6560-50-P

ENVIRONMENTAL PROTECTION AGENCY

40 CFR Parts 51 and 52

[EPA-HQ-OAR-2003-0062; FRL-7969-1]

RIN 2060-AK74

CLEAN AIR FINE PARTICLE IMPLEMENTATION RULE

AGENCY:	Environmental Protection Agency (EPA).

ACTION:	Final rule.

SUMMARY:	This final action provides rules and guidance on the minimum
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.  The health
effects associated with exposure to PM2.5 are serious, including
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.  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.   	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 became effective on April 5, 2005.
By April 5, 2008, each State having a nonattainment area must submit to
EPA an attainment demonstration and associated air quality modeling,
adopted State regulations to reduce emissions of PM2.5 and its
precursors, and other supporting information demonstratingensuring that
the area will attain the standards as expeditiously as practicable.
Section I of the , but no later than 2015.  This rule and preamble
provides background information on this rulemaking.  Section II
describes the various core elements of the PM2.5 describe the
requirements that States and Tribes must meet in their implementation
program, based primarily on the subpart 1 requirements of section 172 of
the CAA.  Important topics discussed in section II include policiesplans
for addressing PM2.5 precursors, attainment dates, attainment
demonstrations and modeling, local emission reduction measures
[reasonably available control technology (RACT) and reasonably available
control measures (RACM)], and reasonable further progress (RFP).
Section III addresses the various statutory requirements and executive
orders applicable to this rule.  The final section contains the final
regulatory text for implementation of the PM2.5 NAAQS, in the form of
subpart Y amending 40 CFR part 51.  Final revisions to the new source
review program to address the fine particle standards will be set forth
in a separate rulemaking.  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 [INSERT DATE 60 DAYS FROM DATE OF
SIGNATURE].

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   HYPERLINK
"http://www.regulations.gov"  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 B1023334, 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<PHONE_NUMBER>, and the
telephone number for the Office of Air and Radiation Docket and
Information Center is<PHONE_NUMBER>. A variety of information and
materials related to the fine particle NAAQS and implementation program
are also available on EPA’s web site:    HYPERLINK
"https://www.epa.gov/pmdesignations"  https://www.epa.gov/pmdesignations
. http://www.epa.gov/air/particles.

NOTE:  The EPA Docket Center suffered damage due to flooding during the
last week of June 2006.  The Docket Center is continuing to operate.
However, during the cleanup, there will be temporary changes to Docket
Center telephone numbers, addresses, and hours of operation for people
who wish to make hand deliveries or visit the Public Reading Room to
view documents.  For current information on docket operations, locations
and telephone numbers, consult EPA’s Federal Register notice at 71 FR
38147 (July 5, 2006) or the EPA website at   HYPERLINK
"http://www.epa.gov/epahome/dockets.htm"
www.epa.gov/epahome/dockets.htm .  The Docket Center’s mailing address
for U.S. mail and the procedure for submitting comments to   HYPERLINK
"http://www.regulations.gov"  www.regulations.gov  are not affected by
the flooding and will remain the same.

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:
HYPERLINK<EMAIL_ADDRESS><EMAIL_ADDRESS>; or Ms.
Julie McClintock, 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-5339 or by e-mail at:
HYPERLINK<EMAIL_ADDRESS><EMAIL_ADDRESS>.

SUPPLEMENTARY INFORMATION:

 General Information

Does this Action Apply to Me?

[ADD REGULATED/AFFECTED ENTITIES DISCUSSION]

	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 WWW.internet.  Following
signature by the EPA Administrator, a copy of this final rule will be
posted in the regulations and standards section of our NSR home page
located at [insert location].http://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.	Are there any additional requirements related to
enforcementEnforcement and compliance?

	P.	What requirements should apply to emergencyEmergency episodes?

	Q.	What ambientAmbient monitoring requirements will apply under the
PM2.5 NAAQS?

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.	Petitions for Judicial Review tc \l2 "L.  Petitions for Judicial
Review

L.	Determination Under Section 307(d)

M.	Congressional Review Act

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 particulate matter (PM)
with a nominal aerodynamic diameter of 2.5 micrometers or less (a
micrometer is one-millionth of a meter, and 2.5 micrometers is less than
one-seventh the average width of a human hair) are considered to be
(fine particles,( and are also known as PM2.5. (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 health effects associated with exposure to PM2.5 are significant.
Epidemiological studies have shown a significant correlation between
elevated PM2.5 levels and premature mortality.  Other important 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), lung disease, decreased lung function, asthma attacks,
and certain cardiovascular problems.  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 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).  The annual standard is a level of 15 micrograms
per cubic meter, based on the 3-year average of annual mean PM2.5
concentrations.  The 24-hour standard is a level of 65 micrograms per
cubic meter, based on the 3-year average of the 98th percentile of
24-hour concentrations.  The EPA established the standards based on
evidence and numerous health studies demonstrating that serious health
effects are associated with exposures to elevated levels of PM2.5.
Estimates show that attainment of the PM2.5 standards would be likely to
result in tens of thousands fewer premature deaths each year, tens of
thousands fewer hospital admissions each year, and hundreds of thousands
fewer doctor visits, absences from work and school, and respiratory
illnesses in children annually.  The research on which EPA based the
1997 standards did not identify a specific threshold concentration below
which individuals have no PM-related health effects, meaning that
emissions reductions resulting in reduced concentrations below the level
of the standards may continue to provide additional health benefits to
the local population.

At the time we established the primary standards in 1997, we also
established welfare-based (secondary) standards identical to 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 assessment that resulted in the establishment 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 website at:  http://www.epa.gov/air/urbanair/pm/index.html.
Additional information on EPA(s scientific assessment documents
supporting the 1997 standards is available at:
http://www.epa.gov/ttn/oarpg (see headings for (Staff Papers( and
(Criteria Documents().

EPA issued final PM2.5 designations 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 PM2.5 standards.  The population of
these areas is significant - about 90 million, or more than 30% of the
U.S. population.  Most areas violate only 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 in April 2008, three
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 five years of designation (i.e.
attainment date of April 2010 based on air quality data for 2007-2009),
or within up to ten years of designation (i.e. to 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.  EPA issued the Clean Air Interstate Rule (CAIR) 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).  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 declining 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 will result
in:

-- $85 to $100 billion in annual health benefits, annually preventing
17,000 premature deaths, millions of lost work and school days, and tens
of thousands of non-fatal heart attacks and hospital admissions.

-- 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 reducing
emissions from several categories of nonroad engines.  The Tier 2 motor
vehicle emission standards, together with the associated requirements to
reduce sulfur in gasoline, will provide additional benefits nationally
beginning in 2004.  When the new tailpipe and sulfur standards are fully
implemented, Americans will 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 will lead to continued emissions
reductions as older vehicles in that engine class are retired and fleets
turn over.  New emission standards will begin to take effect in model
year 2007 and will 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 will 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.

EPA also finalized national rules in May 2004 to reduce significantly
PM2.5 and NOx emissions from nonroad diesel-powered equipment.  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.

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.  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 public health benefits of reducing PM2.5 are 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 ug/m3, efforts to improve annual average air
quality down to the level of the standard (15.0 ug/m3) may be expected
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 ug/m3 still may be expected 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.  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.

	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.  EPA is issuing this rule to
implement the PM2.5 NAAQS in accordance with the statutory requirements
of the Act set forth in Subpart 1 of Part D of Title 1, i.e., sections
171 – 179B of the Act.  EPA believes that the Act 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 PM 10 as the indicator
in accordance with Subpart 4 of Part D of Title 1, i.e., sections 188
– 190 of the Act.  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
PM 10, 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 nonattainment area 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 notice 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
sulfur dioxide (SO2), nitrogen oxides (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.  However, interactions among these pollutants are complex and
variable.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 level of
our understanding about the emissions inventories, the efficacy of
relevant control measures, and the overall contribution of thesefine
particle precursors to PM2.5 formation varies by location.  This
requires that we further consider in this action how States should
address these PM2.5 precursors in their PM2.5 nonattainment 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
nonattainment plan precursor” to describe only those precursors that
are required to be addressedevaluated 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
addressedevaluated for possible controls in each specific nonattainment
area.  The policy approach in the rule instead requires sulfur dioxide
to be addressedevaluated 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 addressevaluate
PM2.5 precursors for nonattainment program issues in PM2.5
implementation plans, 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 recent 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.  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 from sources 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 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 nonattainment 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
PM-10 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 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.

