adults, people with heart 
and lung disease, and children.
    On July 18, 1997, we revised the NAAQS for particulate matter (PM) 
to add new standards for fine particles, using PM2.5 as the 
indicator. We established health-based (primary) annual and 24-hour 
standards for PM2.5 (62 FR 38652).\1\ The annual standard 
was set at a level of 15 micrograms per cubic meter, as determined by 
the 3-year average of annual mean PM2.5 concentrations. The 
24-hour standard was set at a level of 65 micrograms per cubic meter, 
as determined by the 3-year average of the 98th percentile of 24-hour 
concentrations.
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    \1\ The original annual and daily standards for particles 
generally less than or equal to 10 micrometers in diameter (also 
referred to as PM10) were established in 1987. In the 
1997 PM NAAQS revision, EPA also revised the standards for 
PM10, but these revised PM10 standards were 
later vacated by the court, and the 1987 PM10 standards 
remained in effect. In the 2006 NAAQS revision, the 24-hour 
PM10 standard was retained but the annual standard was 
revoked. Today's implementation rule and guidance does not address 
PM10.
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    Attainment of the 1997 PM2.5 standards is estimated to 
lead to reductions in health impacts, including tens of thousands fewer 
premature deaths each year, thousands fewer hospital admissions and 
emergency room visits each year, hundreds of thousands fewer absences 
from work and school, and hundreds of thousands fewer respiratory 
illnesses in children annually. The EPA's evaluation of the science 
concluded that there was not sufficient information to either support 
or refute the existence of a threshold for health effects from PM 
exposure.\2\
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    \2\ Environmental Protection Agency. (2004a). Air Quality 
Criteria for Particulate Matter. Research Triangle Park, NC: 
National Center for Environmental Assessment--RTP, Office of 
Research and Development, U.S. Environmental Protection Agency, 
Research Triangle Park, NC 27711; report no. EPA/600/P-99/002aF and 
EPA/600/P-99/002bF. October 2004.
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    We subsequently completed in October 2006 another review of the 
NAAQS for PM. With regard to the primary standards, the 24-hour 
PM2.5 standard was strengthened to a level of 35 micrograms 
per cubic meter, based on the 3-year average of the 98th percentile of 
24-hour concentrations, and the level of the annual standard remained 
unchanged.\3\ Attainment of the 2006 PM2.5 standards is 
estimated to lead to additional reductions in health impacts, including 
approximately 1,200 to 13,000 fewer premature deaths each year, 1,630 
fewer hospital admissions and 1,200 fewer emergency room visits for 
asthma each year, 350,000 fewer absences from work and school, and 
155,300 fewer respiratory illnesses in children annually.\4\
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    \3\ The revised fine particle NAAQS were published on October 
17, 2006 (71 FR 61144). See EPA's Web site for additional 
information: https://www.epa.gov/pm/.
    \4\ Regulatory Impact Analysis for Particulate Matter National 
Ambient Air Quality Standards (September 2006), page ES-8. The 
mortality range includes estimates based on the results of an expert 
elicitation study, along with published epidemiological studies.
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    In both 1997 and 2006 EPA established welfare-based (secondary) 
standards identical to the levels of the primary standards. The 
secondary standards are designed to protect against major environmental 
effects of PM2.5 such as visibility impairment, soiling, and 
materials damage. The EPA also established the regional haze 
regulations in 1999 for the improvement of visual air quality in 
national parks and wilderness areas across the country. Because 
regional haze is caused primarily by light scattering and light 
absorption by fine particles in the atmosphere, EPA is encouraging the 
States to integrate their efforts to attain the PM2.5 
standards with those efforts to establish reasonable progress goals and 
associated emission reduction strategies for the purposes of improving 
air quality in our treasured natural areas under the regional haze 
program.
    The scientific assessments used in the development of the 
PM2.5 standards included a scientific peer review and public 
comment process. We developed scientific background documents based on 
the review of hundreds of peer-reviewed scientific studies. The Clean 
Air Scientific Advisory Committee, a congressionally mandated group of 
independent scientific and technical experts, provided extensive review 
of these assessments, and found that EPA's review of the science 
provided an adequate basis for the EPA Administrator to make a 
decision. More detailed information on health effects of 
PM2.5 can be found on EPA's Web site at: https://www.epa.gov/
air/urbanair/pm/. Additional information on EPA's scientific 
assessment documents supporting the 1997 standards are available at 
https://www.epa.gov/ttn/oarpg/t1cd.html; additional scientific 
assessment information on the 2006 standards is available at: https://
www.epa.gov/ttn/naaqs/standards/pm/s_pm_cr_cd.html.
    The EPA issued final PM2.5 designations for areas 
violating the 1997 standards on December 17, 2004. They were published 
in the Federal Register on January 5, 2005 (70 FR 944). On April 5, 
2005, EPA issued a supplemental notice which changed the designation 
status of eight areas from nonattainment to attainment based on newly 
updated 2002-2004 air quality data (70 FR 19844; published in the 
Federal Register on April 14, 2005). A total of 39 areas were 
designated as nonattainment for the 1997 PM2.5 standards. 
The population of these areas is estimated at about 90 million (or more 
than 30% of the U.S. population). Most of these areas only violate the 
annual standard, but a few violate both the annual and 24-hour 
standards.
    The nonattainment designation for an area starts the process 
whereby a State or Tribe must develop an implementation plan that 
includes, among other things, a demonstration showing how it will 
attain the ambient standards by the attainment dates required in the 
CAA. Under section 172(b), States have up to 3 years after EPA's final 
designations to submit their SIPs to EPA. These SIPs will be due on 
April 5, 2008, 3 years from the effective date of the designations.
    Section 172(a)(2) of the Act requires States to attain the 
standards as expeditiously as practicable but within 5 years of 
designation (i.e. attainment date of April 2010 based on air quality 
data for 2007-2009), or within up to 10 years of designation (i.e. to 
April 2015) if the EPA Administrator extends an area's attainment date 
by 1-5 years based upon the severity of the nonattainment problem or 
the feasibility of implementing control measures.
    Virtually all nonattainment problems appear to result from a 
combination of local emissions and transported emissions from upwind 
areas. The structure of the CAA requires EPA to develop national rules 
for certain types of sources which are also significant contributors to 
local air quality problems, including motor vehicles and fuels. It also 
provides for States to address emissions sources on an area-specific 
basis through such requirements as RACT, RACM, and RFP.
    We believe that to attain the PM2.5 standards, it is 
important to pursue emissions reductions simultaneously on the local, 
regional, and national levels. The EPA issued the Clean Air Interstate

