new control requirements for sources of a particular precursor, but it
would not address the potential impact of increased emissions of the
precursor in the area due to new or modified sources, as is reasonably
needed under the NNSR precursor demonstration. The evaluation of
controls required for expeditious attainment does not consider what
happens if new sources move into an area. Thus, while a state might be
able to show that controlling existing sources of a precursor does not

advance attainment, the analysis would not determine whether a new
major source of that precursor might have a significant contribution to
air quality. The EPA believes it is important for purposes of CAA
section 189(e) and our overall environmental goal under the NNSR
program to evaluate emissions increases. Consequently, the EPA has
revised the details of the specific types of demonstrations to include
a specific stand-alone demonstration for purposes of exempting new
major stationary sources and major modifications of a precursor from
regulation under the NNSR permitting program.

IV. Requirements for PM2.5 Moderate Nonattainment Area Plans

    Sections 189(a), (c), and (e) of the CAA require that Moderate area
attainment plans contain the following: (i) An approved permit program
for construction of new and modified major stationary sources (CAA
section 189(a)(1)(A)); (ii) a demonstration that the plan provides for
attainment by no later than the applicable Moderate area attainment
date or a demonstration that attainment by that date is impracticable
CAA (section 189(a)(1)(B)); (iii) provisions for the implementation of
RACM and RACT no later than 4 years after designation (CAA section
189(a)(1)(C)); (iv) quantitative milestones that will be used to
evaluate compliance with the requirement to demonstrate reasonable
further progress (RFP) (CAA section 189(c)); and, (v) evaluation and
regulation of PM2.5 precursors (in general to meet RACM and
RACT and other attainment planning requirements, and as specifically
provided for major stationary sources under CAA section 189(e)). In
addition, subpart 1 requirements for attainment plans continue to apply
to PM2.5 nonattainment areas unless they are superseded by
subpart 4 provisions and include the following: (i) A description of
the expected annual incremental reductions in emissions that will
demonstrate RFP (CAA section 172(c)(2)); (ii) emissions inventories, as
necessary (CAA section 172(c)(3)); (iii) other control measures
(besides RACM and RACT) needed for attainment (CAA section 172(c)(6));
and, (iv) contingency measures (CAA section 172(c)(9)). The EPA notes
that its longstanding guidance on interpreting these statutory
requirements is embodied in the General Preamble and the Addendum.\54\
The preamble for the proposed rule presented several interpretations of
these provisions, and further explained where its proposal varies from
past EPA guidance and the reasons for the variance. The following
sections of this preamble explain the EPA's final approach and, where
different from the proposal, also explain EPA's reasons for finalizing
an amended approach. This final rule reflects our careful consideration
of the numerous thoughtful comments we received from air agencies, who
are responsible under the CAA for these implementation activities, and
a variety of other stakeholders.
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    \54\ See 57 FR 13498, 13536, 13537, 13538, 13539, 13540, 13541,
13542, 13543, 13544 and 13545 (April 16, 1992); and 59 FR 41988
(August 16, 1994).
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A. Plan Due Dates