	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 nonattainment plan precursor, unless a
technical demonstration by the State or EPA showed that ammonia
emissions from sources in the State significantly contribute to the
PM2.5 problem 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 addressevaluate 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 nonattainment
plan precursor, meaning that the State is not required to address
ammonia in its nonattainment 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 the PM2.5 problem 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 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 given that there is sufficient uncertainty
regarding the impact of ammonia emission reductions on PM2.5
concentrations in all nonattainment areas.  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 nonattainment 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 nonattainment area 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.  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.  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 nonattainment 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 nonattainment 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 today’s 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 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
controversialcomplex 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 VOC’s as PM2.5 nonattainment plan precursors and evaluate them
for control measures, unless the State or EPA makes a finding that
VOC’s 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..  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 a PM2.5 problem in a given nonattainment
area.  Technical demonstrations are discussed in section II.A.8 below.
If a State chooses to make technical demonstration, it should be
developed in advance of the attainment demonstration.

c. Comments and Responsesresponses

	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 a nonattainment plan precursor.

	Comment:  One commenter stated that the rationale that VOC should not
be “out” considered a PM2.5 nonattainment 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 regulated
PM2.5 nonattainment 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 principle reason for the policy in the final rule that
VOCs presumptively should not be considered PM2.5 nonattainment 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 address evaluate control measures for VOC as a
regulatedPM2.5 nonattainment plan 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.  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 VOC emissions in their 2008 implementation plans, it may
include in its plan a demonstration to reverse the presumption as well
as emission reduction measures.  EPA will review each submittal on a
case-by-case basis.

5.  Policy for NOx

[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 sources of NOx are numerous and widespread.  The combustion of
fossil fuel in boilers for commercial and industrial power generation
and in mobile source engines each account for approximately 30 percent
of NOx emissions in PM2.5 nonattainment areas (based on 2001 emission
inventory information).  Nitrates are formed from the oxidation of
oxides of nitrogen into nitric acid either during the daytime (reaction
with OH) or during the night (reactions with ozone and water).  Nitric
acid continuously transfers between the gas and the condensed phases
through condensation and evaporation processes in the atmosphere.
However, unless it reacts with other species (such as ammonia, sea salt,
or dust) to form a neutralized salt, it will volatilize and not be
measured using standard PM2.5 measurement techniques.  The formation of
aerosol ammonium nitrate is favored by the availability of ammonia, low
temperatures, and high relative humidity.  Because ammonium nitrate is
semivolatile and not stable in higher temperatures, nitrate levels are
typically lower in the summer months and higher in the winter months.
The resulting ammonium nitrate is usually in the sub-micrometer particle
size range.  Reactions with sea salt and dust lead to the formation of
nitrates in coarse particles.  Nitric acid may be dissolved in ambient
aerosol particles.

	Based on a review of speciated monitoring data analyses, it is apparent
that nitrate concentrations vary significantly across the country. For
example, in some southeastern locations, annual average nitrate levels
are in the range of 6 to 8 percent of total PM2.5 mass, whereas nitrate
comprises 40 percent or more of PM2.5 mass in certain California
locations.  Nitrate formation is favored by the availability of ammonia,
low temperatures, and high relative humidity.  It is also dependent upon
the relative degree of nearby SO2 emissions because ammonia reacts
preferentially with SO2 over NOx.  NOx reductions are expected to reduce
PM2.5 concentrations in most areas.  However, it has been suggested that
in a limited number of areas, NOx control would result in increased
PM2.5 mass by disrupting the ozone cycle and leading to increased
oxidation of SO2 to form sulfate particles, which are heavier than
nitrate particles.  Because of the above factors, the proposed rule
presumed that States must evaluate and implement reasonable controls on
sources of NOx in all nonattainment areas, but allowed for the State and
EPA to develop a technical demonstration to reverse this presumption.

b. Final rule

	EPA is retaining the proposed approach in the final rule..  Under this
policy, States are required to address NOx as a PM2.5 nonattainment plan
precursor and considerevaluate  reasonable controls for NOx in PM2.5
nonattainment areaattainment plans, unless the State and EPA makes a
finding that NOx emissions from sources in the State do not
significantly contribute to the PM2.5 problem in a given nonattainment
area.  This policy is consistent with other recent EPA regulations
requiring NOx reductions which will reduce fine particle pollution, such
as the Clean Air Interstate Rule and a number of rules targeting onroad
and nonroad engine emissions.

	Technical demonstrations that would reverse the presumption should be
developed in advance of the attainment demonstration and are discussed
in section II.A.8 below.

c. Comments and Responsesresponses

	Comment:  Most commenters generally agreed with the proposed inclusion
of NOx as a presumptive PM2.5 nonattainment plan precursor.

	Response:  The EPA agrees with these commenters.

	Comment:  Some commenters requested guidance on what would constitute
an acceptable demonstration to reverse the presumption that NOx is a
PM2.5 nonattainment plan precursor.

	Response: Guidance on technical demonstrations to reverse the
presumptive inclusion of NOx in all state implementation plans is
discussed in section II.A.8 below.

	Comment:  One commenter raised concerns that the proposed policy for
NOx would allow a State to find NOx to be an insignificant contributor
to an area’s PM2.5 nonattainment problem and effectively keep the
State from controlling the area’s NOx emissions for other purposes,
such as to address interstate transport under section 110 of the CAA.
Section 110 requires SIPs to prohibit emissions within the State that
would contribute significantly to another State’s nonattainment
problem or interfere with another State’s maintenance plan.

	Response:  The identification of precursors for regulation under this
rule is for purposes of PM2.5 nonattainment and maintenance plans under
Part D of the Clean Air Act  The PM2.5 implementation rule does not
prevent a State from regulating NOx sources under any other federal or
state rule, including interstate transport rules under Section 110.

6.  Policy for SO2

[Section II.E.2 of November 1, 2005 proposed rule (70 FR 65999); sec
51.1002 in draft and final regulatory text.]

a. Background

	Sulfur dioxide is emitted mostly from the combustion of fossil fuels in
boilers operated by electric utilities and other industry.  Less than 20
percent of SO2 emissions nationwide are from other sources, mainly other
industrial processes such as oil refining and pulp and paper production.
 The formation of sulfuric acid from the oxidation of SO2 is an
important process affecting most areas in North America.  There are
three different pathways for this transformation.

	First, gaseous SO2 can be oxidized by the hydroxyl radical (OH) to
create sulfuric acid.  This gaseous SO2 oxidation reaction occurs slowly
and only in the daytime.  Second, SO2 can dissolve in cloud water (or
fog or rain water), and there it can be oxidized to sulfuric acid by a
variety of oxidants, or through catalysis by transition metals such as
manganese or iron.  If ammonia is present and taken up by the water
droplet, then ammonium sulfate will form as a precipitate in the water
droplet.  After the cloud changes and the droplet evaporates, the
sulfuric acid or ammonium sulfate remains in the atmosphere as a
particle.  This aqueous phase production process involving oxidants can
be very fast; in some cases all the available SO2 can be oxidized in
less than an hour.  Third, SO2 can be oxidized in reactions in the
particle-bound water in the aerosol particles themselves.  This process
takes place continuously, but only produces appreciable sulfate in
alkaline (dust, sea salt) coarse particles.  Oxidation of SO2 has also
been observed on the surfaces of black carbon and metal oxide particles.
 During the last 20 years, much progress has been made in understanding
the first two major pathways, but some important questions still remain
about the smaller third pathway.  Models indicate that more than half of
the sulfuric acid in the eastern United States and in the overall
atmosphere is produced in clouds.