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Rule (CAIR) \5\ on March 10, 2005 to address the interstate transport 
of sulfur dioxide and nitrogen oxide emissions primarily from power 
plants. Section 110 gives EPA the authority to require SIPs to 
``prohibit * * * any source or other type of emission activity within 
the State from emitting any air pollutant in amounts which will 
contribute significantly to nonattainment in, or interfere with 
maintenance by, any other State with respect to'' any NAAQS, and to 
prohibit sources or emission activities from emitting pollutants in 
amounts which will interfere with measures required to be included in 
State plans to prevent significant deterioration of air quality or to 
protect visibility (such as the protection of 156 mandatory Federal 
class I areas under the regional haze rule \6\). CAIR employs the same 
emissions trading approach used to achieve cost-effective emission 
reductions under the acid rain program. It outlines a two-phase program 
with increasingly tighter power plant emissions caps for 28 eastern 
states and the District of Columbia: SO2 caps of 3.6 million 
tons in 2010, and 2.5 million in 2015; NOX caps of 1.5 in 
2009 and 1.3 in 2015; and NOX ozone season caps of 580,000 
tons in 2009 and 480,000 tons in 2015. Emission caps are divided into 
State SO2 and NOX budgets. By the year 2015, the 
Clean Air Interstate Rule is estimated to result in:
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    \5\ See https://www.epa.gov/cair.
    \6\ See 64 FR 35714, July 1, 1999.

--$85 to $100 billion in annual health benefits, including preventing 
17,000 premature deaths, millions of lost work and school days, and 
tens of thousands of non-fatal heart attacks and hospital admissions 
annually.
--Nearly $2 billion in annual visibility benefits in southeastern 
national parks, such as Great Smoky and Shenandoah.
--Significant regional reductions in sulfur and nitrogen deposition, 
reducing the number of acidic lakes and streams in the eastern U.S.

    Over the past several years, EPA has also issued a number of 
regulations addressing emissions standards for new cars, trucks and 
buses. These standards are providing reductions in motor vehicle 
emissions of volatile organic compounds (VOCs, also referred to as 
hydrocarbons), NOX, and direct PM emissions (such as 
elemental carbon) as older vehicles are retired and replaced. Other 
existing rules are designed to reduce emissions from several categories 
of nonroad engines. The Tier 2 motor vehicle emission standards, 
together with the associated requirements to reduce sulfur in gasoline, 
are estimated to provide additional benefits nationally beginning in 
2004.\7\ When the new tailpipe and sulfur standards are fully 
implemented, Americans are estimated to benefit from the clean-air 
equivalent of removing 164 million cars from the road. These new 
standards require passenger vehicles to have emissions 77 to 95 percent 
cleaner than those on the road today and require fuel manufacturers to 
reduce the sulfur content of gasoline by up to 90 percent. In addition, 
the 2001 heavy-duty diesel engine regulations \8\ will lead to 
continued emissions reductions as older vehicles in that engine class 
are retired and fleets turn over. New emission standards began to take 
effect for model year 2007 and apply to heavy-duty highway engines and 
vehicles. These standards are based on the use of high-efficiency 
catalytic exhaust emission control devices or comparably effective 
advanced technologies. Because these devices are damaged by sulfur, the 
level of sulfur in highway diesel fuel was to be reduced by 97 percent 
by mid-2006. We project a 2.6 million ton reduction of NOX 
emissions in 2030 when the current heavy-duty vehicle fleet is 
completely replaced with newer heavy-duty vehicles that comply with 
these emission standards. By 2030, we estimate that this program will 
reduce annual emissions of hydrocarbons by 115,000 tons and PM by 
109,000 tons. These emissions reductions are on par with those that we 
anticipate from new passenger vehicles and low sulfur gasoline under 
the Tier 2 program.
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    \7\ See Tier II emission standards at 65 FR 6698, February 10, 
2000.
    \8\ See heavy-duty diesel engine regulations at 66 FR 5002, 
January 18, 2001.
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    The EPA also finalized national rules in May 2004 to reduce 
significantly PM2.5 and NOX emissions from 
nonroad diesel-powered equipment.\9\ These nonroad sources include 
construction, agricultural, and industrial equipment, and their 
emissions constitute an important fraction of the inventory for direct 
PM2.5 emissions (such as elemental carbon and organic 
carbon), and NOX. The EPA estimates that affected nonroad 
diesel engines currently account for about 44 percent of total diesel 
PM emissions and about 12 percent of total NOX emissions 
from mobile sources nationwide. These proportions are even higher in 
some urban areas. The diesel emission standards will reduce emissions 
from this category by more than 90 percent, and are similar to the 
onroad engine requirements implemented for highway trucks and buses. 
Because the emission control devices can be damaged by sulfur, EPA also 
established requirements to reduce the allowable level of sulfur in 
nonroad diesel fuel by more than 99 percent by 2010. In 2030, when the 
full inventory of older nonroad engines has been replaced, the nonroad 
diesel program will annually prevent up to 12,000 premature deaths, one 
million lost work days, 15,000 heart attacks and 6,000 children's 
asthma-related emergency room visits.
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    \9\ For more information on the proposed nonroad diesel engine 
standards, see EPA's Web site: https://www.epa.gov/nonroad/.
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    The EPA expects the implementation of regional and national 
emission reduction programs such as CAIR and the suite of mobile source 
rules described above to provide significant air quality improvements 
for PM2.5 nonattainment areas. At the same time, analyses 
for the final CAIR rule indicate that without implementation of local 
measures, a number of PM2.5 areas are projected to remain in 
nonattainment status in the 2010-2015 timeframe. Thus, EPA believes 
that local and State emission reduction efforts will need to play an 
important role in addressing the PM2.5 problem as well. The 
EPA will work closely with States, Tribes, and local governments to 
develop appropriate in-state pollution reduction measures to complement 
regional and national strategies to meet the standards expeditiously 
and in a cost-effective manner. States will need to evaluate 
technically and economically feasible emission reduction opportunities 
and determine which measures can be reasonably implemented in the near 
term. Local and regional emission reduction efforts should proceed 
concurrently and expeditiously.
    The promulgation of a revised 24-hour PM2.5 standard 
effective on December 18, 2006 has initiated another process of State 
recommendations, and the eventual designation by EPA of areas not 
attaining the revised standard. The additional designations are to be 
completed within two years from the effective date, although EPA may 
take an additional year to complete the designations if it determines 
it does not have sufficient information. State plans to attain the 24-
hour standard would then be due within three years of the final 
designations. A number of areas, including some that are already 
designated as not attaining the 1997 standards, may be exceeding the 
revised 24-hour standard. The EPA encourages State and local 
governments to be mindful of the strengthened 24-hour standard as they 
adopt emission reduction strategies to attain the 1997 standards. Such 
steps may help with

