explanation in a state's attainment plan submission.
    (1) Existing control measures. The EPA proposes that, as a starting
point, a state must include in its initial list of control measures
those measures and technologies that are being implemented or will be
implemented due to promulgated and/or adopted (i.e., ``on the books'')
regulations for sources of direct PM2.5 and PM2.5
precursors in its Moderate PM2.5 nonattainment area. The EPA
expects that the state will incorporate current or anticipated
emissions reductions from these ``existing'' control measures (such as
expected SO2 reductions from the MATS; reductions of
NOX and direct PM2.5 from engine and fuel
standards to reduce emissions from on-road and nonroad mobile sources)
into its attainment demonstration modeling for the nonattainment area,
and therefore the EPA believes it is appropriate for the state to
clearly indicate such measures in the attainment plan for the area.
    The EPA recognizes that for some sources located in a Moderate
PM2.5 nonattainment area, a state may have previously
conducted RACM and RACT analyses to address emissions for other
statutory purposes. Some of the RACM and RACT determinations could be
relatively recent, while other determinations may be 15 years old or
older. The EPA proposes that a state may not simply rely on a previous
RACM or RACT determination for a particular source or source category
when developing the attainment plan for a PM2.5 NAAQS, but
rather that the state must consider all existing and potential new
measures together as part of a comprehensive RACM and RACT analysis. In
this way, the state's new RACM and RACT analysis will represent the
most thorough, up-to-date review of control measures for its
PM2.5 nonattainment area. For example, the state would still
need to provide a RACT analysis for a stationary source that has
installed new emissions controls recently (e.g., within the last 3
years), but the state's determination may consider that recent
installation when determining whether additional control is
technologically and economically feasible.
    (2) Potential control measures. In addition to identifying existing
control measures for sources in a Moderate PM2.5
nonattainment area, a state must develop a comprehensive list of
potential control measures for sources in the area. There are a number
of resources available to assist states in identifying additional,
potential control measures and control technologies for their RACM and
RACT and additional reasonable measures determinations for their
Moderate PM2.5 nonattainment areas. First, the EPA's Office
of Air Quality Planning and Standards maintains a Menu of Control
Measures document, available online at http://www.epa.gov/air/criteria.html. This document was developed to provide information
useful in the development of local emissions reduction and NAAQS SIP
scenarios, and identifying and evaluating potential control measures.
It provides a broad, though not comprehensive, listing of potential
emissions reduction measures for direct PM2.5 and precursors
of ozone and PM2.5 from stationary, area and mobile sources.
More complete information on mobile source control measures can be
found on the EPA's Office of Transportation and Air Quality Web site at
http://www.epa.gov/otaq.
    The RACT/BACT/LAER Clearinghouse (RBLC) provides a central database
of air pollution technology information (including past RACT, BACT and
LAER decisions contained in NSR permits) to promote the sharing of
information among permitting agencies and to aid in future case-by-case
control measure determinations. The RBLC permit database contains over
5,000 determinations that can help a state identify appropriate
technologies to mitigate most air pollutant emission streams. The RBLC
includes data submitted by several U.S. territories and all 50 states
on over 200 different air pollutants and 1,000 industrial processes.
The RBLC can be found at: http://cfpub.epa.gov/rblc/.
    Additionally, the EPA maintains a Web site with links to other
online sources of information on control measures for states to
consider.\90\ Again, the EPA recognizes that some control technology
guidance for certain source categories has not been updated for many
years, and, for this reason, the agency expects states to identify and
consider new and updated information in their RACM and RACT
determinations as it becomes available.
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    \90\ Links are provided to a number of national, state and local
air quality agency sites from the EPA's PM2.5 Web site:
http://www.epa.gov/pm/measures.html.
---------------------------------------------------------------------------

    (3) RACM for managing emissions from wildfire and prescribed fire.
Wildfire emissions account for a large portion of direct
PM2.5 emissions nationally and can significantly contribute
to periodic high PM2.5 levels.\91\ Besides their effect on
air quality, wildfires pose a direct threat to public safety--a threat
that can be mitigated through management of wildland vegetation.
Attempts to suppress wildfires have resulted in unintended
consequences, including increased risks to both humans and
ecosystems.\92\ The use of wildland prescribed fire can influence the
occurrence, behavior, and effects of catastrophic wildfires which may
help manage the contribution of wildfires to background
PM2.5 levels and periodic peak PM2.5 events.
Additionally prescribed fires can have benefits to those plant and
animal species that depend upon natural fires for propagation, habitat
restoration, and reproduction, as well as myriad ecosystem functions
(e.g., carbon sequestration). The EPA understands the importance of
prescribed fire which mimics a natural process necessary to manage and
maintain fire-adapted ecosystems and climate change adaptation, while
reducing risk of uncontrolled emissions from catastrophic wildfires,
and is committed to working with federal land managers, tribes, and
states to effectively manage prescribed fire use to reduce the impact
of wildfire related emissions on PM2.5.
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    \91\ For example, see ``miscellaneous'' category of direct
PM2.5 emissions in Table 1.
    \92\ Indeed, ``fire policy that focuses on [wildfire]
suppression only, delays the inevitable, promising more dangerous
and destructive future . . . fires.'' Stephens, SL; Agee, JK; Fule,
PZ; North, MP; Romme, WH; Swetnam, TW. (2013). Managing Forests and
Fire in Changing Climates. Science 342: 41-42.
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    If wildfire impacts are significant, contributing to exceedances of
the standard, the EPA proposes that air agencies should consider RACM
for this source. Fires play an important ecological role across the
globe, benefiting those plant and animal species that depend upon
natural fires for propagation, habitat restoration, and reproduction.
Fires are one tool that can be used to reduce fuel load, unnatural
understory, and tree density, helping to reduce the risk of
catastrophic wildfires. Some wildfires and the use of prescribed fire
can influence the occurrence of catastrophic wildfires which may reduce
the probability of fire-induced smoke impacts and subsequent health
effects. RACM must be determined for each area on a case-by-case basis.
Possible RACM for wildfire may include measures that reduce wildland
fuels through fuels management, including the use of prescribed fire
and possibly allowing some wildfire to occur naturally in systems that
are ecologically fire

dependent. Where appropriate, states, land managers, and landowners may
consider developing plans to ensure that fuel accumulations are
addressed and fuels management efforts, including prescribed fire, are
not delayed. The EPA also proposes that air agencies should consider
RACM for managing emissions from prescribed fires (including those
prescribed fires conducted to reduce future wildfire emissions).
Information is available from the DOI and the USDA Forest Service on
smoke management programs and basic smoke management practices. The EPA
requests comment on the concept of, and practical considerations
associated with, RACM for wildfire and prescribed fire, including such
issues as how such measures can be characterized in the emissions
inventory and attainment demonstration and made federally enforceable
for adoption in a SIP.
    (4) RACT for EGUs. Through guidance in the preamble to the 2007
PM2.5 Implementation Rule, the EPA established a rebuttable
presumption that compliance with the CAIR would satisfy RACM and RACT
requirements for SO2 and NOX emissions from EGUs
in states participating in the CAIR cap-and-trade program for such
emissions.\93\ The EPA indicated that states could presume that EGUs
located within a given nonattainment area were meeting the RACM and
RACT requirements, based solely upon a regional program that imposed
controls for SO2 and NOX emissions from sources
both within and outside designated nonattainment areas.
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    \93\ See the Federal Register published on April 25, 2007 (72 FR
20586, 20623, 20624 and 20625).
---------------------------------------------------------------------------

    In June 2007, the EPA received a petition for reconsideration
questioning the legality of this presumption, which the D.C. Circuit
later found to be unlawful in the context of a similar presumption in
the Phase 2 Ozone (NAAQS) Implementation Rule.\94\ The agency granted
the petition for reconsideration in 2011 and proposed to withdraw from
the 2007 PM2.5 Implementation Rule any presumption that
compliance with the CAIR automatically satisfies RACM and RACT
requirements for SO2 and NOX emissions from EGUs
located in nonattainment areas for the 1997 PM2.5
NAAQS.95 96 In that proposal, the EPA explained that given
the explicit wording of section 172(c)(1) that sources ``in the area''
(i.e., in the nonattainment area) must at a minimum adopt RACT controls
for that area, the agency believes that it is no longer appropriate to
presume that this requirement is satisfied merely based upon the
participation of a source in a regional cap-and-trade program. Indeed,
implicit in a regional cap-and-trade program is that some sources,
including those located within nonattainment areas, may elect to buy
allowances in lieu of controlling emissions in order to meet the
regional emissions reductions requirements.
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    \94\ See ``Petition for Reconsideration,'' filed by Paul Cort,
Earthjustice, on behalf of the American Lung Association, Medical
Advocates for Healthy Air, Natural Resources Defense Council, and
the Sierra Club (June 25, 2007). A copy of the petition is in the
docket for this action. The EPA's decision to grant the petition for
reconsideration on the issue of the CAIR being presumptively equal
to RACT for EGUs was in part based on a D,C. Circuit decision
related to a similar issue. Specifically, the Court decided that the
provisions in the Phase 2 Ozone Implementation Rule indicating that
a state need not perform (or submit) a NOX RACM/RACT
analysis for EGU sources subject to a cap-and-trade program that
meets the requirements of the NOX SIP Call are
inconsistent with the statutory requirements of section 172(c)(1).
The Court concluded that the phrase ``in the area'' means that
reductions must occur from sources within the area and ``reductions
from outside the nonattainment area do not satisfy the
requirement.'' See NRDC v. EPA, 571 F.3d 1245 (D.C. Cir. 2009).
    \95\ Letter dated April 25, 2011, from former Administrator Lisa
Jackson to Paul Cort, Earthjustice. A copy of this letter is located
in the docket for this action.
    \96\ 79 FR 32892 (June 9, 2013).
---------------------------------------------------------------------------

    Accordingly, the EPA is not proposing any rebuttable presumption
that the CAIR or any other regional control strategy constitutes RACM
or RACT for EGUs or any other source category. Instead, the EPA is
clarifying that in order to meet the RACM and RACT requirements for the
PM2.5 NAAQS, states should evaluate EGU sources for RACM and
RACT level controls just like any other source category, and not merely
presume for EGUs located in a nonattainment area that compliance with a
cap-and-trade program, including the CAIR or any other program, would
satisfy their obligation to implement RACM and RACT. As required by the
CAA, states are required to analyze what constitutes RACM and RACT for
EGUs in each nonattainment area.
    Step 2: Determine whether an available control measure or
technology is technologically feasible. Once a state has identified
existing and potential control measures and technologies for sources of
direct PM2.5 and PM2.5 precursors in the
nonattainment area(s), it must evaluate these controls to determine if
any of those controls would be technologically infeasible in the
particular nonattainment area.
    i. Stationary sources. With respect to the technological
feasibility of control technologies for stationary sources, the EPA has
a longstanding approach to evaluating facts relevant to this criterion
under subpart 4.\97\ The EPA interprets the term technological
feasibility to include consideration of factors such as a source's
processes and operating procedures, raw materials, physical plant
layout, and potential environmental impacts such as increased water
pollution, waste disposal and energy requirements. For example, the EPA
recognizes that the process, operating procedures and raw materials
used by a source can affect the feasibility of implementing process
changes that reduce emissions and can also affect the selection of add-
on emissions control equipment. The feasibility of modifying processes
or applying control equipment also can be influenced by the physical
layout of the particular plant, if the physical space available in
which to implement such changes limits the choices. The EPA proposes to
retain its longstanding practice that a state should be allowed to
consider such factors in order to eliminate from consideration control
measures that are not technologically feasible to implement.\98\
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    \97\ See the Federal Register published on April 16, 1992 (57 FR
13498, 13540 and 13541).
    \98\ Addendum to the General Preamble, 59 FR 41998 (August 16,
1994), at page 42013. Guidance is provided in the context of Serious
area BACM determination, but the EPA is proposing to apply it here
for Moderate area RACM determinations.
---------------------------------------------------------------------------

    ii. Area and mobile sources. With respect to determining whether a
given control measure might not be technologically feasible for an area
or mobile source, the EPA also proposes to retain its longstanding
practice that a state may consider relevant factors in conducting its
analysis, such as the social acceptability of the measure (e.g.,
residential woodstove change-out programs rely in large part on the
willingness of individual citizens to participate in such a program)
and local circumstances, such as the condition and extent of needed
infrastructure, population size, or workforce type and habits, which
may prohibit certain potential control measures from being
implementable.
    The EPA seeks comment on the factors described above for states to
consider when determining whether a control technology or measure is
technologically feasible.
    Step 3: Determine whether an available control measure or
technology is economically feasible. The EPA has a longstanding
interpretation of the term ``economic feasibility'' in the context of
evaluating potential RACM and RACT which involves considering the cost
of reducing emissions and the difference between the cost of an
emissions reduction measure at a particular source

and the cost of emissions reduction measures that have been implemented
at other similar sources in the same or other areas.\99\ Absent other
indications, the EPA presumes that it is reasonable for similar sources
to bear similar costs of emissions reductions. Economic feasibility of
RACM and RACT is thus largely informed by evidence that other sources
in a source category have in fact applied the control technology,
process change or measure in question in similar circumstances.
---------------------------------------------------------------------------