	 The sulfuric acid formed from the above pathways reacts readily with
ammonia to form ammonium sulfate, (NH4)2SO4.  If there is not enough
ammonia present to fully neutralize the produced sulfuric acid (one
molecule of sulfuric acid requires two molecules of ammonia), part of it
exists as ammonium bisulfate, NH4HSO4 (one molecule of sulfuric acid and
one molecule of ammonia) and the particles are more acidic than ammonium
sulfate.  In certain situations (in the absence of sufficient ammonia
for neutralization), sulfate can exist in particles as sulfuric acid,
H2SO4.  Sulfuric acid often exists in the plumes of stacks where SO2,
SO3, and water vapor are in much higher concentrations than in the
ambient atmosphere, but these concentrations become quite small as the
plume is cooled and diluted by mixing.

	Because sulfate is a significant contributor (e.g. ranging from 9
percent to 40 percent) to PM2.5 concentrations in nonattainment areas
and to other air quality problems in all regions of the country, EPA
proposed that States would be required to address sulfur dioxide as a
PM2.5 nonattainment plan precursor in all areas.

b. Final rule

	The final rule includes the same policy for sulfur dioxide as in the
proposal.  States are required to address sulfur dioxide as a PM2.5
nonattainment plan precursor and evaluate SO2 for possible control
measures in all areas.  Sulfate is an important precursor to PM2.5
formation in all areas, and has a strong regional impact on PM2.5
concentrations.  This policy is consistent with past EPA regulations,
such as the Clean Air Interstate Rule, the Clean Air Visibility Rule,
the Acid Rain rules, and the Regional Haze rule, that require SO2
reductions to address fine particle pollution and related air quality
problems.

	Under the transportation conformity program, sulfur dioxide is not
required to be addressed in transportation conformity determinations
before a SIP is submitted unless either the state air agency or EPA
regional office makes a finding that on-road emissions of sulfur dioxide
are significant contributors to the area's PM2.5 problem.  Sulfur
dioxide would be addressed after a PM2.5 SIP is submitted if the area's
SIP contains an adequate or approved motor vehicle emissions budget for
sulfur dioxide.  EPA based this decision on the de minimis level of
sulfur dioxide emissions from on-road vehicles currently, and took into
consideration the fact that sulfur dioxide emissions from on-road
sources will decline in the future due to the implementation of
requirements for low sulfur gasoline (which began in 2004) and for low
sulfur diesel fuel (beginning in 2006).  For more information, see the
May 6, 2005 transportation conformity rule on PM2.5 precursors at 70 FR
24283.

c. Comments and Responsesresponses

	Comment:  Most commenters agreed with the proposed policy for SO2.  One
commenter stated, “…requiring states to address sulfur dioxide in
nonattainment planning in all areas is consistent with the science of
PM2.5 formation and essential to effective implementation of the PM2.5
NAAQS.”  Another commenter concluded that EPA’s proposal “…is
justified based on the fact that SO2 has been found to be a significant
contributor to PM2.5 nonattainment in all areas.”

	Response:  The EPA agrees with these comments.

	Comment:  Some commenters believe States should be able to make a
demonstration that SO2 not be addressed as a nonattainment plan
precursor.  The commenters claim that the urban increment of sulfate is
generally small, and SO2 control will not matter in many areas.
Commenters also note that a large percentage of the SO2 emission
inventory is being reduced and will be reduced further through existing
programs, and that if attainment can be demonstrated without additional
SO2 controls, a State should be allowed to make that demonstration in
its SIP.  One commenter stated that whether SO2 emissions from a given
source located in a nonattainment area in fact contribute significantly
to ambient concentrations of sulfate and PM2.5 in that nonattainment
area likely will depend on a range of factors, including source type,
stack height, location, and meteorology.  The commenter asserted that
sulfate forms over significant geographic distances from the source of
the SO2 emissions and may not form significant concentrations of PM2.5
in the local nonattainment area.

	Response:  As in the proposal, the final rule requires SO2 to be
considered a PM2.5 nonattainment plan precursor in all cases.  Sulfate
is a significant fraction of PM2.5 mass in all nonattainment areas
currently, and although large SO2 reductions are projected from electric
generating units with the implementation of the CAIR program, sulfate is
still projected to be a key contributor to PM2.5 concentrations in the
future.  SO2 emissions also lead to sulfate formation on both regional
and local scales.  EPA agrees that the extent of the contribution from a
particular source in a nonattainment area to PM2.5 concentrations in the
area will depend on a number of factors, and that at times the reaction
of SO2 emissions in the atmosphere to form sulfate particles may occur
less rapidly and extend over a significant distance.  However, at other
times the conversion of SO2 to sulfate can occur rapidly and local
impacts from a particular source can be more significant.  States are
required to develop plans to attain as expeditiously as practicable
through the identification of technically and economically feasible
control measures from the full range of source categories contributing
to PM2.5 nonattainment areas.  In developing these plans, each State
will need to consider whether controls on local SO2 sources would be
cost-effective and would be needed to attain expeditiously.

7. Policy for direct PM

 Section II.E.2 of November 1, 2005 proposed rule (70 FR 65999); sec
51.1002 in draft and final regulatory text.]

a. Background

	This section addresses inorganic and organic forms of directly emitted
PM.  Although these direct emissions are by definition not precursors to
PM2.5, this section is included to provide information on the full range
of components that commonly make up fine particulate matter.

	The main anthropogenic sources of inorganic (or crustal) particles are:
 entrainment by vehicular traffic on unpaved or paved roads; mechanical
disturbance of soil by highway, commercial, and residential
construction; and agricultural field operations (tilling, planting and
harvesting).  Industrial processes such as quarries, minerals
processing, and agricultural crop processing can also emit crustal
materials.  While much of these emissions are coarse PM, the size
distribution can have a tail of particles smaller than PM2.5.

	In general, coarse PM is most important close to the source, and not
generally a significant contributor to regional scale PM problems.  Even
so, during certain high wind events, fine crustal PM has been shown to
be transported over very long distances.

	Emission estimates of mechanically suspended crustal PM from sources
within the US are often quite high.  However, this PM is often released
very close to the ground, and with the exception of windblown dust
events, thermal or turbulent forces sufficient to lift and transport
these particles very far from their source are not usually present.
Thus, crustal material is only a minor part of PM2.5 annual average
concentrations.

 	Primary carbonaceous particles are largely the result of incomplete
combustion of fossil or biomass fuels.  This incomplete combustion
usually results in emissions of both black carbon and organic carbon
particles.  High molecular weight organic molecules (i.e., molecules
with 25 or more carbon atoms) are either emitted as solid or liquid
particles, or as gases that rapidly condense into particle form.  These
heavy organic molecules sometimes are referred to as volatile organic
compounds, but because their characteristics are most like direct PM
emissions, they will be considered to be primary emissions for the
purposes of this regulation.  Primary organic carbon also can be formed
by condensation of semi-volatile compounds on the surface of other
particles.

 	The main combustion sources emitting carbonaceous PM2.5 are certain
industrial processes, managed burning, wildland fires, open burning of
waste, residential wood combustion, coal and oil-burning boilers
(utility, commercial and industrial), and mobile sources (both onroad
and nonroad).  Certain organic particles also come from natural sources
such as decomposition or crushing of plant detritus.  Most combustion
processes emit more organic particles than black carbon particles.  A
notable exception to this is diesel engines, which typically emit more
black carbon particles than organic carbon. Because photochemistry is
typically reduced in the cooler winter months for much of the country,
studies indicate that the carbon fraction of PM mass in the winter
months is likely dominated by direct PM emissions as opposed to
secondarily formed organic aerosol.

	Particles from the earth’s crust may contain a combination of
metallic oxides and biogenic organic matter.  The combustion of surface
debris will likely entrain some soil.  Additionally, emissions from many
processes and from the combustion of fossil fuels contain elements that
are chemically similar to soil.  Thus, a portion of the emissions from
combustion activities may be classified as crustal in a compositional
analysis of ambient PM2.5.

The proposed rule required that States address the direct emissions of
particulate matter in their PM2.5 nonattainment plans.  During the
comment period, EPA received several comments regarding the definition
of what should be regulated as “direct PM2.5.”

b. Final rule

	This rule defines direct PM2.5 emissions as “air pollutant emissions
of direct fine particulate matter, including organic carbon, elemental
carbon, direct sulfate, direct nitrate, and miscellaneous inorganic
material (i.e crustal material).”   Development of nonattainment plans
will include direct PM2.5 emissions and specific PM2.5 nonattainment
plan precursors.

c. Comments and Responsesresponses

	Comment:  A few commenters noted that section40 CFR 51.1000 of the
proposed rule includes definitions for both “direct PM2.5 emissions”
and for “PM2.5 direct emissions.”  They recommend including just one
definition in the final rule.