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future attainment efforts, or even help some areas avoid a 
nonattainment designation for the 24-hour standard in the first place.
    The public health benefits of meeting the PM2.5 
standards are estimated to be significant. Even small reductions in 
PM2.5 levels may have substantial health benefits on a 
population level. For example, in a moderate-sized metropolitan area 
with a design value of 15.5 [mu]g/m3, efforts to improve annual average 
air quality down to the level of the standard (15.0 [mu]g/m3) are 
estimated to result in as many as 25-50 fewer mortalities per year due 
to air pollution exposure. In a smaller city, the same air quality 
improvement from 15.5 to 15.0 [mu]g/m3 still are estimated to result in 
a number of avoided mortalities per year. These estimates are based on 
EPA's standard methodology for calculating health benefits as used in 
recent rulemakings.\10\ In addition, because many different precursors 
contribute to the formation of fine particles, reductions in pollutants 
that contribute to PM2.5 also can provide concurrent 
benefits in addressing a number of other air quality problems--such as 
ground-level ozone, regional haze, toxic air pollutants, and urban 
visibility impairment.
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    \10\ See: U.S. EPA 2006. Regulatory Impact Analysis for the 
Particulate Matter National Ambient Air Quality Standards. Air 
Benefits and Cost Group, Office of Air Quality Planning and 
Standards, Research Triangle Park, N.C. October 6, 2006. Appendix A 
provides an analysis of estimated benefits and costs of attaining 
the 1997 PM NAAQS standards in 2015.
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    In order to assist States in developing effective plans to address 
the local component of the PM2.5 nonattainment problem, EPA 
is issuing this final fine particle implementation rule. The EPA is 
issuing this rule to implement the 1997 PM2.5 NAAQS in 
accordance with the statutory requirements of the CAA set forth in 
Subpart 1 of Part D of Title 1, i.e., sections 171-179B of the Act. The 
EPA believes that the CAA directs the Agency to implement new or 
revised NAAQS in nonattainment areas solely in accordance with Subpart 
1, unless another Subpart of the Act also applies to the particular 
NAAQS at issue. In this case, EPA has concluded that Congress did not 
intend the Agency to implement particulate matter NAAQS other than 
those using PM10 as the indicator in accordance with Subpart 
4 of Part D of Title 1, i.e., sections 188-190 of the CAA. Moreover, 
EPA believes that implementation of the PM2.5 NAAQS under 
the provisions of Subpart 1 is more appropriate, given the inherent 
nature of the PM2.5 nonattainment problem. In contrast to 
PM10, EPA anticipates that achieving the NAAQS for 
PM2.5 will generally require States to evaluate different 
sources for controls, to consider controls of one or more precursors in 
addition to direct PM emissions, and to adopt different control 
strategies. As a result, EPA has concluded that the provisions of 
Subpart 1 will allow States and EPA to tailor attainment plans so that 
they can be based more specifically upon the facts and circumstances of 
each nonattainment area.
    The proposed clean air fine particle implementation rule was issued 
on November 1, 2005 (70 FR 65984). About 100 comments were received 
from private citizens and parties representing industry, state and 
local governments, environmental groups, and federal agencies. Section 
II of this document describes the primary elements of the fine particle 
implementation program. Each section summarizes the relevant policies 
and options discussed in the proposed rule, discusses the final policy 
set forth by EPA in the final rule, and provides responses to the major 
comments received on each issue.