    \99\ See the Federal Register published on April 16, 1992 (57 FR
13498, 13540 and 13541).
---------------------------------------------------------------------------

    In the preamble to the 2007 PM2.5 Implementation Rule,
the EPA provided guidance on how to interpret the term ``economic
feasibility'' which deviated from the agency's longstanding
interpretation of the term. After promulgating the final rule, the EPA
received and granted a petition for reconsideration on issues related
to the agency's revised approach to interpreting the term
``economically feasible.'' 100 101 Consistent with the EPA's
granting of that petition for reconsideration, the EPA is proposing in
this action an interpretation of economic feasibility that is
consistent with the EPA's longstanding interpretation of what factors
are appropriate for consideration of economic feasibility in a RACM and
RACT analysis, instead of that adopted in the 2007 PM2.5
Implementation Rule.
---------------------------------------------------------------------------

    \100\ ``Petition for Reconsideration,'' filed by Paul Cort,
Earthjustice, on behalf of the American Lung Association, Medical
Advocates for Healthy Air, Natural Resources Defense Council, and
the Sierra Club (June 25, 2007). A copy of the petition is in the
docket for this action.
    \101\ Letter dated April 25, 2011, from former Administrator
Lisa Jackson to Paul Cort, Earthjustice. A copy of this letter is
located in the docket for this action.
---------------------------------------------------------------------------

    Specifically, the EPA proposes that for each technologically
feasible control measure or technology, a state must evaluate the
economic feasibility of the measure or control, through consideration
of the capital costs, operating and maintenance costs, and cost
effectiveness (i.e., cost per ton of pollutant reduced by that measure
or technology) associated with such measure or control. Furthermore,
the EPA proposes that a state may not reject a technologically feasible
control measure or technology as being economically infeasible if such
a measure or technology has been implemented at other similar sources
(i.e., at sources that would be included in the same source category in
the emissions inventory data collection process), unless the state
provides an adequate justification that clearly explains the specific
circumstances of the source or sources in the nonattainment area that
make such a measure or technology economically infeasible in that
particular area.
    The EPA believes that it is appropriate for states to give
substantial weight to cost effectiveness in evaluating the economic
feasibility of an emission reduction measure or technology. The cost
effectiveness of a measure is its annualized cost ($/year) divided by
the emissions reduced (tons/year) which yields a cost per amount of
emission reduction ($/ton). Cost effectiveness provides a relative
value for each emissions reduction option that is comparable with other
options and, in the case of control technologies, other facilities.
    The EPA also seeks comment on an alternative cost effectiveness
metric that would allow a state to take into account the effect of
controlling a particular precursor on reducing PM2.5
concentrations in the area. Such a cost effectiveness metric would be
the annualized cost ($/year) of a control measure divided by the
emissions reduced (tons/year) multiplied by the amount of reductions
needed in the precursor emissions to yield 1 [mu]g/m\3\ reduction in
PM2.5 ($/([mu]g/m\3\)). Such a metric would allow a state to
compare the relative cost effectiveness associated with each measure
toward the attainment goal for the nonattainment area. The EPA notes
the difficulty in determining the appropriate value to relate precursor
reductions to reductions in ambient PM2.5 concentrations,
and therefore seeks comment on the appropriateness of this approach and
how a state might demonstrate the validity of the input values it
chooses to use.
    In considering what level of control is reasonable, the EPA is not
proposing a fixed dollar per ton cost threshold for economic
feasibility of controls identified as potential RACM and RACT. In
addition, if a state contends that a source-specific control-level
should not be established because the source(s) cannot afford the
control measure or technology that is demonstrated to be economically
feasible for other sources in its source category, the EPA proposes
that the state must support the claim with information regarding the
impact of imposing the identified control measure or technology on the
following financial indicators, to the extent applicable:
    1. Fixed and variable production costs ($/unit)
    2. Product supply and demand elasticity
    3. Product prices (cost absorption vs. cost pass-through)
    4. Expected costs incurred by competitors
    5. Company profits
    6. Employment costs
    7. Other costs (e.g., for RACM implemented by public sector
entities).\102\
---------------------------------------------------------------------------

    \102\ These long-standing factors were established in EPA
guidance in 1992 and are applicable to implementation programs for
all NAAQS pollutants. See the appendices to the General Preamble, 57
FR 18070 (April 28, 1992).
---------------------------------------------------------------------------

    The EPA seeks comment on the factors described above for states to
consider when determining whether a control technology or measure is
economically feasible.
    Step 4: Determine the earliest date by which a control measure or
technology can be implemented in whole or in part. CAA section
189(a)(1)(C) requires that the attainment plan for a Moderate
PM2.5 nonattainment area provide for the implementation of
RACM and RACT no later than 4 years after designation. The agency has
long interpreted the term ``implement'' to mean that a control measure
or technology has not only been submitted to the EPA for approval as
part of a SIP but has also been built, installed and/or otherwise
physically manifested, and is achieving the intended emissions
reductions, and the EPA proposes to retain such a definition in this
rule. See proposed 40 CFR 51.1000. However, the EPA recognizes that a
state may be able to implement a given control measure only partially
within 4 years after designation. The EPA addressed this situation in
the General Preamble, stating: ``It is important to note that a State
should consider the feasibility of implementing measures in part when
full implementation would be infeasible.'' \103\ This guidance endorses
the notion that a state should not reject an otherwise technologically
and economically feasible control measure or technology as RACM or RACT
even if it can be only partially implemented within the statutory 4-
year timeframe following designation of the area. Instead, the EPA
interprets the statute to require states to adopt as RACM and RACT that
portion of a control measure or technology that can feasibly be
implemented within 4 years of the effective date of designation. For
instance, if paving unpaved roads is a control measure that is
technologically and economically feasible in a nonattainment area but a
state cannot pave all roads within 4 years of designation, the state
must adopt as RACM a measure that requires paving of that portion of
roads that the state could feasibly accomplish within 4 years if

such a measure is needed for timely attainment of the PM2.5
NAAQS in the area.
---------------------------------------------------------------------------

    \103\ 57 FR 13498 (April 16, 1992), at page 13541.
---------------------------------------------------------------------------

    The EPA thus proposes that a state must identify those
technologically and economically feasible control measures and
technologies that it can implement fully or partially within 4 years of
designation of its Moderate PM2.5 nonattainment area.
Depending on the severity of the PM2.5 nonattainment problem
in the area, some or all of these measures identified as implementable
within 4 years may be needed in order to bring the area into attainment
as expeditiously as practicable. These measures will satisfy the EPA's
criteria for RACM and RACT if the state determines, through its
attainment demonstration that it needs to implement them to achieve
timely attainment for the area.
    In addition, the EPA proposes that a state must separately identify
those technologically and economically feasible control measures that
can only be implemented after the statutory window for implementing
RACM and RACT. The statutory 4-year timing requirement for implementing
RACM and RACT under section 189(a)(1)(C) limits the control measures
and technologies that can qualify as RACM and RACT for a Moderate
PM2.5 nonattainment area. However, the statutory requirement
of CAA 172(c)(6) also requires states to implement ``other measures''
necessary to provide for timely attainment in an area. The EPA proposes
that among such other measures should be ``additional reasonable
measures,'' which would be those measures and technologies that are
otherwise technologically and economically feasible but can only be
implemented in whole or in part later than 4 years after designation
and initiated no later than the beginning of the sixth calendar year
following designation of the area.\104\ Such additional reasonable
measures would necessarily be implemented on sources in the
nonattainment area. However, the EPA interprets the ``other measures''
required under section 172(c)(6) to apply to stationary, area and
mobile sources located outside of the nonattainment area but within the
state if the application of reasonable control measures on such sources
would facilitate attainment of the PM2.5 NAAQS in the
nonattainment area. See proposed 40 CFR 51.1009(b).
---------------------------------------------------------------------------

    \104\ With respect to ``partial measures'' under this proposed
approach, the EPA would require that a state implement as RACM that
portion of any control measure determined to be technologically and
economically feasible and implementable within 4 years after
designation of a nonattainment area. The state would then be
required to implement as an additional reasonable measure that
portion of the same control measure that can be implemented starting
4 years from designation through the sixth calendar year following
designation.
---------------------------------------------------------------------------

    Step 5: Model to determine the attainment date that is as
expeditious as practicable and select the control measures necessary to
achieve attainment and meet statutory requirements for control
measures. Section 189(a)(1) of the CAA establishes a requirement that
the attainment plan for a Moderate PM2.5 nonattainment area
must demonstrate either that an area can attain the relevant NAAQS by
the applicable attainment date or that it is impracticable for the area
to do so. As noted previously, for Moderate PM2.5
nonattainment areas, the ``applicable attainment date'' is as
expeditious as practicable, but no later than the end of the sixth
calendar year after designation as nonattainment. A complete discussion
of the EPA's proposed requirements for attainment demonstration
modeling is presented in Section IV.E of this preamble. However, one of
the key features of attainment demonstration modeling is that it
provides a means of synthesizing the effects of emissions reductions
from all existing and potential new control measures identified for
sources in a given nonattainment area on overall air quality in that
area. States will be required to use the results of their attainment
demonstration modeling to identify the appropriate combination of
reasonable control measures for sources in their Moderate
PM2.5 nonattainment area and any other control measures
needed on sources outside the nonattainment area to ensure expeditious
attainment of the relevant NAAQS in the area and to meet the statutory
requirements of sections 189(a)(1)(B) and 172(c)(6) as explained
below.\105\
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    \105\ Note that under section 110(l) of the CAA, after a state
has adopted a control measure into the SIP for an attainment
demonstration, it may remove or modify a measure if the state
demonstrates to the satisfaction of the EPA that such removal or
modification will not interfere with any applicable requirement of
the CAA, such as attainment of the PM2.5 NAAQS or meeting
RFP requirements.
---------------------------------------------------------------------------