	Response:  EPA acknowledges this oversight and has included in the
final rule a single definition for “direct PM2.5 emissions.”  It
reads:  “Direct PM2.5 emissions means solid particles emitted directly
from an air emissions source or activity, or gaseous emissions or liquid
droplets from an air emissions source or activity which condense to form
particulate matter at ambient temperatures.  Direct PM2.5 emissions
include elemental carbon, directly emitted organic carbon, directly
emitted sulfate, directly emitted nitrate, and other inorganic particles
(including but not limited to crustal material, metals, and sea
salt).”

8.  Optional technical demonstrations for NOx, VOC, and 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

	The proposed rule required States to evaluate and consider control
strategies for sources of SO2 and direct PM2.5 emissions in all
nonattainment areas.  For the precursors NOx, VOC, and ammonia, the
proposed rule included presumptive policies that could be reversed with
an acceptable technical demonstration by the State or EPA.  (The policy
in the proposal presumptively required that NOx emissions must be
addressed in all areas, and that VOC and ammonia emissions do not need
to be addressed in all areas.)  A number of commenters requested
additional guidance on the criteria for an acceptable technical
demonstration.

b. Final rule

	The final rule retains provisions for the State or EPA to conduct a
technical demonstration to reverse the presumptive inclusion of NOx or
to reverse the presumptive exclusions of ammonia and VOC as PM2.5
nonattainment plan precursors.  Demonstrations to reverse the
presumptions for ammonia, VOC, or NOx are to be based on the weight of
evidence of available information, and any demonstration by the State
must be approved by EPA.  The State must demonstrate that based on the
sum of available technical and scientific information, it would be
appropriate for a nonattainment area to reverse the presumptive approach
for a particular precursor.  The demonstration should include
information from multiple sources, including results of speciation data
analyses, air quality modeling studies, chemical tracer studies,
emission inventories, or special intensive measurement studies to
evaluate specific atmospheric chemistry in an area.

	Because of the variation among nonattainment areas in terms of such
factors as local emissions sources, growth patterns, topography, and
severity of the nonattainment problem, EPA believes that it would not be
appropriate to define a prescriptive set of analyses that must be
included in all PM2.5 precursor technical demonstrations.  The key
criterion is that any technical demonstration must fairly represent
available information.

	In developing the implementation plan for a nonattainment area, the
State should use all relevant information available (from EPA, the
State, or other sources) to determine the scientifically most
appropriate approach to regulating NOx, ammonia, and VOC emissions in
the area.  As required under any State rulemaking process, the State
must consider and provide a response in the record to any information or
evidence brought forward by commenters during the SIP planning,
development and review process which indicates that the presumption for
a precursor should be reversed.  In its review of the forthcoming State
implementation plan submittal, EPA will review the State’s proposed
precursor policies in light of all currently available information.  If
information brought forward by commenters or the State in the SIP
development process shows that the presumption in this rule for ammonia,
VOC or NOx is not technically justified for a particular nonattainment
area, the State must conduct a technical demonstration to reverse the
presumption.  In the case of ammonia or VOC, the State then would
evaluate control measures and implement those measures that are
technically and economically feasible and that will contribute to
expeditious attainment of the standards.

	In the section below we suggest examples of the types of analyses that
would be appropriate to use in developing such a demonstration.  States
are encouraged to consult with EPA in formulating appropriate technical
demonstrations.

i. Emission inventory information: An analysis might show that a
precursor composes a significant fraction of the emissions inventory in
an area and therefore requires greater consideration.

Example: Several stationary sources emitting particular VOCs known to
contribute to SOA formation make up a significant portion of the
area’s VOC inventory.  This analysis may be useful in conjunction with
other analyses included in a weight of evidence demonstration.  ,

ii. Speciation data information: Analysis of data from speciation
networks might lead a State to determine the relative importance of a
precursor to seasonal or yearly average PM concentrations.  Individual
precursors require different approaches.  Collection of new data could
be used to understand the impacts of precursors in an area.

Example: Nitrate ion is a large portion of winter average PM2.5 mass.
Nitrate ion is a major portion of PM2.5 mass on the 10 highest PM2.5
days in winter in the past 3 years.  The days with the highest mass
concentrations might be indicative of inversion conditions and/or local
impacts, rather than large-scale transport processes.  For these
reasons, nitrate should be addressed in the PM2.5 nonattainment plan.

Example: Ammonium ion data combined with total calculated nitrate data
indicates that reductions in ammonia would reduce PM concentrations
without a sharp related increase in particle acidity.  PM speciation
data shows that PM in the area is generally within 10% of calculated
neutralization.  In places for which the needed atmospheric data are
available to determine whether increased acidity is an issue, analysis
showing that increased acidity of particles and precipitation would
likely result from ammonia controls would support the presumption
against ammonia regulation.  Analysis showing that ammonia reductions
would be unlikely to increase the acidity of particles and
precipitation, and that potential reductions in ammonia would
significantly reduce PM2.5 levels, would support a technical
demonstration to reverse the presumption.

iii. Modeling information: Results of atmospheric modeling may help a
State characterize the impacts of potential precursor emission
reductions on PM2.5 concentrations in an area.

Example: Modeling of SO2, NOx, and VOC emission reductions result in
lower sulfate and nitrate levels but not lower secondary organic aerosol
levels.  This likely indicates that VOC reductions are not as vital as
reductions of the other precursors.

Example: Modeled reductions of NOx show a potential increase in sulfate
formation through disruption of the ozone cycle.  SO2 reductions may be
a better choice than NOx reductions.

Example:  Modeled ammonia reductions show a projected reduction in PM2.5
concentrations in selected areas.  Although dependant on good quality
inventory data, this type of an analysis would indicate that the area is
ammonia-limited and that ammonia reductions may be beneficial.

Example:  Modeling shows that reductions in SO2 in the absence of NOx
reductions in an area will not result in a significant PM2.5 reduction
because more nitrate particles form when less SO2 is available for
particle formation.  However, PM2.5 reductions are significant when both
SO2 and NOx are reduced concurrently.  This analysis would indicate that
NOx reductions should be included in the PM2.5 nonattainment plan in the
area.

iv. Monitoring, data analysis, or other special studies:  Could include
monitoring of gases and compounds not typically monitored under the
PM2.5 speciation network, receptor modeling analysis, or special
monitoring studies.

Example:  Data from specialized monitoring studies can provide insights
about concentrations of ammonia gas and nitric acid in an area and
whether the area is ammonia-limited or not.  Ammonia reductions in
ammonia-limited areas typically yield reductions in PM2.5
concentrations.  Specialized monitoring and laboratory studies can also
assess the relative concentrations of organic compounds and provide
insights into the contributions of different anthropogenic and biogenic
VOCs to secondary organic aerosol formation.

Example:  Receptor modeling and statistical analysis PM2.5 speciation
monitoring data can indicate relative contributions to PM2.5 mass from
sources with different chemical “fingerprints.”

Example:  Additional analysis of organic compounds on filters collected
through speciation monitoring may reveal insights about the relative
degree of carbonaceous material considered to be from fossil fuel
combustion as opposed to combustion of “modern” material (such as
wood or biomass).

 c. Comments and Responsesresponses

	Comment: A number of commenters requested that the final rule include
guidance on acceptable technical demonstrations.

	Response: The above section includes examples designed to help States
formulate appropriate demonstrations.  Prescribing specific technical
indicators to be used in all areas would ignore the scientific
uncertainty inherent in the relationships between precursor emissions
and the responses of atmospheric concentrations of PM2.5.  Therefore,
States are encouraged to review available information and consult with
EPA in formulating technical demonstrations appropriate to a particular
area.