II. Elements of the Clean Air Fine Particle Implementation Rule

A. Precursors and Pollutants Contributing to Fine Particle Formation

1. Introduction
    The main precursor gases associated with fine particle formation 
are SO2, NOX, volatile organic compounds (VOC), 
and ammonia. This section provides technical background on each 
precursor, discusses the policy approach for addressing each precursor 
under the PM2.5 implementation program, and responds to key 
issues raised in the public comment process. A subsection is also 
included on direct PM2.5 emissions to address key comments 
received on this issue as well.
    Gas-phase precursors SO2, NOX, VOC, and 
ammonia undergo chemical reactions in the atmosphere to form secondary 
particulate matter. Formation of secondary PM depends on numerous 
factors including the concentrations of precursors; the concentrations 
of other gaseous reactive species; atmospheric conditions including 
solar radiation, temperature, and relative humidity (RH); and the 
interactions of precursors with preexisting particles and with cloud or 
fog droplets. Several atmospheric aerosol species, such as ammonium 
nitrate and certain organic compounds, are semivolatile and are found 
in both gas and particle phases. Given the complexity of PM formation 
processes, new information from the scientific community continues to 
emerge to improve our understanding of the relationship between sources 
of PM precursors and secondary particle formation.
    As an initial matter, it is helpful to clarify the terminology we 
use throughout this notice to discuss precursors. We recognize 
NOX, SO2, VOCs, and ammonia as precursors of 
PM2.5 in the scientific sense because these pollutants can 
contribute to the formation of PM2.5 in the ambient air. In 
section II.K on emission inventory issues, we make the point that 
because of the complex and variable interaction of multiple pollutants 
and precursors in the formation of fine particles, it is important for 
States and EPA to continue to characterize and improve the emissions 
inventories for all PM2.5 precursors. The States and EPA 
need to use the best available information available in conducting air 
quality modeling and other assessments. At the same time, the 
refinement of emissions inventories, the overall contribution of 
different fine particle precursors to PM2.5 formation, and 
the efficacy of alternative potential control measures will vary by 
location. This requires that we further consider in this action how 
States should address these PM2.5 precursors in their 
PM2.5 attainment plan programs. Thus, we require emission 
inventories to include the best available information on all pollutants 
and precursors that contribute to PM2.5 concentrations, and 
at same time we use the term ``PM2.5 attainment plan 
precursor'' to describe only those precursors that are required to be 
evaluated for control strategies in a specific PM2.5 
nonattainment area or maintenance area plan.
    In this rule, EPA has not made a finding that all precursors should 
be evaluated for possible controls in each specific nonattainment area. 
The policy approach in the rule instead requires sulfur dioxide to be 
evaluated for control measures in all areas, and describes general 
presumptive policies for NOX, ammonia, and VOC for all 
nonattainment areas. The rule provides a mechanism by which the State 
and/or EPA can make an area-specific demonstration to reverse the 
general presumption for these three precursors. States must also 
consider any relevant information brought forward by interested parties 
in the SIP planning and development process. (See section II.A.8 for 
additional discussion on these issues.)
    In the following sections, we discuss how States must evaluate 
PM2.5 precursors for nonattainment program issues in 
PM2.5 implementation plans,

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including issues such as RACT, RACM, and reasonable further progress. 
This discussion in the final rule is linked to precursor policies for 
the implementation of the new source review program, the transportation 
conformity program, the general conformity program, and the regional 
haze program. All of these programs take effect prior to approval of 
SIPs for attaining the PM2.5 NAAQS. In the case of NSR, the 
program applies on the effective date of the nonattainment area 
designation. In the case of transportation conformity and general 
conformity, the program takes effect 1 year from the effective date of 
designation of the nonattainment area (i.e., April 5, 2006 for areas 
designated nonattainment effective April 5, 2005). Thus, for each of 
these programs there is an interim period between the date the program 
becomes applicable to a given nonattainment area and the date the State 
receives EPA approval of its overall PM2.5 implementation 
plan.
2. Legal Authority to Regulate Precursors
 a. Background
    The CAA authorizes the Agency to regulate criteria pollutant 
precursors. The term ``air pollutant'' is defined in section 302(g) to 
include ``any precursors to the formation of any air pollutant, to the 
extent the Administrator has identified such precursor or precursors 
for the particular purpose for which the term `air pollutant' is 
used.'' The first clause of this second sentence in section 302(g) 
explicitly authorizes the Administrator to identify and regulate 
precursors as air pollutants under other parts of the CAA. In addition, 
the second clause of the sentence indicates that the Administrator has 
discretion to identify which pollutants should be classified as 
precursors for particular regulatory purposes. Thus, we do not 
necessarily construe the CAA to require that EPA identify a particular 
precursor as an air pollutant for all regulatory purposes where it can 
be demonstrated that various CAA programs address different aspects of 
the air pollutant problem. Likewise, we do not interpret the CAA to 
require that EPA treat all precursors of a particular pollutant the 
same under any one program when there is a basis to distinguish between 
such precursors. For example, in a rule addressing PM2.5 
precursors for purposes of the transportation conformity program, we 
chose to adopt a different approach for one precursor based on the 
limited emissions of that precursor from onroad mobile sources and the 
degree to which it contributes to PM2.5 concentrations. (70 
FR 24280; May 6, 2005).
    Other provisions of the CAA reinforce our reading of section 302(g) 
that Congress intended precursors to NAAQS pollutants to be subject to 
the air quality planning and control requirements of the CAA, but also 
recognized that there may be circumstances where it is not appropriate 
to subject precursors to certain requirements of the CAA. Section 182 
of the CAA provides for the regulation of NOX and VOCs as 
precursors to ozone in ozone nonattainment areas, but also provides in 
section 182(f) that major stationary sources of NOX (an 
ozone precursor) are not subject to emission reductions controls for 
ozone where the State shows through modeling that NOX 
reductions do not decrease ozone. Section 189(e) provides for the 
regulation of PM10 precursors in PM10 
nonattainment areas, but also recognizes that there may be certain 
circumstances (e.g. if precursor emission sources do not significantly 
contribute to PM10 levels) where it is not appropriate to 
apply control requirements to PM10 precursors. The 
legislative history of Section 189(e) recognized the complexity behind 
the science of precursor transformation into PM10 ambient 
concentrations and the need to harmonize the regulation of 
PM10 precursors with other provisions of the CAA:

    The Committee notes that some of these precursors may well be 
controlled under other provisions of the CAA. The Committee intends 
that * * * the Administrator will develop models, mechanisms, and 
other methodology to assess the significance of the PM10 
precursors in improving air quality and reducing PM10. 
Additionally, the Administrator should consider the impact on ozone 
levels of PM10 precursor controls. The Committee expects 
the Administrator to harmonize the PM10 reduction 
objective of this section with other applicable regulations of this 
CAA regarding PM10 precursors, such as NOX. 
See H. Rpt. 101-490, Pt. 1, at 268 (May 17, 1990), reprinted in S. 
Prt. 103-38, Vol. II, at 3292.

    In summary, section 302(g) of the CAA clearly calls for the 
regulation of precursor pollutants, but the CAA also identifies 
circumstances when it may not be appropriate to regulate precursors and 
gives the Administrator discretion to determine how to address 
particular precursors under various programs required by the CAA. Due 
to the complexities associated with precursor emissions and their 
variability from location to location, we believe that in certain 
situations it may not be effective or appropriate to control a certain 
precursor under a particular regulatory program or for EPA to require 
similar control of a particular precursor in all areas of the country.
b. Final Rule
    The final rule maintains the same legal basis for regulating 
precursors as was described in the proposal and in the background 
section above. We also include a clarification of the term 
``significant contributor.''
    In the proposal, when considering the impacts of the precursors 
NOX, VOC and ammonia on ambient concentrations of 
particulate matter, we referred to the possibility of reversing the 
presumed approach for regulating or not regulating a precursor if it 
can be shown that the precursor in question is or is not a 
``significant contributor'' to PM2.5 concentrations within 
the specific nonattainment area. ``Significant contribution'' in this 
context is a different concept than that in Section 110(a)(2)(D). 
Section 110(a)(2)(D) prohibits States from emitting air pollutants in 
amounts which significantly contribute to nonattainment or other air 
quality problems in other states. Consistent with the discussion of 
sections 189(e) and 302(g) above, we are clarifying that the use in 
this implementation rule of the term ``significant contribution'' to 
the nonattainment area's PM2.5 concentration means that a 
significant change in emissions of the precursor from sources in the 
state would be projected to provide a significant change in 
PM2.5 concentrations in the nonattainment area. For example, 
if modeling indicates that a reduction in a state's NOX 
emissions would reduce ambient PM2.5 levels in the 
nonattainment area, but that a reduction in ammonia emissions would 
result in virtually no change in ambient PM2.5 levels, this 
would suggest that NOX is a significant contributor but that 
ammonia is not. The EPA in this rule is not establishing a quantitative 
test for determining whether PM2.5 levels in a nonattainment 
area change significantly in response to reductions in precursor 
emissions in a state. However, in considering this question, it is 
relevant to consider that relatively small reductions in 
PM2.5 levels are estimated to result in worthwhile public 
health benefits.
    This approach to identifying a precursor for regulation reflects 
atmospheric chemistry conditions in the area and the magnitude of 
emissions of the precursor in the area or State. Assessments of which 
source categories are more cost effective or technically feasible to 
control should be part of the later RACT and RACM assessment, to

[[Page 20591]]

occur after the basic assessment of which precursors are to be 
regulated is completed.
    In the proposed regulatory text, the provisions for reversing 
presumptions for NOX, VOC and ammonia included consideration 
of whether the precursor would significantly contribute to ``other 
downwind air quality concerns.'' In the final rule we have removed that 
language to clarify that identification of attainment plan precursors 
involves evaluation of the impact on PM2.5 levels in a 
nonattainment area of precursor emissions from sources within the 
state(s) where the nonattainment area is located. Other parts of the 
Act, notably section 110(a)(2)(D) and section 126, focus on interstate 
transport of pollutants.
c. Comments and Responses
    Comment: The EPA received several comments supporting EPA's 
interpretation of 302(g) to determine the appropriate regulatory status 
of each precursor pollutant.
    Response: The EPA agrees with the commenters. In establishing 
section 302(g), Congress intended that precursors to NAAQS pollutants 
be subject to the air quality planning and control requirements of the 
CAA. However, the CAA also recognizes that there may be circumstances 
where it is not appropriate to subject precursors to certain 
requirements of the CAA.
    Comment: The EPA received several comments regarding the 
applicability of section 189(e), noting that it requires states to 
presumptively control sources of PM10 precursors except 
where the EPA ``determines that such sources [of precursors] do not 
significantly contribute to PM10 levels which exceed the 
standard in the area.'' Several commenters stated that EPA does not 
have the legal authority to regulate PM2.5 precursors in a 
different manner. Several commenters maintained that all 
PM2.5 precursors presumptively should be subject to 
regulation unless demonstrated by the State as not a significant 
contributor to PM2.5 concentrations in a specific area.
    Response: As stated above, EPA believes that section 302(g) allows 
the Administrator to presumptively not require certain precursors to be 
addressed in PM2.5 implementation plans generally, while 
allowing the State or EPA to make a finding for a specific area to 
override the general presumption. In the following pollutant-specific 
sections of this preamble, EPA finds that at this time there is 
sufficient uncertainty regarding whether certain precursors 
significantly contribute to PM2.5 concentrations in all 
nonattainment areas such that the policy set forth in this rule does 
not presumptively require certain precursors (ammonia, VOC) to be 
controlled in each area. However, the State or EPA may reverse the 
presumption and regulate a precursor if it provides a demonstration 
showing that the precursor is a significant contributor to 
PM2.5 concentrations in the area. In addition, if in the 
State's SIP planning and adoption process a commenter provides 
additional information suggesting an alternative policy for regulating 
a particular precursor, the State will need to respond to this 
information in its rulemaking action.
3. Policy for Ammonia
    [Section II.E.2 of November 1, 2005 proposed rule (70 FR 65999); 
sec. 51.1002 in draft and final regulatory text.]
a. Background
    Ammonia (NH3) is a gaseous pollutant that is emitted by 
natural and anthropogenic sources. Emissions inventories for ammonia 
are considered to be among the most uncertain of any species related to 
PM. Ammonia serves an important role in neutralizing acids in clouds, 
precipitation and particles. In particular, ammonia neutralizes 
sulfuric acid and nitric acid, the two key contributors to acid 
deposition (acid rain). Deposited ammonia also can contribute to 
problems of eutrophication in water bodies, and deposition of ammonium 
particles may effectively result in acidification of soil as ammonia is 
taken up by plants. The NARSTO Fine Particle Assessment \11\ indicates 
that reducing ammonia emissions where sulfate concentrations are high 
may reduce PM2.5 mass concentrations, but may also increase 
the acidity of particles and precipitation. An increase in particle 
acidity is suspected to be linked with human health effects and with an 
increase in the formation of secondary organic compounds. Based on the 
above information and further insights gained from the NARSTO Fine 
Particle Assessment, it is apparent that the formation of particles 
related to ammonia emissions is a complex, nonlinear process.
---------------------------------------------------------------------------