    Step 5a: If the state can demonstrate attainment in the area by the
statutory attainment date for a Moderate area, then the state must
implement those control measures needed for expeditious attainment of
the NAAQS in the area. If a state determines that a Moderate
nonattainment area can attain the PM2.5 NAAQS by the
statutory attainment date, the state must adopt and implement any
technologically and economically feasible control measures that are
necessary to ensure that the area will attain the NAAQS as
expeditiously as practicable. The EPA will consider any such measures
that can be implemented within 4 years of designation of the area to
fulfill the RACM and RACT requirements for the area. In addition, the
EPA will consider any such measures that can only be implemented
between 4 years and the sixth calendar year after designation to meet
the requirements of section 172(c)(6) as ``additional reasonable
measures'' for the area and necessary to demonstrate timely attainment
under section 189(a)(1)(B).
    Under this approach, the state may reject any otherwise
technologically or economically feasible measures that are not needed
to demonstrate attainment or that will not advance the attainment date
by at least 1 year. That is, for a Moderate area that can demonstrate
attainment by the statutory Moderate area attainment date, the EPA
proposes to define as ``reasonable'' only those technologically and
economically feasible measures that are necessary for expeditious
attainment of the NAAQS, as the CAA does not require a state to adopt
measures that are not needed for expeditious attainment in a Moderate
PM2.5 nonattainment area. Thus, a state may exclude those
otherwise reasonably available measures that, if adopted and considered
collectively, would not advance the attainment date for the area by at
least 1 year, so long as the state can demonstrate attainment as
expeditiously as practicable and no later than the statutory Moderate
area attainment date. See proposed 40 CFR 51.1009(a)(4)(i).
    The EPA recognizes that identifying which measures could not
collectively advance the attainment date for a Moderate area by at
least 1 year may be an iterative process that requires additional
analysis and/or modeling. The agency believes that such effort is
reasonable for a state seeking to demonstrate the lack of need for
certain controls that are determined to be technologically and
economically feasible in light of the requirement for expeditious
attainment in a given Moderate nonattainment area. The basis for
deciding that it would be reasonable not to require imposition of
otherwise available and appropriate controls because they would not be
needed for attainment, or would not advance attainment, requires a
suitably robust analysis and explanation.
    Step 5b: If the state cannot demonstrate attainment by the
statutory attainment date for a Moderate area, then the state must
adopt all reasonable control measures. As noted elsewhere in

this section, section 189(a)(1)(B) of the CAA requires a state to
submit as part of the attainment plan either a demonstration that the
plan will provide for attainment of the relevant NAAQS by the
applicable attainment date, or a demonstration that attainment by such
date is ``impracticable.'' This subpart 4 requirement anticipates that
not all nonattainment areas initially classified as Moderate will
necessarily be able to attain by the latest statutory attainment date
for Moderate areas, and it incorporates the concept of an
``impracticability demonstration'' for such areas.\106\ The CAA is thus
structured to provide that Moderate areas that cannot timely attain the
NAAQS through the required elements of a Moderate area attainment plan
will be reclassified to Serious and will have to meet additional
control requirements beyond those that are ``reasonable'' to assure
attainment of the NAAQS by a later date that is as expeditious as
practicable.
---------------------------------------------------------------------------

    \106\ The concept of an ``impracticability demonstration'' is
established in section 188(b), which addresses reclassifying
Moderate PM2.5 areas to Serious. Section 188(b)(1)
describes the EPA's discretionary authority to reclassify an area
upon a determination that an area cannot practicably attain by the
Moderate area attainment date. More relevant to this determination,
however, section 189(a)(1)(B) specifically provides for submission
of a demonstration addressing this concept in the case of Moderate
areas that cannot attain the NAAQS by the applicable attainment
date.
---------------------------------------------------------------------------

    Existing guidance in the General Preamble on implementing this
section of the CAA states that ``the EPA believes it is reasonable for
all available control measures that are technologically and
economically feasible to be adopted for areas that do not demonstrate
attainment [by the applicable attainment date].'' \107\ The EPA
maintains that it is reasonable to require a state to model the effects
of emissions reductions from all technologically and economically
feasible controls identified by the state for sources in a
nonattainment area before asserting a claim that the area cannot
practicably attain the relevant NAAQS by the Moderate area attainment
date. However, the magnitude of certain PM2.5 precursor
emissions and/or local atmospheric conditions of some PM2.5
nonattainment areas may render certain technologically and economically
feasible control measures ineffective in reducing ambient
PM2.5 levels. Therefore, even in a Moderate PM2.5
nonattainment area that cannot practicably attain the relevant NAAQS by
the statutory attainment date, the EPA believes that it may not be
reasonable in all cases to require that a state implement all
technologically and economically feasible control measures identified
for sources in the area.
---------------------------------------------------------------------------

    \107\ 57 FR 13498 (April 16, 1992), at page 13544.
---------------------------------------------------------------------------

    Consistent with the EPA's long-standing interpretation that subpart
4 Moderate area control requirements must be reasonable, the EPA
proposes that, for a Moderate PM2.5 nonattainment area that
cannot practicably attain the NAAQS by the statutory attainment date, a
state must adopt and implement all technologically and economically
feasible measures identified for sources in the area, except for any
such measures that collectively will not effectively reduce ambient
PM2.5 concentrations. See proposed 40 CFR 51.1009(a)(4)(ii).
The EPA views this approach as similar to the agency's approach of
allowing states to reject any otherwise technologically or economically
feasible measures that are not needed to demonstrate attainment and
that will not advance the attainment date by at least 1 year for
nonattainment areas for which states can demonstrate attainment by the
statutory attainment date. Once again, the EPA recognizes that
identifying which measures collectively will not effectively reduce
ambient PM2.5 concentrations will likely be an iterative
process that requires specific analysis, potentially including
modeling. However, the agency believes that such effort is appropriate
for a state seeking to demonstrate the lack of need for certain
controls that are determined to be technologically and economically
feasible in a Moderate nonattainment area that cannot practicably
attain the relevant PM2.5 NAAQS by the latest statutory
Moderate area attainment date. The basis for establishing that it would
not be reasonable to require imposition of otherwise available and
appropriate controls because they would not be effective in reducing
ambient PM2.5 concentrations requires an adequately robust
analysis and explanation.
    The EPA also proposes an alternative approach to identifying all
reasonable control measures for a Moderate nonattainment area that
cannot practicably attain the PM2.5 NAAQS by the end of the
sixth calendar year following designation. Under this alternative,
states would be required to implement all technologically and
economically feasible control measures that they have identified for
sources of direct PM2.5 emissions and sources of emissions
of significant PM2.5 precursors in the area. The EPA
believes that this interpretation would be consistent with the agency's
previous guidance in the General Preamble and is compelled by the
language of section 189(a)(1)(C), which separately requires a state to
submit a Moderate area attainment plan and meet the RACM and RACT
requirement, even if the state submits a demonstration that it cannot
attain the NAAQS through those measures by the applicable attainment
date. In addition, as with a Moderate PM2.5 nonattainment
area which a state demonstrates can attain the NAAQS by the end of the
sixth calendar year following designation, the EPA interprets the
provisions of section 172(c)(6) to require that such an area must
implement all additional reasonable measures that it can implement
through the sixth calendar year following designation of the area, in
addition to those measures meeting the definition of RACM and RACT, in
order to make progress toward attainment after the end of the fourth
year following designation.
    As described in Section III of this preamble, the EPA is proposing
three options for implementing CAA requirements applicable to
PM2.5 precursors in the context of attainment planning and
NNSR permitting. Proposed precursor Options 2A and 2B would provide an
opportunity for a state to demonstrate that emissions of a particular
precursor from all sources located in a Moderate PM2.5
nonattainment area do not contribute significantly to ambient
PM2.5 levels that exceed the standard in the area, or
reductions of which will not be effective in reducing ambient
PM2.5 concentrations, in which case the state would not be
required to identify or otherwise evaluate control measures for the
particular precursor. Under proposed precursor Options 1 and 3, on the
other hand, states would rely on their control strategy analyses (e.g.,
for Moderate nonattainment areas, analyses to determine RACM and RACT
and additional reasonable measures) to identify whether and/or which
controls on sources of PM2.5 precursors are ``reasonable.''
The EPA believes that if proposed precursor Option 1 or 3 is finalized,
it would be most appropriate to finalize the first approach to
identifying reasonable control measures for Moderate areas that cannot
practicably attain the NAAQS by the statutory attainment date, since
states would not have an opportunity prior to evaluating the specific
control measures for sources of PM2.5 precursors in the
nonattainment area to demonstrate that controlling all sources of a
particular precursor would not be effective in reducing ambient
PM2.5 levels in the area. Likewise, if the agency finalizes
proposed precursor Options 2A or 2B, the EPA believes that it would be
most appropriate to finalize the alternative

proposed approach of requiring a state to implement all technologically
and economically feasible measures identified by the state for sources
in the area that can be implemented by the end of the sixth calendar
year following designation if the state demonstrates that the area
cannot practicably attain the NAAQS by the statutory attainment date,
since the ``measures identified by the state'' would already implicitly
exclude control measures on sources of any ``insignificant'' precursor.
The EPA seeks comment on the two proposed approaches to selecting RACM
and RACT and additional reasonable measures for Moderate nonattainment
areas that cannot practicably attain the NAAQS by the statutory
attainment date, and on the EPA's evaluation of the compatibility of
these proposed approaches with the agency's proposed precursor options.
    The EPA's proposed analytical process for determining RACM and RACT
is intended to result in a comprehensive list of such technologically
and economically feasible controls that would include local and state
measures that could achieve emissions reductions from sources within
the area, beyond those that could or would be achieved through regional
or national measures. Furthermore, the EPA is proposing to require that
the Moderate area attainment plan must include modeling of all RACM and
RACT and additional reasonable measures, and other state, regional and
federal measures, to demonstrate that a state will not be able to
attain the NAAQS by the end of the sixth calendar year after
designation due to the severity of nonattainment in the area and/or due
to the lack of availability or feasibility of implementing controls in
the area by such date.
    Subpart 4 requires that Moderate areas that cannot or do not meet
the Moderate area attainment date be reclassified as Serious
nonattainment areas, in which case sources in the areas are then
subject to BACM and BACT requirements. In the General Preamble, the EPA
indicated that ``it may be reasonable, in some limited circumstances,
for States to consider the compatibility of RACM and RACT with the BACM
and BACT that will ultimately be implemented under the Serious area
plans for those areas.'' \108\ Furthermore, for such areas that do not
meet the Moderate area attainment date, the EPA indicated that ``in the
case of RACM for area sources, EPA anticipates that any future
implementation of BACM for these sources will be additive to, and hence
compatible with, RACM. This is because BACM will generally consist of a
more extensive implementation of the RACM measures . . . Since EPA
anticipates that RACM and BACM for these sources will be compatible,
the SIP's (sic) for these areas should reflect the application of
available control measures to existing sources in moderate
nonattainment areas as determined by the analysis described . . . for
RACM.'' \109\ The EPA believes that a state should consider selecting
and implementing controls that may qualify as BACM or BACT in a
Moderate nonattainment area as part of their RACM and RACT analysis if
they have reason to suspect that the area may not be able to attain the
NAAQS by the applicable Moderate area attainment date as long as the
control can be implemented by the statutory Moderate area attainment
date. Early adoption of controls that would constitute BACM or BACT
could be more efficient and could further the objectives of attaining
the NAAQS expeditiously to protect public health and the environment.
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    \108\ Ibid. at 13544.
    \109\ Ibid.
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3. RACM and RACT and Additional Reasonable Measures Submission
Requirements
    To ensure that attainment plan submissions contain the necessary
supporting information to enable the EPA to review and approve a
state's evaluation and selection of measures that constitute RACM and
RACT in a given nonattainment area, the EPA proposes to require under
the authority of section 301(a) that a state must submit the following
information as part of its submission:
     A list of all source categories, sources and activities in
the nonattainment area that emit direct PM2.5 or any
PM2.5 precursor (for multi-state nonattainment areas, this
would include source categories, sources and activities from all states
which make up the area);
     For each source category, source or activity in the
nonattainment area, an inventory of direct PM2.5 emissions
and emissions of all PM2.5 precursors;
     For each non-de minimis source category, source or
activity in the nonattainment area, a comprehensive list of potential
control measures considered by the state for the nonattainment area;
110 111
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    \110\ If the EPA finalizes proposed precursor Option 2A or 2B,
which would effectively allow a state to demonstrate that a given
precursor does not contribute significantly to PM2.5
concentrations in a nonattainment area, then this step would require
potential control measures only for sources of direct
PM2.5 and precursors not exempted from further analysis.
    \111\ Menu of Control Measures document available at http://www.epa.gov/air/criteria.html.
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     For each potential control measure considered by the state
but eliminated from further consideration due to a determination by the
state that the control measure or technology was not technologically
feasible, a narrative explanation and quantitative or qualitative
supporting documentation to justify the state's conclusion;
     For each technologically feasible emission control measure
or technology, the state must provide the following information
relevant to economic feasibility: (1) The control efficiency by
pollutant; (2) the possible emissions reductions by pollutant; (3) the
estimated cost per ton of pollutant reduced; and, (4) a determination
of whether the measure is economically feasible, with narrative
explanation and quantitative supporting documentation to justify the
state's conclusion.
     For each technologically and economically feasible
emission control measure or technology, the date by which the
technology or measure could reasonably be implemented.
    Each of these elements will provide information needed by the EPA
to evaluate correctly and efficiently whether the state is meeting the
statutory requirements for an attainment plan, and in particular
meeting the statutory requirement for states to implement RACM and RACT
on sources within the nonattainment area. The EPA recognizes that the
base year emissions inventory for the area that the state submits in
conjunction with its attainment plan will likely contain some of the
information proposed to be required under the first two items in this
list. However, the EPA believes that it is incumbent on the state to
ensure that the information needed for the EPA to evaluate the state's
RACM and RACT analysis is presented more specifically as part of the
RACM and RACT analysis and in a format that provides transparency,
consistency and the ability for another party to evaluate the state's
analysis effectively. For this reason, the EPA is including emissions
inventory information specifically relevant to the RACM and RACT
element of the state's attainment plan.
4. Criteria for Effective Regulations To Implement RACM and RACT and
Additional Reasonable Measures
    After a state has identified a particular control measure as RACM
or RACT or additional reasonable measure for a particular nonattainment
area, it must