  SEQ CHAPTER \h \r 1 B.	  No classification system for PM2.5
nonattainment areas.  tc "B.	Classification options under consideration
for PM2.5 nonattainment areas. " \l 2

1.  No classification system or a two-tiered (moderate/serious) system.

a. Background.

	Section 172 of subpart 1 contains the general requirements for SIPs for
all nonattainment areas.  Section 172(a)(1) states that on or after the
date of designation, the Administrator may classify an area for the
purpose of applying an attainment date or for some other purpose.  Thus,
a classification system is allowed under section 172 of the CAA, but is
not required for the purposes of implementing a national ambient air
quality standard.  The CAA also states that EPA may consider certain
factors in making a decision concerning classification for areas, such
as the severity of nonattainment in such areas, and the availability and
feasibility of the pollution control measures that may be needed to
achieve attainment.	In the proposed rule, EPA provided  two
implementation approaches for classifying PM2.5 nonattainment areas.
Under the first approach, there would be no classification system.
Under the second approach, a two-tiered classification system would
apply, with areas classified as either “moderate” or “serious”
based on specific criteria.

	For example, the two classification tiers could be based on the
severity of nonattainment (e.g., serious areas would be those with a
design value above a specific threshold), or on the attainment date for
the area (e.g., serious areas would be those with attainment dates after
April 2010).   However, any moderate area that needs an attainment date
longer than 5 years would be reclassified as serious.  This would ensure
that areas with a more persistent PM2.5 problem are subject to more
stringent requirements, even if they are not one of the areas with the
highest current design values.  For such areas, the State would be
required to request reclassification for an area and ensure that the
2008 attainment SIP submission for the area includes all measures needed
to meet the serious area requirements. Under the two tiered
classification approach, we proposed that serious PM2.5 nonattainment
areas would be required to meet the more stringent requirements than
moderate areas that would be defined in this rulemaking action (e.g.,
lower thresholds for RACT, fixed percentage reduction for RFP, etc.).
For serious areas, the attainment date would be as expeditious as
practicable, but no later than 10 years after designation, depending on
the year in which the area would be projected to attain considering
existing control requirements and the effect of RACM, RACT and RFP.

b. Final rule.

	 The EPA believes that in the case of PM2.5, the no-classification
approach is the most appropriate approach.  An advantage of this
approach is that it provides a relatively simple implementation
structure for State implementation of the PM2.5 standards, and avoids
the need to define a classification system and determine classifications
for each area.  Without classifications, this rule still requires that
that SIPs include all reasonable measures that contribute to achieving
attainment as expeditiously as practicable.  (Further detail is provided
in sections D. and F. below.)  Because of differences in the nature and
sources of the PM2.5 problem in different parts of the country, EPA did
not find it appropriate to establish a tiered classification system with
increasing control measure requirements.  The no-classifications
approach provides States with greater flexibility to determine the
control strategies that will be most effective and efficient in bringing
specific areas into attainment as expeditiously as practicable.  	In
addition, EPA believes that States requesting additional time to attain
the standard beyond the initial 5 year attainment date, provided for
under Subpart I, will need to adopt additional or more stringent
measures to meet their obligations for RACT, RACM and attainment that is
as expeditious as practicable.   We believe that this addresses the main
concerns of those commenters who contend that a two tiered
classification system should be implemented.

c. Comments and Responsesresponses.

	Comment:   The majority of the commenters who commented on this issue
stated that they agreed with EPA’s preferred no classification
approach.  These commenters generally stated that they believed that EPA
has the authority not to establish a classification system for PM2.5
nonattainment areas.  Some commenters stated that it would also be
unreasonable, at this point in the process, for EPA to implement a
classification scheme for the PM2.5 standard.  Many commenters support
the no classification approach because it provides for a simple
implementation structure and/or allows greater implementation
flexibility to States, including flexibility to address specific
problems related to individual nonattainment areas in the most
cost-effective and expeditious manner, rather than through a one size
fits all approach.  Other commenters stated that they believe that a
classification system is not needed because  nonattainment areas in the
Eastern United States are likely to attain the standard within a
timeframe that is consistent with the timeframe established under
Subpart 1.

	Response: The EPA agrees with these commenters.

	Comment:   Several commenters disagreed with EPA’s preferred approach
and agreed with the two tiered classification approach featuring a
“moderate” and a “serious” area classification. These commenters
also stated that the threat of reclassification or “bump up” to a
higher classification was a powerful incentive for areas to attain as
expeditiously as practicable.  Commenters also indicated that areas
needing more time to attain the standard should be required to implement
more stringent measures or mandatory measures.

	Response:   The EPA agrees that areas with more severe nonattainment
problems will need to implement more stringent measures to attain.
However, EPA does not believe that a classification system is needed to
ensure that such measures are implemented.  The EPA believes that on
balance the no classification approach is the most appropriate
classification option for the implementation of the PM2.5 standard
because of the difference in contributing sources from area to area.

	Comment:  Several commenters stated that under EPA’s preferred
approach, each State would be required to submit an attainment
demonstration proposing an attainment date that is “as expeditious as
practicable” for each area.  They asserted that to allow States to
propose their own attainment dates would invite delay in the process of
cleaning up fine particle pollution.  These commenters further stated
that States would have no incentive to set an attainment date earlier
than the outer limit set by EPA, even if it would be practicable to
attain the NAAQS sooner.

	Response:   Section 172 of the CAA requires SIPs to demonstrate
attainment as expeditiously as practicable regardless of whether there
is a classification system, and under this rule states must justify that
their attainment date is as expeditious as practicable considering all
reasonable measures.  As noted above, EPA believes that States
requesting additional time to attain the standard beyond the initial 5
year attainment date will need to adopt additional or more stringent
measures to meet their obligations for RACT and RACM and to attain as
expeditiously as practicable.  More details on the analytical process
required for an attainment demonstration is included in section II.F.

	Comment:   Several commenters stated that the CAA requires regulation
of the PM2.5 standard under Subpart 4 of Part D.  These commenters State
that EPA takes the position that it must regulate PM2.5 under Subpart 1
of the CAA, which applies to nonattainment areas in general.  The
commenters State that section 7513, in Subpart 4 of Part D of the CAA,
contains specific provisions for classification of particulate matter
nonattainment areas, and that EPA must therefore regulate PM2.5 under
Subpart 4, which requires a moderate and serious area classification
system.  Other commenters argued that implementation of the PM2.5
standard must proceed under Subpart 1 of Part D of Title I of the CAA
and cannot be governed by Subpart 4 of Part D, which addresses the
implementation of the PM10 standard which is a different pollutant than
PM2.5.

	Response:   The EPA finds that the PM2.5 standard should be implemented
under subpart I of the CAA, which is the general provision of the CAA
related to NAAQS implementation.  Part D of Title I of the CAA sets
forth the requirements for SIPs needed to attain the national ambient
air quality standards.  Part D also includes a general provision under
Subpart I which applies to all NAAQS for which a specific subpart does
not exist.  Because the PM2.5 standards were not established until 1997,
the nonattainment plan provisions found in section 172 of subpart 1
apply.  The EPA further agrees with comments stating that subpart 4 on
its face applies only to the PM10 standard.  In general, the emphasis in
subpart 4 on reducing PM10 concentrations from certain sources of direct
PM2.5 emissions can be somewhat effective in certain PM2.5 nonattainment
areas but not in all.  Contributions to PM2.5 concentrations are
typically from a complex mix of sources of primary emissions and sources
of precursor emissions which form particles through reactions in the
atmosphere.  PM2.5 also differs from PM10 in terms of atmospheric
dispersion characteristics, chemical composition, and contribution from
regional transport.

2.  Rural transport classification  tc "2.  Rural transport
classification " \l 4 option

a. Background.

	The 8-hour ozone implementation program includes a “rural transport
classification” for subpart 1 nonattainment areas.  In the proposal
for this rule we discussed whether an area classification of this type
would be appropriate for the PM2.5 implementation program in light of
the fact that no currently designated PM2.5 nonattainment area met the
criteria similar to those that apply to rural transport areas under the
ozone implementation program.