    \11\ NARSTO (2004) (Particulate Matter Assessment for Policy 
Makers: A NARSTO Assessment. P. McMurry, M. Shepherd, and J. 
Vickery, eds. Cambridge University Press, Cambridge, England. ISBN 0 
52 184287 5.
---------------------------------------------------------------------------

    Though recent studies have improved our understanding of the role 
of ammonia in aerosol formation, ongoing research is required to better 
describe the relationships between ammonia emissions, particulate 
matter concentrations, and related impacts. The control techniques for 
ammonia and the analytical tools to quantify the impacts of reducing 
ammonia emissions on atmospheric aerosol formation are both evolving. 
Also, area-specific data are needed to evaluate the effectiveness of 
reducing ammonia emissions on reducing PM2.5 concentrations 
in different areas, and to determine where ammonia decreases may 
increase the acidity of particles and precipitation.
    The proposal showed consideration for the uncertainties about 
ammonia emissions inventories and about the potential efficacy of 
ammonia control measures by providing for a case-by-case approach. It 
was recommended that each State should evaluate whether reducing 
ammonia emissions would lead to PM2.5 reductions in their 
specific PM2.5 nonattainment areas. The proposed policy did 
not require States to address ammonia as a PM2.5 attainment 
plan precursor, unless a technical demonstration by the State or EPA 
showed that ammonia emissions from sources in the State significantly 
contribute to PM2.5 concentrations in a given nonattainment 
area or to other downwind air quality concerns. Where the State or EPA 
has determined that ammonia is a significant contributor to 
PM2.5 formation in a nonattainment area, the State would be 
required to evaluate control measures for ammonia emissions in its 
nonattainment SIP due in 2008, in the implementation of the PM program, 
and in other associated programs in that area.
b. Final Rule
    In the final rule, ammonia is presumed not to be a PM2.5 
attainment plan precursor, meaning that the State is not required to 
address ammonia in its attainment plan or evaluate sources of ammonia 
emissions for reduction measures. This presumption can be reversed 
based on an acceptable technical demonstration for a particular area by 
the State or EPA. If a technical demonstration by the State or EPA 
shows that ammonia emissions from sources in the State significantly 
contribute to PM2.5 concentrations in a given nonattainment 
area, the State must then evaluate and consider control strategies for 
reducing ammonia emissions in its nonattainment SIP due in 2008, in the 
implementation of the PM2.5 program. Technical 
demonstrations on ammonia should also consider the potential for 
atmospheric and particle acidity to increase with ammonia reductions. 
Further discussion about technical demonstrations to

[[Page 20592]]