then implement that measure through a legally enforceable mechanism
that will be included in the SIP (e.g., a state rule that the EPA will
approve as a part of the federally enforceable SIP for the state). The
EPA is proposing that in order for the EPA to be able to approve any
such measure as part of the SIP, the state would have to provide
information to meet the following four criteria. These criteria are
similar to the criteria finalized as part of the remanded 2007
PM2.5 Implementation Rule.
    First, the base year emissions from the source or group of sources
to which the control measure applies and the future year projected
emissions from those sources once controlled must be quantifiable so
that the projected emissions reductions from the sources can be
attributed to the specific measures being implemented. It is important
that the emissions from the source category in question are accurately
represented in the base year inventory so that emissions reductions are
properly calculated. In particular, it is especially important to
ensure that both the filterable and condensable components of direct
PM2.5 emissions are accurately represented in the base year.
    Second, the control measures must be enforceable. This means that
they must specify clear, unambiguous and measurable requirements. The
measurable requirements for larger emitting facilities must include
periodic source testing, monitoring or other viable means to establish
whether the affected source meets the applicable emission limit.
Additionally, to verify the continued performance of the control
measure, specific emissions monitoring programs appropriate for the
type of control measure employed and the level of emissions must be
included to verify the continued performance of the control measure.
The control measures and monitoring program must also have been adopted
according to proper legal procedures.
    Third, the results of application of the control measures must be
replicable. This means that where a rule contains procedures for
interpreting, changing or determining compliance with the rule, the
procedures are sufficiently specific and objective so that two
independent entities applying the procedures would obtain the same
result.
    Fourth, the control measures must be accountable. This means, for
example, that source-specific emission limits must be permanent and
must reflect the assumptions used in the attainment plan for the area,
including the modeling conducted in conjunction with the attainment
demonstration. It also means that the attainment plan must establish
requirements to track emissions changes at sources and provide for
corrective action if emissions reductions are not achieved according to
the plan.
    The EPA seeks comment on these criteria for approval of any control
measures adopted by a state for a Moderate area to assure that such
measures are legally enforceable.
5. Determination of RACM and RACT and Additional Reasonable Measures in
Multi-State Nonattainment Areas
    States in multi-state nonattainment areas will need to consult with
each other on appropriate control measures for the shared nonattainment
area. The agency anticipates that states could decide upon RACM and
RACT and additional reasonable measures that differ from state to state
in a shared nonattainment area, based upon each state's determination
of the most effective strategies given the relevant mixture of sources
and potential controls in the respective states' portions of a shared
nonattainment area. As long as each state can adequately demonstrate
that its chosen attainment strategy, including its selection and
adoption of RACM and RACT and additional reasonable measures, will
provide for meeting RFP requirements and for attainment of the NAAQS as
expeditiously as practicable for the nonattainment area at issue, the
EPA anticipates being able to approve individual state plans that may
elect to control a different mix of sources or to implement different
controls, under the proper circumstances. Nevertheless, in evaluating
RACM and RACT and additional reasonable measures for a particular
nonattainment area, states must consider potential reasonable control
measures developed for other areas or other states, and particularly
for other portions of an interstate nonattainment area. In addition,
states in multi-state nonattainment areas must evaluate whether the
reasonable measures each state may have identified as not being
necessary for attainment could collectively advance the attainment date
for the area by at least 1 year. The EPA may consider such measures in
assessing the approvability of each state's individual attainment plan
for a multistate nonattainment area.
6. Environmental Justice Considerations in Developing the Attainment
Plan Control Strategy for a Moderate PM2.5 Nonattainment
Area
    The EPA strongly urges states to consider environmental justice
concerns with respect to any control measures they have identified as
potential RACM or RACT or additional reasonable measures in an area,
particularly to the extent that control measures that a state may be
considering are otherwise approximately equal (in terms of
technological and economic feasibility) but unequal with respect to
their direct or indirect impacts on overburdened populations.\112\ In
such cases, the EPA encourages the state to prioritize imposition of
the control measures that will result in the least possible burden and
greatest degree of health protection for overburdened populations in
the nonattainment area. Section IX of this preamble discusses this and
other possible approaches for states to incorporate ways to address
environmental justice concerns associated with implementation of the
PM2.5 NAAQS in their attainment plans and SIP development
process, and the EPA seeks comment on ways to more fully address such
concerns.
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    \112\ The term ``overburdened populations'' is defined in the
EPA's ``Plan EJ 2014'' to describe the minority, low-income, tribal,
and indigenous populations or communities in the U.S. that
potentially experience disproportionate environmental harms and
risks as a result of greater vulnerability to environmental hazards.
This increased vulnerability may be attributable to an accumulation
of both negative and lack of positive environmental, health,
economic or social conditions within these populations or
communities. For more information on Plan EJ 2014, see: http://www.epa.gov/environmentaljustice/plan-ej/.
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E. Modeling for Attainment Demonstrations

1. Statutory Requirements
    Section 189(a) generally requires a state with a designated
Moderate nonattainment area to submit an attainment plan for such area.
As discussed earlier, section 189(a)(1)(B) more specifically requires
the state to submit an attainment demonstration including air quality
modeling to establish either: (i) That the area will attain the
relevant NAAQS by the applicable attainment date; or, (ii) that it is
impracticable for the area to attain the relevant NAAQS by the
applicable attainment date. For Moderate nonattainment areas, the
attainment date is as expeditiously as practicable, but no later than
the end of the sixth calendar year after designation as nonattainment.
Section 189(a)(2)(B) of the CAA requires states with designated
nonattainment areas to submit attainment plans no later than 18 months
after designation.

2. What is an attainment demonstration?
    Section 189(a)(2)(B) does not define the term ``demonstration'' and
does not specify precisely how a state should make the required
demonstration. Thus, the EPA believes it is necessary to provide more
specific parameters for such demonstrations in order to assure that
they contain the requisite information to allow for meaningful
evaluation of the issues that the demonstrations are intended to
address. An attainment demonstration is a set of analyses that provide
an explanation of how a state will attain the PM2.5 NAAQS by
the applicable attainment date in a particular nonattainment area.\113\
The EPA is proposing that the demonstration must contain: (i) Technical
analyses such as base year and future year modeling of emissions which
identify sources and quantify emissions that are contributing to
violations of the PM2.5 NAAQS; and, (ii) analyses of future
year emissions reductions and air quality improvement resulting from
existing (i.e., already-adopted or ``on the books'') national, regional
and local programs, and potential new local measures needed for
attainment, including RACM and RACT controls for the area. Each state
with a Moderate nonattainment area must submit an attainment plan with
an attainment demonstration that includes analyses supporting the
state's determination of its proposed attainment date. In all cases,
the state must show that the Moderate area will attain the NAAQS as
expeditiously as practicable, but not later than the end of the sixth
calendar year after designation. In order to establish that the
attainment date is as expeditious as practicable, the state must
explain why any control measures adopted in the attainment plan provide
for the most expeditious attainment and, specifically, must demonstrate
that collectively the reasonable measures that were not adopted as RACM
or RACT or additional reasonable measures will not advance the
attainment date by at least 1 year if implemented. See proposed 40 CFR
51.1011(a).
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    \113\ An area is designated nonattainment for either the annual
PM2.5 NAAQS or the 24-hr PM2.5 NAAQS or both.
The attainment demonstration should show that the area is attaining
the form of the NAAQS for which they have been designated
nonattainment.
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    A state may alternatively submit a demonstration that shows that
attainment by the statutory attainment date for a Moderate area is
impracticable.\114\ The statute does not define the term
``impracticable'' in this context, so it is necessary for the EPA to
interpret this term in the context of a submission from the state for
this purpose. In order to support this type of demonstration, the EPA
proposes to require that the state must show that, even if all
technologically and economically feasible controls that can be
implemented within 6 years were implemented, the state could not attain
the NAAQS within the statutory timeframe for a Moderate area. A state
could do this by performing a modeling analysis which projects
emissions to the sixth year after designations in order to predict
future year PM2.5 design values in the area. The projected
emissions would account for all existing federal and state SIP-adopted
regulations on sources outside the nonattainment area that were in
place at the time, plus all measures that were identified as
technologically and economically feasible controls that can be
implemented in the nonattainment area within 6 years of designation
(i.e. all measures that would qualify as RACM or RACT or as additional
reasonable measures), as well as any other reasonable measures
available in the state that could aid in achieving timely attainment.
If the modeling shows that attainment cannot be reached by the end of
the sixth calendar year following designation, then the analysis could
be used to demonstrate that it is impracticable for the area to attain
the relevant NAAQS by the statutory attainment date. Other information
can also be used to support the demonstration, including ambient data
and emissions trends data. States are encouraged to work with their
respective EPA Regional Office to identify appropriate information that
could be used to support an impracticability demonstration. The EPA
emphasizes that states that can make the required showing that a
Moderate nonattainment area cannot attain the NAAQS by the statutory
attainment date are nonetheless required to meet the substantive
requirements for a Moderate area attainment plan, including the
implementation of control measures that are RACM and RACT and
additional reasonable measures in that area.
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    \114\ Pursuant to section 188(b)(1)(B), upon an EPA
determination that attainment by the Moderate date is impracticable,
the EPA shall reclassify the area as Serious within 18 months after
the Moderate area attainment plan due date.
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3. What modeling is required?
    States are required to submit air quality modeling in support of an
attainment demonstration for a Moderate PM2.5 nonattainment
area. Although air quality modeling is not expressly required for a
Moderate area demonstration showing that attainment by the attainment
date is impracticable (per section 189(a)(1)(B)(ii)), the EPA proposes
to interpret the CAA to require air quality modeling similar to that
required for an attainment demonstration in order to demonstrate that
attainment of the relevant PM2.5 NAAQS by the statutory
attainment date is impracticable. Because air quality modeling is a
required element of the attainment demonstration in section
189(a)(1)(B), the EPA believes that it logically follows that similar
modeling should also be required to show that an area will not be able
to attain by the attainment date contemplated by the statute.
    There may be limited cases in which a state may be able to
demonstrate through a rigorous technical analysis with supporting
documentation that attainment by the statutory Moderate area attainment
date is impracticable. Given that the statute may be interpreted as not
requiring air quality modeling for an impracticability demonstration,
the EPA proposes and seeks comment on an alternative option under which
air quality modeling would not be a requirement for a Moderate area
impracticability demonstration. The EPA would recommend that a state
submit modeling as part of any Moderate area impracticability
demonstration, but under this alternative option such modeling would
not be a regulatory requirement.
    Given that secondarily formed PM2.5 (e.g. ammonium
sulfate, ammonium nitrate and SOA) is a large fraction of the total
measured PM2.5 in most PM2.5 nonattainment areas,
the EPA assumes that photochemical grid modeling (which considers
secondary PM2.5 formation) will be needed for a state to
demonstrate attainment with the NAAQS. Most previous PM2.5
attainment demonstrations for both the 1997 and 2006 PM2.5
NAAQS have utilized photochemical grid models. However, in some
nonattainment areas that are dominated by primary PM2.5
emissions (e.g. residential wood smoke), more simplistic dispersion
models, such as a combination of dispersion, receptor and box airshed
models, may suffice to demonstrate that the area will attain the NAAQS.
Regardless of the modeling approach selected to support the attainment
demonstration, the analyses must be based on technically credible
methods and provide for the timely submittal of the attainment
demonstration and implementation of control measures. States should
consult with their respective EPA Regional