	As addressed in the proposal, a PM2.5 nonattainment area would qualify
for the “rural transport” classification if it met criteria similar
to those specified for rural transport areas for the 1-hour ozone
standard under section 182(h).  Section 182(h) defines “rural
transport” areas as those areas that do not include, and are not
adjacent to, any part of a Metropolitan Statistical Area (MSA) or, where
one exists, a Consolidated Metropolitan Statistical Area (CMSA).
Section 182(h) further limits the category to those areas whose own
emissions do not make a significant contribution to pollutant
concentrations in those areas, or in other areas.

	As discussed in the preamble to the proposed rule, potential criteria
for a State to identify an area for a rural transport classification
under the PM2.5 program could be similar to the criteria used in the
ozone implementation program:  a State with a PM2.5 “rural
transport” area would need to 1) demonstrate that the area meets the
above criteria,  2) demonstrate using EPA approved attainment modeling
that the nonattainment problem in the area is due to the “overwhelming
transport” of emissions from outside the area, and 3) demonstrate that
sources of PM2.5 and its precursor emissions within the boundaries of
the area do not contribute significantly to PM2.5 concentrations that
are measured in the area or in other areas.

	An area which qualifies for the “rural transport” classification
would only be required to adopt local control measures sufficient to
demonstrate that the area would attain the standard by its attainment
date “but for” the overwhelming transport of emissions emanating
from upwind States.  RFP requirements under subpart 1 would still apply
to these areas.  As with other nonattainment areas, rural transport
nonattainment areas would be subject to NSR, transportation conformity,
and general conformity requirements.  In the proposal we solicited
comments on whether it would be appropriate to establish less burdensome
NSR requirements in the event that a classification for rural transport
areas is adopted in the final rule.  The EPA requested comment on
whether this type of classification option is needed at all under the
PM2.5 implementation program.

b. Final rule.

	The final rule does not include a rural transport classification.  This
type of classification was included in the CAA for purposes of
implementing the ozone standards because of the phenomenon of the
formation of high ozone levels far downwind in very rural locations,
including on high elevation mountain peaks.  In reviewing the currently
designated PM2.5 nonattainment areas, it appears that all areas but one
are within or adjacent to a metropolitan area (i.e. core-based
statistical area or consolidated statistical area), and thus would not
meet the criteria discussed above.  Although PM2.5 concentrations are
greatly affected by long-range transport of air pollution, it appears
that nonattainment areas typically are located in urban areas and
include significant local pollutant sources.

c. Comments and responses

	Comment:   Several commenters stated that they do not support the
adoption of a rural transport classification because it is not needed.
Commenters stated that given the criteria for the rural transport
classification, which greatly limits its applicability, few if any PM2.5
nonattainment areas can qualify for the option. One commenter stated
that EPA modeled the rural transport classification after the “rural
transport areas” provision contained in subpart 2 of the CAA, which
applies only to the ozone standard.  The commenter further states that
neither Subpart 1 nor 4 contain any statutory authority for such a
classification.

	Response:  The EPA believes that it has sufficient statutory authority
under the CAA to establish a rural transport classification, but we do
not believe that such a classification is needed.

	Comment:   One commenter generally supported the rural transport
concept and the proposed associated requirements, with the addition that
data analysis be included as appropriate in the required technical
demonstrations in addition to modeling.  While no PM2.5 area currently
meets the requirements for the rural transport classification option,
several commenters recommended that it be maintained for potential cases
in which the PM2.5 standards are made more stringent, or measured air
quality in areas change in such a way that areas would qualify for the
rural transport classification at a later date.

	Response: The EPA does not agree that a rural transport classification
is needed.  The EPA will re-evaluate the need for such a classification
as appropriate.

 When are PM2.5 attainment demonstrations and SIPs due and what
requirements must they address?

C.  Due dates and basic requirements for attainment demonstrations

a. Background.

	 Part D of Title I of the CAA sets forth the requirements for SIPs
needed to attain the national ambient air quality standards.  Part D
includes a general subpart 1 which applies to all NAAQS for which a
specific subpart does not exist.  The 1990 CAA Amendments do not include
any subpart for PM2.5 because the PM2.5 standards were not yet
established.  The EPA has determined that for PM2.5, the nonattainment
plan provisions found in section 172 of subpart 1 apply.

	Section 172(b) of the CAA requires that at the time the Agency
promulgates nonattainment area designations, the EPA must also establish
a schedule for States to submit SIPs meeting the applicable requirements
of section 172(c) and of section 110(a)(2) of the CAA.  Nonattainment
area designations were finalized in December 2004, and a supplemental
notice was issued in April 2005.  Consistent with section 172(b) of the
CAA, section40 CFR 51.1002 of the proposed rule requires the State to
submit its attainment demonstration and SIP revision within 3 years, or
by April 2008.

	Section 51.1006 of the proposed rule addresses the situation in which
an area is initially designated as attainment/unclassifiable but is
later designated as nonattainment based on air quality data after the
2001-2003 period.  Under such circumstances, the SIP submittal date
would be 3 years from the effective date of the redesignation, and the
attainment date would be as expeditiously as practicable but no later
than 5 years from the effective date of the redesignation.

	The section 172(c) requirements that States are to address under
section 172(c) (including RACT, RACM, RFP, contingency measures,
emission inventory requirements, and NSR) are discussed in later
sections of this notice.  Section 110(a)(2) of the CAA requires all
States to develop and maintain a solid air quality management
infrastructure, including enforceable emission limitations, an ambient
monitoring program, an enforcement program, air quality modeling, and
adequate personnel, resources, and legal authority.  Section
110(a)(2)(D) also requires State plans to prohibit emissions from within
the State which contribute significantly to nonattainment or maintenance
areas in any other State, or which interfere with programs under part C
to prevent significant deterioration of air quality or to achieve
reasonable progress toward the national visibility goal for Federal
class I areas (national parks and wilderness areas).  In order to assist
States in addressing their obligations regarding regionally transported
pollution, EPA has finalized the CAIR to reduce SO2 and nitrogen oxide
emissions from large electric generating units.

	To date, few states have submitted a SIP revision addressing the
section 110(a)(2) requirements for the purposes of implementing the
PM2.5 standards.  The EPA recognizes that this situation is due in part
to the fact that there were a series of legal challenges to the PM
standards which were not resolved until March 2002, at which time the
standards and EPA’s decision process were upheld (see section I.B. for
further discussion of past legal challenges to the standards).  To
address the States’ continuing obligation to address the requirements
of section 110(a), section40 CFR 51.1002 of the proposed rule also
required each State to address the required elements of section
110(a)(2) of the CAA in its nonattainment plan SIP revision, if it has
not already done so. On March 10, 2005, EPA entered into a consent
decree with Environmental Defense and American Lung Association
concerning EPA’s failure to find that States failed to submit SIPs to
address the section 110(a)(2) requirements.  As a part of that consent
decree, by no later than October 8, 2008, EPA is required to publish a
notice in the Federal Register related to its determinations of whether
each State has submitted SIPs for PM2.5 that meet the requirements as
stated under section 110(a)(2) of the CAA.

b. Final Rule.

	The final rule maintains the regulatory approach described above.

c. Comments and Responsesresponses.

	There were no comments on this portion of the proposal.

D.  How will the attainment date for a PM2.5 nonattainment area be
determined? Attainment dates

1. Background on statutory requirements.

	Establishing attainment dates.  Section 172(a)(2) states that an
area’s attainment date “shall be the date by which attainment can be
achieved as expeditiously as practicable, but no later than 5 years from
the date such area was designated nonattainment …, except that the
Administrator may extend the attainment date to the extent the
Administrator determines appropriate, for a period no greater than 10
years from the date of designation as nonattainment considering the
severity of nonattainment and the availability and feasibility of
pollution control measures.”

	Since PM2.5 designations have an effective date of April 2005, the
initial 5-year attainment date for PM2.5 areas would be no later than
April 2010.  For an area with an attainment date of April 2010, EPA
would determine whether it had attained the standard by evaluating air
quality data from the three previous calendar years (i.e. 2007, 2008,
and 2009).