support reversing a PM2.5 precursor presumption is included 
in section II.A.8 below.
    This approach was retained from the proposal because of continued 
uncertainties regarding ammonia emission inventories and the effects of 
ammonia emission reductions. Ammonia emission inventories are presently 
very uncertain in most areas, complicating the task of assessing 
potential impacts of ammonia emissions reductions. In addition, data 
necessary to understand the atmospheric composition and balance of 
ammonia and nitric acid in an area are not widely available across 
PM2.5 nonattainment areas, making it difficult to predict 
the results of potential ammonia emission reductions. Ammonia 
reductions may be effective and appropriate for reducing 
PM2.5 concentrations in selected locations, but in other 
locations such reductions may lead to minimal reductions in 
PM2.5 concentrations and increased atmospheric acidity. 
Research projects continue to expand our collective understanding of 
these issues, but at this time EPA believes this case-by-case policy 
approach is appropriate. In light of these uncertainties, we encourage 
States to continue efforts to better understand the role of ammonia in 
its fine particle problem areas.
c. Comments and Responses
    Comment: One commenter stated that scientific understanding of the 
complexities of PM formation from ammonia is limited. The commenter 
claimed that the reduction of ammonia will not reduce PM in many areas, 
and speciated PM data to investigate the potential decrease in PM from 
ammonia emissions reductions is not available in all areas.
    Response: The final rule takes these uncertainties into 
consideration by allowing ammonia to be addressed on a case-by-case 
basis. For any area about which enough information is available to 
determine that ammonia emission reductions would lead to a beneficial 
reduction in PM2.5, the State can develop a technical 
demonstration justifying the control of ammonia. If the State chooses 
to develop such a demonstration, preferably it should be completed as 
part of the SIP development process and prior to the adoption of 
control measures, in consultation with the appropriate EPA regional 
office.
    Comment: Some commenters claimed that requiring no action on some 
precursors is counter to the requirement in sections 172(a)(2) and 188 
to attain the NAAQS as expeditiously as practicable. They also asserted 
that presuming that ammonia is not a PM2.5 attainment plan 
precursor violates 302(g) by improperly delegating authority to the 
States.
    Response: In many areas, reducing ammonia emissions could have 
little effect on PM2.5 concentrations and could lead to the 
potentially harmful effect of increased atmospheric acidity. While 
States are not required to take action on ammonia sources under this 
policy, States would be required to address information on ammonia 
brought to their attention during the planning and rule adoption 
process. Under this approach, States should assess whether ammonia 
reductions would lead to reduced PM2.5 concentrations in 
specific nonattainment areas. If the State decides that ammonia 
reductions could yield beneficial reductions in PM2.5, the 
State should complete a technical demonstration supporting a reversal 
of the presumption. The EPA does not believe that this approach 
improperly delegates authority to the States. It establishes a general 
presumption for all areas through this rulemaking process, and allows 
for the presumption to be modified by the State or EPA on a case-by-
case basis. EPA still retains the ability to make a technical 
demonstration for any area if appropriate to reverse the presumption 
and require ammonia to be addressed in its attainment plan.
    Comment: Some commenters stated that the results of a large study 
on air emissions from concentrated animal feeding operations (CAFOs) 
should be evaluated before requiring control of ammonia in areas where 
agriculture is alleged to be a major source.
    Response: The $15 million national CAFO consent agreement study 
coordinated by Purdue University will greatly improve ammonia and VOC 
emissions inventories and our understanding of the impacts of 
agricultural emissions on particle formation. The EPA recognizes that 
the agricultural emissions study is expected to provide data for future 
planning purposes, and we expect that some of the results of the study 
will not be available in time to be considered in the development of 
PM2.5 State Implementation Plans dues in April 2008. 
However, if a State believes it has sufficient technical information to 
warrant regulation of ammonia emissions in their 2008 implementation 
plans, it may include in its plan a demonstration to reverse the 
presumption as well as emission reduction measures. The EPA will review 
each submittal on a case-by-case basis.
    Comment: A presumption to not address ammonia will impede certain 
states (i.e. those that have provisions requiring their regulations to 
be ``no stricter than Federal'' provisions) from regulating ammonia.
    Response: This presumptive approach to ammonia will not restrict 
States from addressing ammonia in their PM2.5 attainment 
plans. If a State has information indicating that reductions in ammonia 
emissions would cause beneficial reductions in PM2.5 
concentrations, the State can make a technical demonstration to reverse 
the presumption. In such cases, inclusion of ammonia as a 
PM2.5 attainment plan precursor would not be considered 
stricter than Federal requirements. Under the policy in the final rule, 
the Federal government or the State may assess the impact of ammonia in 
a particular area and determine whether the presumption of 
insignificance is appropriate or whether ammonia is in fact a 
significant contributor to the PM2.5 problem in the area.
4. Policy for VOC
    [Section II.E.2 of November 1, 2005 proposed rule (70 FR 65999); 
sec. 51.1002 in draft and final regulatory text.]
a. Background
    The VOC policy in this rule addresses volatile and semivolatile 
organic compounds, generally up to 24 carbon atoms. High molecular 
weight organic compounds (typically 25 carbon atoms or more) are 
emitted directly as primary organic particles and exist primarily in 
the condensed phase at ambient temperatures. Accordingly, high 
molecular weight organic compounds are to be regulated as primary 
PM2.5 emissions for the purposes of the PM2.5 
implementation program.
    The organic component of ambient particles is a complex mixture of 
hundreds or even thousands of organic compounds. These organic 
compounds are either emitted directly from sources (i.e. primary 
organic aerosol) or can be formed by reactions in the ambient air (i.e. 
secondary organic aerosol, or SOA). Volatile organic compounds are key 
precursors in the formation processes for both SOA and ozone. The 
relative importance of organic compounds in the formation of secondary 
organic particles varies from area to area, depending upon local 
emissions sources, atmospheric chemistry, and season of the year.
    The lightest organic molecules (i.e., molecules with six or fewer 
carbon atoms) occur in the atmosphere mainly as vapors and typically do 
not directly

[[Page 20593]]