Office to determine the appropriate type of modeling demonstration for
the particular nonattainment area.
4. Do states need to develop new modeling for their attainment
demonstrations?
    The EPA believes that the statutory provision requiring attainment
demonstrations for Moderate PM2.5 nonattainment areas to
include air quality modeling can be fulfilled in a variety of ways.
Thus the EPA proposes to allow states to fulfill the statutory modeling
requirement through either locally generated photochemical and/or
dispersion modeling or, with proper justification, through appropriate
regional or national modeling. The EPA seeks comment on what types of
modeling demonstrations should be required to fulfill the CAA
requirement to ``include air quality modeling'' as part of the
attainment demonstrations for Moderate nonattainment areas.
    New modeling analyses that follow the EPA modeling guidance,
conducted by the state for implementing the PM2.5 NAAQS,
will presumably satisfy the attainment demonstration modeling
requirement. However, many areas that were designated as nonattainment
for the 1997 and/or 2006 PM2.5 NAAQS have already invested
considerable resources in local and/or regional PM2.5
modeling analyses. Most states with potential PM2.5
nonattainment areas are already participating in regional modeling
analyses through multi-jurisdictional organizations (MJOs). These MJOs
(e.g. SESARM, LADCO and WRAP) represent most states with
PM2.5 nonattainment areas in the country. There is ongoing
PM2.5 modeling that may provide useful information for state
PM2.5 NAAQS attainment demonstrations.
    In addition to local and regional modeling, the EPA conducts
nationwide modeling (generally limited to the contiguous 48 states) in
support of various national rulemakings. The base and future modeling
year for national rule modeling varies depending on compliance dates
for the rule being analyzed and on when the modeling was conducted. For
example, there are several analyses of recent and ongoing rules which
may provide useful PM2.5 modeling information for state
attainment demonstrations. Among them are modeling to support the 2012
PM2.5 NAAQS review, the final Tier 3 mobile source emissions
standards, and the current ozone NAAQS review.\115\ While the analyses
in these rulemaking actions may not be precisely relevant for the
purposes of a PM2.5 attainment plan, they may nevertheless
provide useful information or input relevant to states developing
attainment plans for the PM2.5 NAAQS. Similar nationwide
modeling efforts may be helpful for purposes of future PM2.5
NAAQS.
---------------------------------------------------------------------------

    \115\ Even though the ozone NAAQS modeling will be focused on
ozone, PM2.5 modeling results will likely be generated
from the analysis in order to inform health benefits calculations.
---------------------------------------------------------------------------

    States may be able to use regional and/or EPA modeling to
demonstrate that specific nonattainment areas will attain the relevant
PM2.5 NAAQS by the applicable attainment date, but states
must evaluate the relevant modeling information to show that it is
suitable for that purpose. For example, the modeling should be
evaluated to show that it is performing adequately for the area; that
the future modeling year is appropriate for the particular attainment
demonstration; and that the base year emissions and projected emissions
and controls adequately represent the base year conditions and
emissions expected to occur in the area in the future. States should
work closely with the appropriate EPA Regional Office to determine what
(if any) existing modeling may be suitable for use in an attainment
demonstration (or an impracticability demonstration) for a Moderate
PM2.5 nonattainment area.
    The EPA requests comment on how states can use existing regional
and/or national modeling to meet their attainment demonstration
requirements. The agency also notes that even when regional or EPA
modeling is available to show that an area is expected to attain the
PM2.5 NAAQS by the applicable attainment date, other CAA
requirements may be difficult to satisfy through the use of regional or
EPA modeling. For example, states may or may not be able to satisfy
their CAA requirements for emissions inventory submittals or RFP
demonstrations by using data derived from MJO or EPA modeling. The
available regional/national modeling may not include an appropriate
base year or future year, and the level of detail or how the emissions
were derived may not be appropriate or compatible with inventories
needed to satisfy specific CAA requirements. States may have to derive
more local specific inventory data, for the appropriate years, to
adequately satisfy these CAA requirements.
    Because it will be challenging for states to prepare new modeling
analyses to meet the submission deadline for the Moderate area
attainment plans, the EPA encourages states to start work on modeling
analyses as soon as possible, in order to ensure that adequate time is
devoted to developing a technically credible attainment demonstration.
States that have the most challenging PM2.5 problems will
likely need to develop new and/or updated photochemical modeling
analyses for their nonattainment areas, with emissions (including
potential new controls) projected to the appropriate future attainment
year.
5. What guidance is available for using models to demonstrate
attainment?
    The procedures for modeling PM2.5 as part of an
attainment demonstration are described in the EPA's ``Guidance on the
Use of Models and Other Analyses for Demonstrating Attainment of Air
Quality Goals for Ozone, PM2.5, and Regional Haze.'' \116\
All modeling in support of an attainment demonstration should be
consistent with the EPA's PM2.5 photochemical modeling
guidance (referenced above) as well as the Guideline on Air Quality
Models (40 CFR part 51, Appendix W).
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    \116\ The 2007 modeling guidance can be found at the following
Web site: http://www.epa.gov/scram001/guidance/guide/final-03-pm-rh-guidance.pdf. As noted, the EPA recently released revised draft
modeling guidance.
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    The PM2.5 attainment demonstration modeling guidance
describes how states can apply air quality models to generate results
needed to demonstrate attainment. These recommendations include
developing a conceptual description of the problem to be addressed;
developing a modeling/analysis protocol; selecting an appropriate model
to support the demonstration; selecting appropriate meteorological
episodes or time periods to model; choosing an appropriate area to
model with appropriate horizontal/vertical resolution; generating
meteorological and air quality inputs to the air quality model;
generating emissions inputs to the air quality model; and, evaluating
performance of the air quality model. After these steps are completed,
the state can apply a model to simulate effects of future year
emissions and candidate control strategies.
    The EPA is not requiring a specific model for use in the attainment
demonstration for the PM2.5 NAAQS. At present, there is no
single model which has been extensively tested and shown to be clearly
superior to other available models. The current modeling guideline, 40
CFR part 51, Appendix W, does not identify a preferred model for use in
attainment demonstrations of the PM2.5 NAAQS. Thus, states
may choose from several alternatives so long as the

alternative is appropriate for the nonattainment area under evaluation.
    In some cases, a state may need to apply multiple models in the
attainment demonstration. In most cases, a photochemical grid model is
needed to predict base and future year concentrations of secondary
PM2.5. Photochemical grid models can also be used to predict
concentrations of primary particulate and are useful in assessing steep
concentration gradients arising from area sources. However, in areas
with high concentrations of primary PM2.5, or strongly
stratified air at the surface, a Gaussian plume model or puff model may
also be needed to more accurately represent steep concentration
gradients (or lack of mixing to the surface) in locations with a large
contribution from a single or multiple primary PM2.5 point
sources or locations in near-road areas. The EPA's attainment
demonstration modeling guidance provides details and recommendations on
using multiple models.
    Models are used to test whether control measures in an attainment
plan are likely to result in attainment of the relevant standard(s).
The attainment demonstration modeling guidance recommends a modeled
attainment test for the annual and 24-hour PM2.5 NAAQS that
uses a combination of ambient PM2.5 and PM2.5
species data and modeled PM2.5 concentrations to estimate
future year air quality. In the recommended attainment test, the state
applies the test at each PM2.5 ambient monitor location
within or near a designated nonattainment area. Models are used in a
relative sense to estimate the response of measured air quality to
future changes in emissions. Future air quality is estimated by
multiplying recent monitored PM2.5 values by the modeled
relative response (percent change) to projected future changes in
emissions. If the future design value at all monitoring locations in
the nonattainment area does not exceed the concentration of
PM2.5 specified in the NAAQS, the area is projected to
attain the NAAQS.
    Because PM2.5 is a mixture of chemical components,
states should use recent observations and modeled responses of major
components of PM2.5 (i.e. sulfate, nitrate, organic carbon,
etc.) to estimate future concentrations of each component.\117\ The
predicted future concentration of PM2.5 is the sum of the
future year predicted component concentrations.
---------------------------------------------------------------------------

    \117\ The exact years of the ``recent'' ambient data are defined
by the base year selected for the modeling. The guidance recommends
using 5 years of ambient data, centered about the base modeling
year.
---------------------------------------------------------------------------

    The attainment demonstration modeling guidance contains additional
details regarding the treatment of PM2.5 and speciation
monitoring data. Because PM species data are not available at each
PM2.5 FRM site, the EPA recommends a methodology which
interpolates species data to each FRM site in order to estimate the
species concentrations in the area. This information, combined with
modeling results, may be used to calculate future air quality at each
FRM monitoring site. The EPA has developed software to perform both the
annual and 24-hour PM2.5 attainment test (including
interpolating PM species data). The software is called the Modeled
Attainment Test Software (MATS) and is available for no cost at: http://www.epa.gov/scram001/modelingapps_mats.htm. The software is provided
to make it relatively easy for states to apply the recommended modeled
attainment test. However, states are not required to use MATS and can
develop their own post-processing software.
    The modeling guidance also describes the opportunity for states to
supplement their modeling with a ``weight of evidence'' demonstration.
States may use other information and analyses, in addition to the
modeled attainment test, to estimate whether future attainment of the
NAAQS in an area is likely. Other analyses may include, but are not
limited to, emissions trends, ambient data trends and analyses, other
modeling analyses, and documentation of other non-modeled emissions
control strategies, including voluntary programs.
    The reliability of tests for estimating future attainment depends
upon having reliable databases for inputs to those tests. The modeling
guidance identifies and prioritizes key data-gathering activities and
analytical capabilities that will increase credibility of analyses used
to estimate if the NAAQS will be attained in the area by the statutory
attainment date.
    The EPA is considering updates to the modeling guidance to address
PM2.5 modeling for the 2012 PM2.5 NAAQS. The
agency released a revised draft modeling guidance for developing
demonstrations to meet PM2.5, ozone, and regional haze air
quality goals in December 2014, and intends to revise the guidance
after considering public comments received.\118\
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    \118\ See ``Draft Modeling Guidance for Demonstrating Attainment
of Air Quality Goals for Ozone, PM2s, and Regional Haze,'' issued by
Richard Wayland, Director of Air Quality Assessment Division, EPA
Office of Air Quality Planning and Standards, to EPA Regional Air
Division Directors, Regions I-X, December 3, 2014. Available at:
http://www.epa.gov/ttn/scram/guidance/guide/Draft_O3-PM-RH_Modeling_Guidance-2014.pdf.
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    The application of air quality models requires a substantial effort
by state and local agencies. Therefore, states should work closely with
their respective EPA Regional Office in executing each step of the
modeling process. Doing so will ensure that states know what EPA
analyses they can rely on, if they wish, to simplify this task, and it
will increase the likelihood of the EPA's approval of a state's
demonstration submitted at the end of the modeling and overall
attainment plan development process.
6. Demonstrating Attainment at Near-Road Monitors
    The 2012 PM2.5 NAAQS final rule contains new
requirements for operating near-road monitors in the largest
metropolitan areas.\119\ The first monitors were required to be in
place as of January 1, 2015 (see Section II of this preamble for more
details). These monitors will not have the requisite 3 years of
monitoring data necessary to calculate a PM2.5 design value
until 2018 at the earliest. Therefore, these data were not available to
inform the first round of initial designations for the 2012
PM2.5 NAAQS and there will be less than 3 years of data
available when the initial attainment demonstrations for Moderate areas
are due in October 2016. As a result of this timing, the agency is
proposing that the initial set of Moderate area attainment
demonstrations will not need to include projected design values for
near-road monitor locations. However, subsequent attainment
demonstrations for the PM2.5 NAAQS (after 2018, when 3 or
more years of complete ambient data are available at near-road
monitors) will need to address those monitor locations in attainment
plans and will need to include a demonstration that those monitor
locations will show attainment of the NAAQS by the applicable statutory
attainment date. The revised modeling guidance document for the
PM2.5 NAAQS includes procedures for applying a dispersion
model or a combination of photochemical grid models and dispersion
modeling to demonstrate attainment at near-road monitor locations.
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    \119\ 78 FR 3085 (January 15, 2013), at page 3283.
---------------------------------------------------------------------------