	For any areas that are granted the full 5 year attainment date
extension under section 172, the attainment date would be no later than
April 2015.  For such areas, EPA would determine whether they have
attained the standard by evaluating air quality data from 2012, 2013,
and 2014.  Section 51.1004 of the proposed regulations addressed the
attainment date requirement.  Section 51.1004(b) provided that in their
attainment demonstrations, States would propose an attainment date
representing attainment as expeditiously as practicable based upon
implementation of existing Federal and State measures, and all new
reasonable local and intrastate measures.  The EPA would approve a
particular attainment date based on its review of the attainment
demonstration.

Determining Whether an Area Has Attained.  The EPA has the
responsibility for determining whether a nonattainment area has attained
the standard by its applicable attainment date.  Section 179(c)(1) of
the Act requires EPA to make determinations of attainment no later than
6 months following the attainment date for the area.  Under section
179(c)(2), EPA must publish a notice in the Federal Register identifying
those areas which failed to attain by the applicable attainment date.
The statute further provides that EPA may revise or supplement its
determination of attainment for the affected areas based upon more
complete information or analysis concerning the air quality for the area
as of the area(s attainment date.

Section 179(c)(1) of the Act provides that the attainment determination
for an area is to be based upon an area(s (air quality data as of the
attainment date.(  The EPA will make the determination of whether an
area(s air quality is meeting the PM2.5 NAAQS by the applicable
attainment date primarily based upon data gathered from the air quality
monitoring sites which have been entered into EPA(s Air Quality System
(AQS) database.  No special or additional SIP submittal will be required
from the State for this determination.

 μg/m3.  The 24-hour standard for PM2.5 is met when the average of 98th
percentile values for three consecutive calendar years at each
monitoring site is less than or equal to 65.5 μg/m3.

The EPA will begin processing and analyzing data related to the
attainment of PM2.5 areas immediately after the applicable attainment
date for the affected areas.  Current EPA policy, under 40 CFR part 58,
sets the deadline for submittal of air quality data into the AQS
database for no later than 90 days after the end of the calendar year.

While EPA may determine that an area(s air quality data indicates that
an area may be meeting the PM2.5 NAAQS for a specified period of time,
this does not eliminate the State(s responsibility under the Act to
adopt and implement an approvable SIP.  If EPA determines that an area
has attained the standard as of its attainment date, the area will
remain classified as nonattainment until the State has requested, and
EPA has approved, redesignation to attainment for the area.

In order for an area to be redesignated as attainment, the State must
comply with the five requirements listed under section 107(d)(3)(E) of
the Act.  This section requires that :

- EPA has determined that the area has met the PM2.5 NAAQS;

- EPA has fully approved the state’s implementation plan;

- the improvement in air quality is due to permanent and enforceable
reductions in emissions;

- EPA has fully approved a maintenance plan for the area;

- the State(s) containing the area have met all applicable requirements
under section 110 and part D.

2. Determination ofEstablishing Attainment Dates

a. Background

	The EPA proposed rule language on attainment dates that closely tracks
the statutory language.  In the preamble, EPA noted that the attainment
date that is as expeditious as practicable should reflect the projected
impact of existing national and State programs (e.g. partial
implementation of the CAIR rule, final Acid Rain Program, motor vehicle
tier II standards and heavy-duty diesel engine standards, NOx SIP call,
State legislation such as Clean Smokestacks bill in North Carolina) as
well as additional reasonable measures required for the PM2.5
nonattainment SIP.

	With respect to its authority to extend an area’s date beyond 5
years, EPA stated in the preamble that the State can submit a SIP
demonstrating that it is impracticable to attain by the 5-year
attainment date:

 “As stated previously, under section 172(a)(2)(A), EPA may grant an
area an extension of the initial attainment date for a period of one to
5 years.  States that request an extension of the attainment date under
this provision of the CAA must submit a SIP in 2008 that includes, among
other things, an attainment demonstration showing that attainment within
5 years of the designation date is impracticable.  It must also show
that the area will attain the standard by an alternative date that is as
expeditiously as practicable, but in no case later than 10 years after
the designation date for the area (i.e. by April 2015 for an area with
an effective designation date of April 2005).  An appropriate extension
in some cases may be only 1 or 2 years - a 5-year extension is not
automatic upon request.

	The attainment demonstration must provide sufficient information to
show that attainment by the initial attainment date is impracticable due
the severity of the nonattainment problem in the area, the lack of
available control measures, and any other pertinent information which
shows that additional time is required for the arearelated to attain the
standardthese statutory criteria.   States requesting an extension of
the attainment date must also demonstrate that all local control
measures that are reasonably available and technically feasible for the
area are currently being implemented to bring about expeditious
attainment of the standard by the alternative attainment date for the
area.  The State(s plan will need to project the emissions reductions
expected due to Federally enforceable national standards, State
regulations, and local measures such as RACT and RACM, and then conduct
modeling to project the level of air quality improvement in accordance
with EPA(s modeling guidance.  The EPA will not grant an extension of
the attainment date beyond the initial five years required by section
172(a)(2)(A) for an area if the State has not considered the
implementation of all RACM and RACT local control measures for the area
(see section III.I for a more detailed discussion of RACT and RACM).
The EPA also will examine whether the State has adequately considered
measures to address intrastate transport of pollution from sources
within its jurisdiction.  In attainment planning, States have the
obligation and authority to address the transport of pollution from one
area of the State to another.  Any decision made by EPA to extend the
attainment date for an area beyond its original attainment date will be
based on facts specific to the nonattainment area at issue and will only
be made after providing notice in the Federal Register and an
opportunity for the public to comment.”

b. Summary of finalFinal rule

	We are adopting the approach described above from the proposed rule.
We also wish to clarify language that was in the preamble to the
proposed rule regarding the criteria for an extension.  The preamble
stated that attainment date extensions would be based on the two
statutory extension criteria – “the severity of nonattainment, and
the availability and feasibility of pollution control measures,” - as
well as “other pertinent information which shows that additional time
is required for the area to attain the standard.”  The Clean Air Act
does not include this third clause and the regulatory text for the final
rule does not include this third clause.  The intent of this language in
the preamble to the proposal was that States could include “other
pertinent information” related to the two statutory criteria.

c. Comments and responses

	Comment: Some commenters expressed concern that EPA’s preamble
language appeared to assert a new basis for granting extensions not
provided by the statute.  They said EPA has authority to extend the
attainment date under Section 7502(a)(2) based solely on consideration
of  two enumerated factors:  the severity of nonattainment, and the
availability and feasibility of control measures.

	Response:  The EPA agrees that extensions must be based upon the two
factors in the statute, which are quite broad.  A clarification of the
preamble phrase cited by the commenter is provided above. The phrase in
question – “any other pertinent information which shows that
additional time is required for the area to attain the standard” --
refers to information that relates to the two statutory factors.

	Comment:  One commenter stated that an area should qualify for an
extension only if the area will implement stringent local controls, yet
still cannot practicably attain by the five-year deadline.  The
commenter stated that at a minimum, EPA must require states to adopt
RACM for both mobile and stationary sources before granting an
extension.  Another commenter said that given the difficulty many areas
will have in meeting the five-year deadline for attainment of the PM2.5
NAAQS (and especially in light of the fact that the deadline occurs only
2 years after states are to submit attainment SIPs), EPA should provide
maximum flexibility in allowing extensions to the full 10-year period.

	Response:  The EPA agrees that extensions should be granted only if an
area cannot practicably attain within 5 years despite application of all
reasonable measures, including RACM.  Although some measures can be
implemented within a year or two, many measures require a longer period
for installation of controls or full program implementation.  In light
of the limited time period between the SIP submittal deadline and the
5-year date, EPA believes that a significant number of areas may warrant
extensions ranging from one to 5 years, with the length of extension
depending on the factors described above.

	Comment:  One commenter advocated that EPA include in this final rule a
determination of those areas for which attainment within 5 years is
impracticable.  Another commenter advocated that EPA establish guidance
based on EPA national modeling conducted last year to establish 2015 as
constituting expeditious attainment for certain areas.

	Response: The EPA is not determining in this rulemaking the areas that
should receive extensions or should receive the maximum 10-year
attainment date, for several reasons.  First, EPA did not propose such
an approach.  Therefore, the public has not had the opportunity to
comment on the approach or on the technical information on which EPA
would make such judgments.