form organic particles at ambient temperatures due to the high vapor 
pressure of their products. However, they participate in atmospheric 
chemistry processes resulting in the formation of ozone and certain 
free radical compounds (such as the hydroxyl radical [OH]) which in 
turn participate in oxidation reactions to form secondary organic 
aerosols, sulfates, and nitrates. These VOCs include all alkanes with 
up to six carbon atoms (from methane to hexane isomers), all alkenes 
with up to six carbon atoms (from ethene to hexene isomers), benzene 
and many low-molecular weight carbonyls, chlorinated compounds, and 
oxygenated solvents.
    Intermediate weight organic molecules (i.e., compounds with 7 to 24 
carbon atoms) often exhibit a range of volatilities and can exist in 
both the gas and aerosol phase at ambient conditions. For this reason 
they are also referred to as semivolatile compounds. Semivolatile 
compounds react in the atmosphere to form secondary organic aerosols. 
These chemical reactions are accelerated in warmer temperatures, and 
studies show that SOA typically comprises a higher percentage of 
carbonaceous PM in the summer as opposed to the winter. The production 
of SOA from the atmospheric oxidation of a specific VOC depends on four 
factors: Its atmospheric abundance, its chemical reactivity, the 
availability of oxidants (O3, OH, HNO3), and the 
volatility of its products. In addition, recent work suggests that the 
presence of acidic aerosols may lead to an increased rate of SOA 
formation. Aromatic compounds such as toluene, xylene, and trimethyl 
benzene are considered to be the most significant anthropogenic SOA 
precursors and have been estimated to be responsible for 50 to 70 
percent of total SOA in some airsheds. Man-made sources of aromatics 
gases include mobile sources, petrochemical manufacturing and solvents. 
Some of the biogenic hydrocarbons emitted by trees are also considered 
to be important precursors of secondary organic particulate matter. 
Terpenes (and b-pinene, limonene, carene, etc.) and the sesquiterpenes 
are expected to be major contributors to SOA in areas with significant 
vegetation cover, but isoprene is not. Terpenes are very prevalent in 
areas with pine forests, especially in the southeastern U.S. The rest 
of the anthropogenic hydrocarbons (higher alkanes, paraffins, etc.) 
have been estimated to contribute 5-20 percent to the SOA concentration 
depending on the area.
    The contribution of the primary and secondary components of organic 
aerosol to the measured organic aerosol concentrations remains a 
complex issue. Most of the research performed to date has been done in 
southern California, and more recently in central California, while 
fewer studies have been completed on other parts of North America. Many 
studies suggest that the primary and secondary contributions to total 
organic aerosol concentrations are highly variable, even on short time 
scales. Studies of pollution episodes indicate that the contribution of 
SOA to the organic particulate matter can vary from 20 percent to 80 
percent during the same day.
    Despite significant advances in understanding the origins and 
properties of SOA, it remains probably the least understood component 
of PM2.5. The reactions forming secondary organics are 
complex, and the number of intermediate and final compounds formed is 
voluminous. Some of the best efforts to unravel the chemical 
composition of ambient organic aerosol matter have been able to 
quantify the concentrations of hundreds of organic compounds 
representing only 10-20 percent of the total organic aerosol mass. For 
this reason, SOA continues to be a significant topic of research and 
investigation.
    Current scientific and technical information clearly shows that 
carbonaceous material is a significant fraction of total 
PM2.5 mass in most areas, that certain VOC emissions are 
precursors to the formation of secondary organic aerosol, and that a 
considerable fraction of the total carbonaceous material is likely from 
local as opposed to regional sources. However, while significant 
progress has been made in understanding the role of gaseous organic 
material in the formation of organic PM, this relationship remains 
complex. We recognize that further research and technical tools are 
needed to better characterize emissions inventories for specific VOC 
compounds, and to determine the extent of the contribution of specific 
VOC compounds to organic PM mass.
    In light of these factors, the proposed rule did not require States 
to address VOCs as PM2.5 attainment plan precursors and 
evaluate them for control measures, unless the State or EPA makes a 
finding that VOCs significantly contribute to a PM2.5 
nonattainment problem in the State or to other downwind air quality 
concerns. Many PM2.5 nonattainment areas are also 
nonattainment areas for the 8-hour ozone standard; control measures for 
VOCs will be implemented in some of these areas, potentially providing 
a co-benefit for PM2.5 concentrations.
b. Final Rule
    The final rule maintains the same policy as proposed.\12\ States 
are not required to address VOC in PM2.5 implementation 
plans and evaluate control measures for such pollutants unless the 
State or EPA makes a technical demonstration that emissions of VOCs 
from sources in the State significantly contribute to PM2.5 
concentrations in a given nonattainment area. Technical demonstrations 
are discussed in section II.A.8 below. If a State chooses to make a 
technical demonstration, it should be developed in advance of the 
attainment demonstration.
---------------------------------------------------------------------------

    \12\ The policy is the same as proposed, with the clarification 
regarding downwind areas discussed above (Section A.2.b).
---------------------------------------------------------------------------

c. Comments and Responses
    Comment: One commenter stated that our understanding of the 
complexities of PM2.5 formation from VOCs is limited, that 
speciated PM data are not available in all areas, and that VOC 
reductions will not reduce PM2.5 in many areas.
    Response: The EPA acknowledges the uncertainties regarding the role 
of VOC in secondary organic aerosol formation. For this reason the 
final rule does not presumptively include VOC as a regulated pollutant 
for PM planning. However, if available data demonstrates that control 
of VOC would reduce PM2.5 concentrations in an area, the 
State or EPA may include VOC as an attainment plan precursor.
    Comment: One commenter stated that the rationale that VOC should 
not be considered a PM2.5 attainment plan precursor because 
most PM areas are also ozone areas is not appropriate because many 
ozone areas will attain soon and VOC reductions will still be needed 
for PM.
    Response: The primary rationale for not including VOC as a 
PM2.5 attainment plan precursor in every nonattainment area 
is the uncertainty regarding the contribution of anthropogenic VOCs to 
the formation of the organic carbon portion of fine particles. In 
certain areas, EPA expects that VOC control measures will have some co-
benefits in the reduction of fine particulates. However, this reason 
should not be considered the principal reason for the policy in the 
final rule that VOCs presumptively should not be considered 
PM2.5 attainment plan precursors. If a State or EPA 
determines that VOCs do contribute significantly to PM2.5 
concentrations in an area, the State will be required to evaluate 
control measures for VOC as a PM2.5 attainment plan

[[Page 20594]]

precursor for that area. This approach will provide for regulation of 
VOCs in locations where it is most appropriate.
    Comment: One commenter suggested that EPA wait for the results of 
the pending agricultural emissions study before requiring control of 
VOCs in agricultural areas.
    Response: The $15 million national CAFO consent agreement study 
coordinated by Purdue University will greatly improve ammonia and VOC 
emissions inventories and our understanding of the impacts of 
agricultural emissions on particle formation. The EPA recognizes that 
the agricultural emissions study is expected to provide data for future 
planning purposes, and we expect that some of the results of the st