7. Demonstrating Attainment in Unmonitored Areas
    As explained in the 2012 PM2.5 NAAQS final rule and
summarized in Section II of this preamble, the EPA's

monitoring requirements for PM2.5 are designed to ensure a
robust nationwide monitoring network in both nonattainment and
attainment areas. Air agencies have achieved this by maintaining their
PM2.5 networks in accordance with EPA's network design
criteria. Historically, these criteria provided that CBSAs have at
least one PM2.5 monitoring site located in an ``area-wide''
location of expected maximum concentration (within the CBSA).\120\
Thus, by assuring compliance with the NAAQS at the location of the
expected highest area-wide concentration in the CBSA, air quality is
protected throughout each CBSA. However, due to limited resources,
there are limits to the number of air quality monitors that can be
deployed and it therefore may be useful to consider what, if any,
additional analysis needs there may be as agencies prepare their
attainment plans.\121\
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    \120\ As explained in the final 2012 PM NAAQS rule, the EPA
expects that each CBSA will maintain its existing highest
concentration area-wide monitoring site (referred to as the design
value site), See 78 FR 3085 (January 15, 2013), at page 3240. These
sites were set up during the period of time when the network design
criteria required having at least one site in an area-wide location
of expected maximum concentration. The EPA intends to maintain the
highest priority sites in the existing network, which are often at
the neighborhood scale, as the largest part of the PM2.5
monitoring network to continue to support a number of monitoring
objectives, while also allowing lower value sites to move to near-
road locations as that part of the network is phased in.
    \121\ Annual monitoring network plans and 5 year assessments are
required by regulation in 40 CFR 58.10. The 5 year monitoring
network assessment is a comprehensive evaluation of a monitoring
agency's ambient air monitoring network, while the annual plan
describes the existing network and changes being proposed to support
implementing recommendations from the most recent 5 year assessment
as well as any applicable changes finalized in association with
NAAQS revisions.
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    Under the 2007 PM2.5 Implementation Rule, the EPA
required states to follow existing modeling guidance, which suggested
that a state's PM2.5 attainment plan could be approved if it
demonstrated attainment, through the modeled attainment test, at
monitored locations only. But the guidance also recommended that states
conduct further analyses based on the modeling results to determine
whether there were unmonitored areas that merited additional analysis
or investigation. The guidance further recommended that states either
reduce emissions that, based on these recommended additional analyses,
could cause violations in unmonitored areas, or that they place a new
monitor in such an area. The EPA found that the minimum requirements
for the unmonitored area analysis in the 2007 modeling guidance (and
the 2007 PM2.5 Implementation Rule) were not sufficiently
clear. The EPA is therefore proposing several alternative options in
order to clarify the appropriate treatment of model results in
unmonitored areas for purposes of implementing current and future
PM2.5 NAAQS.
    The EPA is proposing four possible approaches to demonstrating
attainment in unmonitored areas. Option 1 would only require states to
perform the attainment test at locations that have current or recent
FRM and/or FEM monitoring data. The EPA would not require states to
analyze areas that have no monitoring data with which to anchor the
attainment demonstration modeling results. The EPA is proposing this
approach to evaluating monitored and unmonitored areas in order to be
consistent with how attainment of the PM2.5 NAAQS is
determined for purposes of designations and redesignations, and due to
uncertainty in modeled projections in locations where there are no
monitoring data to anchor the future year model results. As discussed
in Section II of this preamble, the EPA promulgates designations for
PM2.5 NAAQS nonattainment areas based primarily on ambient
data measured at FRM and FEM monitors.\122\ Although the EPA considers
other forms of information for purposes of evaluating areas with
sources that contribute to those monitored violations for inclusion
within the nonattainment area boundaries, the fundamental basis for
designating an area as nonattainment for a PM2.5 NAAQS is
the presence of one or more FRM or FEM monitors with data showing
violations of the NAAQS in question. Similarly, determinations of
attainment of the PM2.5 NAAQS for purposes of redesignation
actions are based primarily on monitored data. When all FRM and FEM
monitors in a nonattainment area measure attainment of the
PM2.5 NAAQS, the state is eligible to submit a redesignation
request for the area, assuming that it has complied with all other
applicable requirements for purposes of redesignation. Specifically,
the EPA's approval of a redesignation request is subject to meeting the
requirements of CAA section 107(d)(3)(E). Among those requirements is
that the area has attained the NAAQS. For the PM2.5 NAAQS,
this determination is based on ambient data measured at the FRM and FEM
monitors in the area in question. Thus, neither PM2.5
designations nor redesignations currently take into account information
regarding potential violations of the NAAQS at unmonitored locations
throughout a given area. Therefore, consistent with how
PM2.5 areas are designated and redesignated, the EPA is
first proposing to require that states only show attainment at
PM2.5 FRM and FEM monitoring locations as an element of
their attainment demonstrations for the PM2.5 NAAQS.
---------------------------------------------------------------------------

    \122\ A monitor must have 3 years of quality-assured ambient
data available to be used to calculate a PM2.5 design
value and determine compliance with the NAAQS.
---------------------------------------------------------------------------

    In addition, the ``relative'' attainment test for PM2.5
uses FRM or FEM ambient monitoring data, combined with future year
modeled percentage changes in PM2.5 concentrations, to
project future year design values. Since the attainment test relies on
ambient monitoring data, an analysis of future year concentrations in
unmonitored areas can only be accomplished by interpolating ambient
data to a particular location where there is no existing monitor or
recent monitoring data. Therefore, in the context of an attainment
demonstration, the projection of future year PM2.5
concentrations in unmonitored locations is inherently more uncertain
than projections in monitored locations due to the fact that the
ambient concentrations from which these projections are developed are
unknown in the unmonitored locations.
    Proposed Option 2 for unmonitored area analyses would require the
state to conduct an unmonitored area analysis as part of all attainment
demonstrations (for Moderate and Serious areas) and require the state
to eliminate potential violations in unmonitored areas through
enforceable emissions reductions in the SIP. The requirement would be
based on a premise that states must demonstrate attainment of the NAAQS
in all locations of a nonattainment area, and models can and should be
used for that purpose. Modeled attainment demonstrations using
photochemical grid models provide modeling results for all grid cells
in the nonattainment area. Therefore, notwithstanding the uncertainty
that is inherent to this approach as discussed above, model outputs
(optionally combined with interpolated ambient data) could be used to
derive estimates of PM2.5 concentrations in unmonitored
areas.
    Proposed Option 3 would require states to show attainment at all
current and recent monitoring locations. In addition, states would be
required to provide an unmonitored area analysis as part of all
attainment demonstrations (for Moderate and Serious areas). However,
rather than requiring states to impose additional enforceable emissions
reductions in the SIP to address potential violations in these
locations, states would be required to use the unmonitored area
analysis

results to develop an assessment of the likelihood of violations in
unmonitored areas. This assessment may be especially important in areas
with a relatively sparse PM2.5 monitoring network or in
locations where information such as modeling data, emissions
inventories or non-FEM monitoring data (such as from special purpose
monitors or saturation monitoring studies) may indicate potential high
PM2.5 concentrations in areas that are currently
unmonitored.
    The nature of the assessment of likelihood of violation that is
required under proposed Option 3 would depend on local area modeling,
but could include, as appropriate, elements such as an evaluation of
the emissions inventory (particularly for local direct PM2.5
sources), the existing ambient data for the area, and meteorological
model inputs to determine if the modeled violations in unmonitored
areas appear to be credible. If potential violations are found to be
credible, additional steps may include imposition of enforceable
emissions reductions at nearby emission sources or a commitment to
deploy special purpose monitors and/or saturation monitors in the area
(in order to further evaluate the problem). The state would be required
to document the assessment, including analyses of emissions,
meteorological inputs and ambient data and/or make a commitment to
establish special purpose monitors as part of the attainment
demonstration. Special purpose ambient air monitoring data that is
collected after the attainment demonstration is submitted should be
summarized for use in the area's 5-year monitoring assessment and,
where appropriate, annual monitoring network plans.\123\ Additionally,
monitoring data that is collected as a result of the unmonitored area
analysis assessment (after the attainment demonstration is submitted)
must be reported as a quantitative milestone required under section
189(c)(1) (see Section IV.G of this preamble).
---------------------------------------------------------------------------

    \123\ All states are required to have an annual monitoring plan
(see Section II of this preamble) which meets the siting criteria
for PM2.5 monitors (40 CFR 58.10).
---------------------------------------------------------------------------

    In summary, Option 3 would clarify that an unmonitored area
analysis would be required in all attainment demonstrations, and an
assessment of the unmonitored area analysis results would be required
as part of the attainment demonstration documentation. In contrast to
Option 2, however, the unmonitored area analysis results would not be
used as part of the specific analytical approach for determining
whether a particular control strategy will result in the area attaining
the NAAQS.
    Finally, proposed Option 4 would require states to show attainment
at all current and recent monitoring locations. States would not be
required to provide an unmonitored area analysis as part of the
attainment demonstration. However, the EPA would encourage states to
use information available to them to consider what, if any, impacts may
be occurring in unmonitored areas. States could consider information
such as modeling data, emissions inventories or non-FEM monitoring data
(such as from special purpose monitors or saturation monitoring
studies) which may indicate potential high PM2.5
concentrations in areas that are currently unmonitored. Under this
approach, states could consider model results to develop an assessment
of the likelihood of violations in unmonitored areas. This proposed
option differs from Option 3 in that it would not require an
unmonitored area analysis. Rather, under proposed Option 4, an
unmonitored area analysis would be recommended where the state and/or
the EPA has reason to believe that potential violations may be
occurring in unmonitored areas, or other available information
indicates that further analysis is warranted. States would be expected
to consult with the appropriate EPA Regional Office to evaluate
available information to determine if an unmonitored area analysis is
needed for a particular area.
    The four options presented above would lead to a range of potential
analysis costs by requiring attainment demonstrations at more locations
and with varying degrees of specificity. To the extent that these
analyses reveal additional locations with potential violations, the
effort needed to address these violations could also be higher, and may
ultimately lead to additional reductions, with their associated costs
and benefits. In terms of analysis costs, Option 1 would be expected to
be the least costly option, whereas Option 2 would be expected to be
the most resource intensive. Option 3 is similar to Option 2, except
that if a potential violation is indicated in an unmonitored area,
there would not be a regulatory requirement for the air agency to
identify enforceable controls to eliminate the potential violation. For
example, the air agency could instead elect to site a new monitor to
further characterize air quality in the area. The analysis costs
associated with Option 3 would thus be similar to Option 2.
    Option 4 most closely describes the current policy for the
PM2.5 NAAQS implementation program. Currently, the EPA
recommends that air agencies conduct an unmonitored area analysis, but
there is no regulatory requirement for the air agency to either perform
an unmonitored area analysis or to impose control requirements if the
analysis indicates potential violations. Thus, under Option 4, if an
unmonitored area analysis is performed, the analysis costs associated
with this option would be the same as for Options 2 and 3. Under Option
4, if it is determined by the EPA and the air agency to be unnecessary
to perform an unmonitored area analysis, there would be no additional
analysis costs beyond the monitor-only approach of Option 1. Regarding
the costs and benefits of reductions resulting from additional efforts
to address unmonitored locations (i.e., to the extent that efforts
necessary to address monitored locations do not also address
unmonitored locations), the EPA does not have enough information to
determine the extent of such areas or the measures that would be needed
to address them, nor can the agency predict the extent to which such
measures would be adopted under one option but not another.
    The EPA's four proposed options reflect various combinations with
respect to whether such an analysis is required and the purposes for
which the state and the EPA might use the results of the analysis. The
EPA requests comment on whether an unmonitored area analysis should be
a required component of an attainment demonstration for a
PM2.5 nonattainment area and, if required, how the results
of an unmonitored area analysis should be used. The EPA also requests
comment on the potential costs and benefits of each of the four
specific options, and on which of the options the commenter believes
should be included in the final rule and why.
8. What future year(s) should states model in attainment
demonstrations?
    A state performing a modeling analysis for an attainment
demonstration or impracticability analysis must select a future year
for the analysis. For an attainment demonstration, a state should
select the future modeling year such that all control measures relied
on for attainment will have been fully implemented by the beginning of
that year. To demonstrate attainment, the modeling results for the
nonattainment area must predict that emissions controls implemented no
later than the beginning of the last calendar year preceding the
attainment date will

result in PM2.5 concentrations that meet the level of the
standard.\124\
---------------------------------------------------------------------------