	Second, EPA believes that modeling being conducted by the states, with
updated inventories and finer grids, will generally provide a more
reliable basis for projecting future PM2.5 base case levels than
national modeling conducted by EPA with older information.  State
modeling of future year PM2.5 levels that has been conducted to date
indicates that some areas will start closer or farther from the standard
than EPA had projected.

	Third, the SIP process provides a forum for states to identify
reasonable controls and conduct analyses to determine the appropriate
attainment date for an area.  This process provides for input from
expert stakeholders, the general public, other states which may share
the same multi-State nonattainment area, and EPA on decisions regarding
controls and attainment dates.  At this time, EPA does not have the
benefit of this process to inform a judgment as to when areas can
practicably attain.  States are responsible for developing RACM
demonstrations; at this time, EPA lacks the information to conduct a
credible RACM demonstration for all PM2.5 nonattainment areas.

	Fourth, no State commenter advocated that EPA attempt to make these
judgments on attainment dates in advance of the State SIP process.  The
statute gives the states the lead in developing State implementation
plans.

	Comment:  Another commenter recommends that an area should receive an
attainment date extension when collectively the following conditions
have been met:

It is proven through modeling that the region is adversely effected by
transport of PM2.5 emissions from up wind sources beyond that State(s
control;

A State has submitted and committed to implementing all Federal PM2.5
emission reduction requirements in a timely manner; and,

The extension concept is approved through the State air agency or
through the MPO Interagency Consultation Process at the MPO level if
applicable.

	Response:  This commenter advocates for attainment date extensions
without any consideration of reasonable local measures.  As stated
above, EPA believes that extensions should be granted only if an area
cannot practicably attain within 5 years despite application of all
reasonable measures, including RACM.  Although some measures can be
implemented within a year or two, many measures may require a longer
period for installation of controls or full program implementation.  In
light of the limited time period between the SIP submittal deadline and
the 5-year date, EPA believes that a significant number of areas may
warrant extensions ranging from one to 5 years, with the length of
extension depending on the factors described above.

3.  Attainment dates:  1-year extensions

a.  Background.

	Subpart 1 provides for States to request two 1-year extensions of the
attainment date for a nonattainment area under limited circumstances.
Section 172(a)(2)(C) of the CAA provides that EPA initially may extend
an area(s attainment date for 1 year, provided that the State has
complied with all the requirements and commitments pertaining to the
area in the applicable implementation plan, and provided that the area
has had no more than a minimal number of (exceedances( of the relevant
standard in the preceding year.  Because the PM2.5 standards do not have
exceedance-based forms but are based on 3-year averaging periods, we
interpret the air quality test in section 40 CFR 51.1005 to mean that
the area would need to have (clean data( for the third of the 3 years
that are to be evaluated to determine attainment.   By this we mean that
for the third year, the air quality for all monitors in the area as
analyzed in accordance with Appendix N to 40 CFR Part 50 each must have
an annual average of 15.0 μg/m3 or less, and a 98th percentile of
24-hour monitoring values of 65 μg/m3 or less in order to qualify for a
1-year extension.  (Given the rounding provisions specified in 40 CFR
Part 50, Appendix N, these criteria would be satisfied if the
concentrations before final rounding are less than an annual average of
15.05 μg/m3 and a 24-hour value of 65.5 μg/m3.)

	For example, suppose an area in violation of the annual standard has an
attainment date of April 2010, and its annual average for 2007 was 15.8
and for 2008 was 15.6.  If the annual average for the area in 2009 is
14.9, then the 3-year average would be 15.4, and it would not have
attained the standard.  We interpret section 172(a)(2)(C) as allowing
the area to submit a request to EPA for a 1-year extension of its
attainment date to 2011 (provided the State has also complied with its
requirements and commitments) since the 14.9 ambient air quality value
in the third year (2009) met the test of being at or below 15.0.
Section 51.1005(a) of the proposed regulation addresses the initial
1-year attainment date extension.

	The air quality measured in 2010 in conjunction with prior data will
determine if the area attains the standard, qualifies for a second
1-year extension, or does not attain the standard.  For example, if the
area(s annual average for 2010 is 14.3, then its 3-year average for
2008-2010 would be 14.9 and it would have met the annual standard.

	If the area(s annual average for 2010 is 14.9, however, then its 3-year
average for 2008-2010 would be 15.1.  In this situation the area would
not have attained the standard, but the area would meet the air quality
test for the second of the 1-year extensions allowed under section
172(a)(2)(C), because the 2010 annual average was at or below 15.0.
Section 51.1005(b) of the proposed rule addresses the second 1-year
attainment date extension.  After obtaining a second 1-year extension,
the State would evaluate whether the air quality values in 2011, in
conjunction with 2009 and 2010 data, bring the area into attainment.

	Pursuant to section 172(a)(2)(C), States must submit additional
information to EPA to demonstrate that they have complied with
applicable requirements, commitments, and milestones in the
implementation plan.  This information is needed in order for EPA to
make a decision on whether to grant a 1-year attainment date extension.
The EPA will not be inclined to grant a 1-year attainment date extension
to an area unless the State can demonstrate that it has met important
requirements contained in the area(s implementation plan.  States must
demonstrate that: (1) control measures have been submitted in the form
of a SIP revision and substantially implemented to satisfy the
requirements of RACT and RACM for the area, (2) the area has made
emissions reductions progress that represents reasonable further
progress (RFP) toward attainment of the NAAQS, and (3) trends related to
recent air quality data for the area indicate that the area is in fact
making progress toward attainment of the standard.  Any decision made by
EPA to extend the attainment date for an area will be based on facts
specific to the nonattainment area at issue, and will only be made after
providing notice in the Federal Register and an opportunity for the
public to comment.

	If an area fails to attain the standard by the attainment date, EPA
would publish a finding to this effect in accordance with section 179 of
the CAA.  The area then would be required, within 1 year of publication
of this finding, to develop a revised SIP containing additional emission
reduction measures needed to attain the standard as expeditiously as
practicable.

b.  Final ruleRule.

	The final rule retains the proposed criteria for states to receive a
1-year attainment date extension for a nonattainment area.

c.  Comments and Responses

	Comment:  A number of commenters supported EPA(s ability to grant a
1-year attainment date extension if monitoring data indicate that the
PM2.5 levels during the most recent year were below 15.05 ug/m3.

	Response:  The EPA agrees with these comments.

	Comment:  Some commenters recommended that a 1-year extension be
provided if the trend line of the area’s emissions levels or air
quality data projects attainment in the extension year.

	Response:  The EPA believes that 1-year extensions should be based on
air quality data, which can be assessed quickly after the end of the
year.  Basing such extensions solely on emissions trends would be
impractical due to the longer turnaround time needed to evaluate
emissions changes affecting a monitor.

	Comment:  One commenter believes the current requirement is overly
stringent and inconsistent with the statute.  The commenter believes
that EPA’s proposed approach incorrectly defines the statutory
language referring to a “minimal number of exceedances” of the
standard in the previous year as “zero” exceedances.
Alternatively, the commenter suggests EPA could withdraw this provision
and provide more detailed guidance giving the Agency and states some
flexibility to demonstrate that exceedances were minimal in a given case
since nothing in the statute requires the rigid definition of minimal
that EPA proposes.

	Response:  The EPA believes the policy in the final rule is a
reasonable application of the statutory language to a standard not based
on exceedances.  The EPA does not believe it would be appropriate to
provide a 1-year extension to an area with air quality data showing it
violating the standard over the 3 years prior to the attainment year.

4.  Achieving “Clean Data” Prior to the area’s approved attainment
date

 a.  Background

	Section III.D of the preamble to the proposed rule describes the
incentives for attaining the standards prior to April 2008, when SIP
submittals are due, or prior to an area’s approved attainment date.
Areas with design values just over the level of the standard may be able
to achieve reductions in the local area or in the State so that, when
their effect is considered in combination with reductions achieved under
national programs, they may be sufficient to attain the standards before
SIPs are due in 2008.  For example, if monitoring in a nonattainment
area shows that the air quality for 2004-2006 meets the standards, then
the area may be subject to reduced regulatory requirements and be
redesignated as (attainment.(