    \124\ Note that for purposes of the PM2.5 NAAQS, a
determination of attainment (or failure to attain), which the EPA is
required to make after the attainment date has passed, is based on
an average of the most recent 3 years of ambient data prior to the
area's attainment date.
---------------------------------------------------------------------------

    While states should choose the future modeling year based on a
number of factors, the EPA recommends the last possible year permitted
under the statute as a starting point for modeling. There are several
reasons for this. First, states with Moderate areas that submit an
impracticability demonstration must show that the area cannot attain
the NAAQS by the end of the sixth calendar year following designation
of the area. Therefore, the appropriate future modeling year for such a
demonstration is the sixth calendar year after designation. Even if a
state does not submit (or does not intend to submit) an
impracticability demonstration, modeling the sixth calendar year is a
logical starting point to determine if attainment by that year is
likely. Second, even though attainment is determined based on 3 years
of ambient data, states do not have to model 2 years before the
attainment date to show modeled attainment. Since the design value is
an average of the annual or 98th percentile value for 3 consecutive
years of data, attainment can still be shown even if concentrations
exceed the NAAQS in one or more of the 3 years used to determine
attainment (as long as the average of the three annual values is below
the level of the NAAQS). Therefore, it can be appropriate to model any
of the 3 years used to determine attainment. Third, if ambient data
show attainment level concentrations in the final statutory attainment
year, a state may be eligible for up to two 1-year extensions of the
attainment date, if the area meets the criteria for such extensions
under CAA section 188(d). Therefore, modeling attainment level
concentrations for the last year permitted by statute is acceptable.
    For all of the reasons stated above, it is both acceptable, and
will in fact be most efficient, for a state to begin the attainment
demonstration process by modeling the last year permitted under the
statute to determine future year modeled PM2.5
concentrations in the sixth year after designations. Thus, in the
attainment demonstrations for areas designated nonattainment in the
first round of designations for the 2012 PM2.5 NAAQS, it
would be appropriate for states to model air quality for 2021.
    Because an area must attain ``as expeditiously as practicable''
according to the CAA, additional considerations are necessary before an
attainment date can be established for a Moderate PM2.5
nonattainment area. For purposes of determining the attainment date
that is as expeditious as practicable, the state must conduct future
year modeling which takes into account expected growth and known
controls. For example, for a Moderate nonattainment area for the 2012
PM2.5 NAAQS, a future base case scenario for the year 2021
(6 years after designations) would project future air quality given
implementation of existing federal, state and local measures. If this
base case scenario demonstrates attainment, then the state must
demonstrate whether attainment could be achieved in an earlier year.
Therefore, the state needs to conduct an analysis to determine if,
collectively, all technologically and economically feasible measures
identified by the state for which the state can initiate implementation
by the beginning of the sixth calendar year following designations, can
advance the attainment date by at least 1 year. Results of this
analysis may indicate attainment can be achieved earlier, through
implementation of all reasonable control measures (i.e., RACM and RACT
and additional reasonable measures).
    If the future base case scenario does not demonstrate attainment,
then a control case scenario is needed to examine whether the
implementation of all technnologically and economically feasible
measures identified by the state would result in attainment in 2021
(for purposes of this example based on the 2012 PM2.5
NAAQS). The control case scenario would add to the model potential
control measures (i.e., RACM and RACT and additional reasonable
measures, plus any additional intrastate transport measures or other
measures on sources outside of the nonattainment area that the state
has identified as feasible to implement by the attainment date). This
modeling, along with other relevant information, would inform a
judgment as to whether attainment of the relevant NAAQS is practicable
by the end of the sixth year after designation or earlier. In the case
of areas designated nonattainment for the 2012 PM2.5 NAAQS
in the first round of designations, if the analysis does not
demonstrate attainment by December 31, 2021, then the analysis could
serve as the technical basis for the state to submit a demonstration
that attainment by the latest statutory attainment date for Moderate
areas is impracticable. This demonstration in turn could serve as the
technical basis for the Administrator to reclassify the area to
Serious.\125\
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    \125\ A demonstration that the area cannot practicably attain by
the Moderate area attainment date would not be the only trigger for
a discretionary reclassification to Serious. The Administrator
maintains wide discretion in making such a determination, with an
impracticability demonstration serving as one potential source of
analysis to inform such a determination.
---------------------------------------------------------------------------

    The EPA believes that it is not reasonable to require states to
model each and every calendar year to determine the appropriate
attainment date for a nonattainment area. Developing and modeling
future year inventories is a time-consuming and resource intensive
process. Multiple emissions models are needed in order to generate
year-specific emissions for the various emissions sectors (e.g. mobile,
non-road, non-EGU point and EGU point). In some cases it may be
reasonable to model one additional interim year before the maximum
statutory attainment date.\126\ However, in most cases, the air quality
benefits of an identified set of RACM and RACT and additional
reasonable measures can be estimated through model sensitivity analyses
and the development of transfer factors (factors to relate tons of
emissions reductions in the area to PM2.5 concentration
changes in the area). For example, states can model across-the-board
percentage reductions in direct PM2.5 and/or precursor
emissions (in separate model runs) to determine the impact of emissions
reductions on PM2.5 concentrations in the area. This
modeling can be performed with a single attainment year modeling
platform, which is much less resource intensive than modeling
additional future years. The identified potential emissions reductions
available from RACM and RACT and additional reasonable measures can be
compared to the magnitude of the modeled PM2.5 reductions
from the sensitivity analyses to determine if all such controls will
advance attainment by a year. The EPA strongly recommends that states
discuss the selection of the future year(s) to model with their
respective EPA Regional Office as part of the modeling protocol
development process and before embarking on running the model(s).
---------------------------------------------------------------------------

    \126\ If several future modeling years are available, in some
cases it may be appropriate for states to interpolate
PM2.5 concentrations between years.
---------------------------------------------------------------------------

9. Modeling Analysis of Controls That Have a De Minimis Impact on
Ambient PM2.5 Concentrations
    In Section IV.D of this preamble, the EPA is proposing that if a
state determines that a Moderate nonattainment area can attain the
PM2.5

NAAQS by the statutory attainment date, the state must adopt and
implement as reasonable control measures (i.e., as RACM and RACT and
additional reasonable measures) only those technologically and
economically feasible control measures that are necessary to ensure
that the area will attain the NAAQS as expeditiously as practicable. In
a Moderate PM2.5 nonattainment area that cannot practicably
attain the relevant NAAQS by the statutory attainment date, the EPA
similarly believes that it may not be reasonable in all cases to
require that a state implement all technologically and economically
feasible control measures. The EPA is thus proposing an option under
which the state may evaluate the air quality impact of technologically
and economically feasible control measures to determine if there is a
subset of such measures that collectively will only achieve negligible
reductions in ambient PM2.5 concentrations in the area.
Similar to the EPA's proposed approach, described earlier in this
section, to determine if a set of technologically and economically
feasible control measures can collectively advance the attainment date
by a year for a Moderate nonattainment area for which a state can
demonstrate attainment by the statutory attainment date, the state
would be required under this proposed option (for a Moderate area that
cannot practicably attain the NAAQS by the statutory attainment date)
to use an air quality model to determine the impact on ambient
PM2.5 levels of the set of otherwise ``reasonable'' controls
that it believes will not collectively reduce ambient PM2.5
concentrations in the area. For this analysis, the state would have to
show that the collective set of controls will have little to no effect
on reducing PM2.5 concentrations in the area.
10. Attainment Year Motor Vehicle Emissions Budgets
    The transportation conformity rule requires that attainment plans
establish motor vehicle emissions budgets for the area's attainment
year. Therefore, once an area's attainment date has been established,
the state would establish motor vehicle emissions budgets for direct
PM2.5 and any relevant PM2.5 precursor for the
attainment year.\127\ A motor vehicle emissions budget for the purposes
of a PM2.5 attainment plan is that portion of the total
allowable emissions within the nonattainment area allocated to on-road
sources as defined in the submitted attainment plan.\128\ Such motor
vehicle emissions budgets would be calculated using the latest planning
assumptions and the latest approved motor vehicle emissions model
available at the time that the attainment plan is developed.\129\
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    \127\ For more information on PM2.5 precursor
requirements, see section 93.102(b)(2)(iv) and (v) of the
transportation conformity rule. See also the May 6, 2005, final
transportation conformity rule that addressed requirements for
PM2.5 precursors. (70 FR 24280).
    \128\ A state would also establish motor vehicle emissions
budgets for an area's attainment year. Those budgets would be the
motor vehicle emissions that the SIP establishes as being necessary
to attain the NAAQS.
    \129\ If an area includes re-entrained road dust in the motor
vehicle emissions budget, the latest approved version of AP-42
should be used unless the EPA has approved an alternative model for
the area.
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F. RFP Requirements

1. Statutory Requirements and Existing Guidance
    ``Reasonable further progress'' (RFP) is a concept included in the
CAA under part D, title I to assure that states make steady,
incremental progress toward attaining air quality standards in the
years prior to the attainment date for a nonattainment area, rather
than merely deferring implementation of control measures and therefore
emissions reductions until the date by which the standards are to be
attained. As discussed elsewhere in this preamble, section 172 of the
CAA addresses nonattainment plan provisions in general. Section
172(c)(2) requires attainment plans to provide for RFP, which is
defined in section 171(l) as ``such annual incremental reductions in
emissions of the relevant air pollutant as are required by [part D of
title I] or may reasonably be required by the Administrator for the
purpose of ensuring attainment of the applicable national ambient air
quality standard by the applicable date.'' Section 172(c)(3) requires
the state plan to include ``a comprehensive, accurate, current
inventory of actual emissions from all sources of the relevant
pollutant or pollutants in such area . . .'' Section 172(c)(1) requires
the state plan to include ``all reasonably available control measures
as expeditiously as practicable (including such reductions in emissions
from existing sources in the area as may be obtained through the
adoption, at a minimum, of reasonably available control technology) . .
.''
    In general terms, the EPA interprets that the purpose of requiring
RFP is to ensure that states with nonattainment areas develop
attainment plans that achieve generally linear progress toward
attainment, rather than deferring emissions reductions until the
applicable attainment date for the area. In the context of implementing
the PM2.5 NAAQS, ``generally linear progress'' means that
emissions of direct PM2.5 and PM2.5 precursors
from controlled sources generally decrease year by year such that the
area ultimately attains the relevant NAAQS by the applicable attainment
date. In the Addendum, the EPA provided guidance and identified four
specific situations in which ``linear progress'' in emissions
reductions to meet RFP may be appropriate:
    1. When pollutants are emitted by numerous and diverse sources.
    2. Where the relationship between any individual source and the
overall air quality is not explicitly quantified.
    3. Where a chemical transformation is involved.
    4. Where the emission reductions necessary to attain the standard
are inventory-wide.\130\
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    \130\ Addendum to the General Preamble, 59 FR 41998 (August 16,
1994), at page 42015.
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    For example, a state with an area whose nonattainment problem is
caused primarily by area sources, such as residential wood combustion,
should be able to demonstrate generally linear progress toward
attainment in that area. In such an area, the state might be able to
require the replacement of a specified percentage of the residential
woodstoves on an annual basis for each year to assure RFP on an annual
basis.
    The EPA's guidance in the Addendum also provided examples of
situations in nonattainment areas in which it might be less appropriate
to expect RFP to be linear, including:
    1. Where there are a limited number of sources.
    2. Where the relationships between individual sources and air
quality are relatively well defined.
    3. Where the emission control systems utilized (e.g., at major
point sources) will result in swift and dramatic emission
reductions.\131\
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    \131\ Ibid.
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    In nonattainment areas characterized by any of these circumstances,
the EPA understands that RFP may be better represented as step-wise
progress as controls are implemented and achieve significant reductions
soon thereafter. For example, if an area's nonattainment problem can be
attributed to a few major stationary sources, the EPA's guidance
indicates that ``RFP should be met by `adherence to an ambitious
compliance schedule' which is likely to periodically yield significant
emission reductions.'' 132 133 While the EPA noted

in the Addendum that adherence to such a schedule does not necessarily
mean it would be unreasonable to achieve generally linear progress, the
agency has long interpreted the language of section 171(1) not to
require some specific level of emissions reductions in any given year.
Unlike certain provisions under subpart 2 governing ozone NAAQS
implementation, subpart 4 does not specify a set percentage of
emissions reductions to be achieved over a certain period of time.
Accordingly, the EPA believes that the facts and circumstances of each
specific area will be relevant to whether the emissions reductions meet
the agency's expectations for ``generally linear progress.''
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    \132\ USEPA, Office of Air Quality Planning and Standards,
``Guidance Document for Correction of Part D SIP's for Nonattainment
Areas,'' Research Triangle Park, NC, January 24, 1984, page 25.
    \133\ Addendum to the General Preamble, 59 FR 41998 (August 16,
1994), at page 42015.
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    With respect to implementation schedules, the EPA recommended in
the Addendum that to meet the statutory RFP requirements, attainment
plans must include ``detailed schedules for compliance with emission
regulations in the [nonattainment] areas and accurately indicate the
corresponding annual emission reductions to be realized from each
milestone in the schedule. In reviewing the SIP, the EPA will determine
whether the annual incremental emission reductions to be achieved are
reasonable in light of the statutory objective to ensure timely
attainment of the PM10 NAAQS. Additionally, the EPA believes
that it is appropriate to require early implementation of the most
cost-effective control measures . . . while phasing in the more
expensive control measures.'' \134\
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    \134\ Ibid. at 42016.
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    The EPA believes that these prior interpretations of the Act's
provisions for RFP continue to be appropriate for the PM2.5
NAAQS. Accordingly, the following section describes the EPA's proposal
for requirements to ensure that states meet the statutory provisions
for RFP for Moderate PM2.5 nonattainment areas.
2. General Proposed Approach to RFP
    To satisfy the statutory requirements for RFP at section 172(c)(2),
the EPA proposes that a state must submit an RFP plan as part of its
Moderate area attainment plan submission. The RFP plan must contain
appropriate information to demonstrate that adequate emissions
reductions will be achieved through control measures in the attainment
plan in order to meet the statutory definition of RFP. The plan must
include an implementation schedule for control measures on sources in
the nonattainment area and an analysis that demonstrates when--and
through what control measures--emissions will decline from the
applicable baseline year to the attainment year. As part of the
analysis, the RFP plan must include a projected inventory for sources
in the area for one (or more) interim year(s). The EPA is proposing and
seeking comment on two options for developing an RFP plan, as well as
on related requirements, as described below. See proposed 40 CFR
51.1012. The EPA also notes that quantitative milestones required under
section 189(c) are directly linked to the RFP plan, as interim
quantifiable indicators intended to demonstrate that an area is making
progress toward attaining the PM2.5 NAAQS, and are therefore
related to the implementation schedule of control measures for a
PM2.5 nonattainment area. Quantitative milestones are more
fully discussed in Section IV.G of this preamble.
    a. Proposed Option 1. Under the first option, the EPA proposes that
the RFP analysis for any Moderate PM2.5 nonattainment area
that can demonstrate attainment by the statutory attainment date must
demonstrate either: (i) Generally linear progress toward attainment by
the applicable attainment date through emissions reductions to be
achieved annually between a baseline year and the projected attainment
date for the area; or, (ii) step-wise progress toward attainment by the
applicable attainment date that will be achieved through adherence to
an ambitious compliance schedule that would not necessarily achieve
reductions on an annual basis. In the second case, the state would be
required to submit a clear rationale and supporting information to
explain why generally linear progress during the attainment period is
not reasonable on an annual basis (e.g., due to the nature of the
nonattainment problem and the types of sources contributing to
PM2.5 levels in the area as discussed in Section IV.F.1 of
this preamble). The EPA also proposes to require that RFP analyses need
to show progress in achieving emissions reductions only for direct
PM2.5 and any precursors that are controlled in the
attainment plan for the nonattainment area.
    Note that the two approaches presented in Option 1 for
demonstrating RFP within the nonattainment area are consistent with the
pattern of emissions reductions of many nationally-applicable federal
emissions reduction measures. For example, new emission standards for
mobile sources may achieve reductions in a generally linear manner over
time, as a portion of the existing vehicle fleet is replaced each year
with new vehicles meeting the more stringent standards. On the other
hand, regulations to reduce emissions from certain stationary source
sectors often have a single compliance date by which controls must be
in place, which typically result in a significant drop in emissions
over a relatively short period (i.e., yield step-wise reductions).
    Because the statute does not clearly establish the applicable
baseline year from which to begin calculating annual emissions
reductions for purposes of demonstrating RFP, the EPA is proposing to
require and seeks comment on a requirement that states use the same
year as the base year inventory chosen for the area, as this inventory
will serve as the basis for developing the control strategy necessary
to bring the area into expeditious attainment. Furthermore, in
developing their RFP analyses for specific nonattainment areas, the EPA
expects that states will use the emissions inventories developed for
those areas and air quality modeling they have completed for attainment
planning purposes. This approach is consistent with the EPA's proposed
approach, described later in this section, not to interpret the CAA as
allowing states to take credit for emissions reductions from sources
outside a nonattainment area when developing their plan to meet the
statutory RFP requirements for PM2.5 nonattainment areas.
    For states with Moderate areas that cannot demonstrate attainment
by the statutory Moderate area attainment date, the statutory RFP
requirements still apply. However, the EPA proposes to require that,
for such areas, the state must provide an analysis of the anticipated
emissions reductions associated with implementing the control measures
identified as RACM and RACT and additional reasonable measures for the
area. The EPA notes that even if a state adequately demonstrates that
it cannot attain the NAAQS in a given area by the statutory attainment
date, the CAA still requires the state to submit a Moderate area
attainment plan meeting the requirements for such attainment plans,
including for RFP. An additional RFP analysis will be required as part
of the Serious attainment plan for the area once the EPA reclassifies
it to Serious.
    Similar to the approach taken for RFP in the remanded 2007
PM2.5 Implementation Rule, the EPA is proposing under this
option that all states must follow one primary

approach for conducting the RFP analysis, but that they also have an
option to conduct a secondary analysis that will provide greater
flexibility in setting RFP goals with alternative emissions reductions
and air quality improvement scenarios. The primary approach would be to
benchmark emissions reductions on a pollutant-by-pollutant basis
starting from the pollutant's baseline emissions level. The state would
then be required to calculate reductions in emissions of each pollutant
on an annual basis that would be needed to bring the area into
attainment by the projected attainment date.
    The EPA recognizes that different control measures address
different pollutants, and that states may be able to implement some
measures more quickly than others. Thus, in the optional secondary
analysis, the state could present a different combination of emissions
reductions at similar time intervals that would provide an equivalent
or better result in terms of net air quality improvement. This
``equivalency determination'' would allow states flexibility to address
different pollutants (i.e., direct PM2.5 and
PM2.5 precursors regulated under the control strategy for
the area) according to different schedules so long as the EPA finds the
projected net air quality improvements to be achieved through this
alternative combination of emissions reductions to be equivalent to or
better than those that would be achieved through generally linear
emissions reductions across all pollutants in the area. This proposed
approach recognizes that an important element of establishing
appropriate emissions reductions targets for meeting RFP requirements
for PM2.5 is quantifying the relative degrees of control of
various pollutants.
    As discussed above, the primary approach for ensuring that RFP is
met in a PM2.5 nonattainment area is to require that the
state reduce each pollutant--that is, direct PM2.5 and all
precursors not otherwise eliminated from control requirements--by some
amount on an annual basis. The EPA's primary proposed RFP analysis, an
emissions benchmark analysis, would reflect generally linear progress
(or step-wise progress if more appropriate and adequately justified) to
reduce those pollutants that the state intends to control to attain the
PM2.5 NAAQS by the applicable attainment date. See proposed
40 CFR 51.1012(b). For example, a state that can demonstrate that their
Moderate nonattainment area can attain the 2012 PM2.5 NAAQS
by an attainment date of December 31, 2021 would also need to achieve
emissions levels that represent attainment in 2021. If the attainment
plan requires a 10 percent reduction in NOX emissions and a
14 percent reduction in PM2.5 direct emissions from 2011
levels in order for the area to demonstrate attainment in 2021, then
the RFP benchmark for NOX would reflect roughly a 1 percent
reduction in NOX emissions per year, and the benchmark level
for PM2.5 would be roughly a 1.4 percent reduction per year.
    The EPA proposes that states must provide an implementation
schedule for control measures that would achieve emissions reductions
consistent with those calculated as part of the RFP benchmark analysis.
However, a state could choose to submit an ``equivalency'' analysis in
addition to the RFP benchmark analysis and associated implementation
schedule that presents an alternative combination of pollutant emission
reductions (i.e., alternative implementation schedule for control
measures) that achieves air quality improvements that are equivalent to
or better than the RFP benchmark analysis. In such a case, the state
would need to make an adequate showing that the alternative schedule
for implementing control measures will provide estimated air quality
improvements that are roughly the same as, if not better than, those
that the emissions reductions determined through the RFP benchmark
analysis would provide. If a state elects to follow this approach, it
must provide in its RFP plan the information necessary to assess
whether an alternative schedule of emissions reductions is generally
equivalent, in air quality terms, to the RFP benchmark analysis
reduction levels, such as attainment demonstration modeling results
that link emissions reductions of various precursor emissions with air
quality improvements. Under this proposed approach, the EPA would
require states to use this information to evaluate the equivalence of
alternative combinations of pollutant emissions reductions. The EPA
would recommend that states estimate air quality improvements
associated with intermediate emissions control levels (i.e., air
quality improvement targets) by assuming that the same relationship
between emissions and air quality applies at intermediate levels as
would apply at attainment levels.
    The EPA continues to recognize that because atmospheric processes
are quite complex, a specific percent change in emissions of
PM2.5 precursors does not lead to an equivalent percent
change in air quality, potentially creating uncertainty as to whether
alternate emissions control scenarios will achieve equivalent benefits.
Nevertheless, the EPA believes that it is important to provide the
flexibility to address different pollutants on different timetables so
long as the plan can reasonably be expected to achieve the intended air
quality benefits represented by the RFP benchmark analysis. In general,
the EPA would not expect a state to conduct dispersion modeling
specifically to assess whether an alternative approach to meeting RFP
will provide equivalent air quality benefits as the benchmark approach.
Instead, the attainment plan modeling addresses the nonlinearities at
attainment levels, and the EPA believes for RFP analysis purposes that
the relationship between emissions and air quality at attainment levels
provides an adequate approximation of the relationship at interim RFP
levels.
    b. Proposed Option 2. Under the second option, the EPA proposes a
simplified approach to developing an RFP plan that focuses on the
emissions reductions anticipated from each of the particular control
measures identified by the state as part of the analysis to identify
RACM and RACT and additional reasonable measures for sources in the
nonattainment area. Under this option, the first step in developing the
RFP plan would be for the state to establish the implementation
schedule on a year-by-year basis for all control measures contained in
the control strategy for sources in the area beginning with the date of
designation of the area and ending with the projected attainment date
of the area. The schedule would need to comply with the statutory
requirement that all RACM and RACT must be implemented within the first
4 years following designation, but the state would have discretion
beyond that requirement to schedule the implementation of any other
measures necessary for expeditious attainment. Overall, the
implementation schedule would need to demonstrate that control measures