1. Summary of Proposal
    The EPA proposed to require that all Moderate area plan elements
for a nonattainment area be submitted by the state no later than 18
months from the effective date of designation. The attainment plan
submission would thus include all necessary plan elements required
under CAA subparts 1 and 4.
2. Final Rule
    The final regulations at 51.1003(a) require all Moderate
nonattainment area elements to be submitted by no later than 18 months
from the date of designation, as proposed. Section 189 of the CAA
specifies the schedule by which states must submit attainment plans for
the PM2.5 NAAQS. Specifically, CAA section 189(a)(2)(B)
requires states to submit an attainment plan that meets Moderate area
attainment plan requirements no later than 18 months from the date of
nonattainment designation.\55\ While subpart 1 of the CAA could
potentially be interpreted to authorize the EPA to provide up to 3
years after designation for states to submit certain attainment plan
elements, the EPA believes that such an interpretation would be
inconsistent with the specific deadlines that Congress imposed in
subpart 4. The EPA concludes that all subpart 1 and subpart 4
nonattainment area requirements should be considered together in order
to facilitate state development, and EPA review, of a comprehensive
plan to attain the PM2.5 NAAQS in a given nonattainment
area. In fact, the EPA finds that meeting key subpart 1 requirements
within the 18-month timeframe of subpart 4 is fundamentally necessary
for the state to develop an approvable plan. For example, the state
must develop an emissions inventory (or inventories) either before or
at the same time as the other attainment plan elements due under
subpart 4 because the information contained in the emissions inventory
is critical for development of other elements of the Moderate area
attainment plan, such as its precursor analysis, analysis of RACM and
RACT and additional reasonable measures, and attainment demonstration
modeling. The EPA's ability to evaluate the submitted attainment plan
therefore will be impaired if the state does not submit all the
required plan elements at the same time.
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    \55\ The EPA notes that Congress provided different statutory
deadlines for submission of attainment plans under subpart 1 and
subpart 4. Under section 172(b) of the CAA, the EPA is directed to
establish the date for the attainment plan submission, but it can
extend no later than 3 years from the date of a nonattainment
designation. By contrast, under CAA section 189(a)(2)(B), the
statute provides that states must make the attainment plan
submissions within 18 months after designation. Due to the December
2013 court decision in NRDC v. EPA, however, the EPA promulgated an
alternative submission date of December 31, 2014, for attainment
plans for the 1997 PM2.5 and 2006 PM2.5 NAAQS
in order to provide a reasonable, prospective due date for
attainment plans that must comply with subpart 4 requirements and to
clarify the requirements that a state must meet prior to
redesignation of a PM2.5 nonattainment area. See 79 FR
31566 (June 2, 2014).
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3. Comments and Responses
    Comment: Commenters suggested that the EPA should interpret the
statute to allow more time for states to develop and submit contingency
measures.
    Response: As discussed earlier in this section, the EPA believes
that it would be inconsistent with the specific deadlines that Congress
imposed in subpart 4 to allow contingency measures to be submitted
later than the other elements of the attainment plan. Contingency
measures need to be adopted and ready for rapid and timely
implementation in the event a nonattainment area fails to meet RFP
requirements or fails to attain the PM2.5 NAAQS by the
applicable attainment date. The state's evaluation of what emissions
controls are appropriate to meet the contingency measure requirement is
closely related to other aspects of the attainment plan, such as the
pollutants and sources to be addressed in meeting the RACM/RACT
requirements, and the amount of emissions reductions that the
contingency measures should achieve, based upon the facts and
circumstances of the attainment plan for the area. The same types of
facts and analyses that are necessary for the other elements of an
attainment plan are directly relevant to the development of contingency
measures.
    Although nothing in the CAA prohibits states from making separate
attainment plan submissions to meet the

individual required elements for attainment plans in advance of the
required date, the EPA presumes that development and submission of all
of the attainment plan elements simultaneously will be most efficient,
both for the state and for the EPA in reviewing the state's submission.
A Moderate area implementation plan with a single SIP submission due
date will be less administratively burdensome than a program with two
SIP submission due dates. Under an approach with two submissions, the
state would likely need to issue two sets of proposed regulations, hold
two sets of public hearings, and respond to two sets of public
comments, rather than dealing with all of these requirements in one
comprehensive action. Likewise, the EPA would have two separate
submissions to review and two sets of proposed and final actions to
publish in the Federal Register for every Moderate nonattainment area.
Thus, for the reasons outlined earlier, the final rule includes a
single Moderate area attainment plan submission deadline of 18 months
after designation. Accordingly, the areas designated as nonattainment
for the 2012 PM2.5 NAAQS (with an effective date of April
15, 2015) are required to submit Moderate area attainment plans to the
EPA no later than October 15, 2016. See 40 CFR 51.1003(a).

B. Emissions Inventory Requirements

1. Summary of Proposal
    In the proposal, the EPA proposed for both Moderate and Serious
areas to require both a ``base year inventory for the nonattainment
area'' and an ``attainment projected inventory for the nonattainment
area.'' The proposal spelled out a list of requirements for each of
these inventories. The proposal also specified, based on the timing
requirements of CAA section 172(b), that the emissions inventories
required for a Moderate area must be submitted within 18 months after
the effective date of the designation of the nonattainment area.
    The EPA proposed that the base year inventory for the nonattainment
area: (a) Be required to represent one of the 3 years used for
designations or another technically appropriate year; (b) include
actual emissions of all sources within the nonattainment area; (c) be
annual total or average-season-day emissions in accordance with the
NAAQS violation(s) (annual and/or 24-hour); (d) include direct
PM2.5 (filterable and condensable) as well as all scientific
PM2.5 precursors; (e) follow the Air Emissions Reporting
Requirements (AERR), 40 CFR part 51, subpart A for the emissions
thresholds for point sources; (f) use the level of detail as prescribed
by the AERR; and (g) still meet the public review requirements even if
submitted as a separate plan.
    The EPA further proposed that the attainment projected inventory
for the nonattainment area (a) be required to represent projected
emissions in the first year for which attainment is demonstrated by the
modeled attainment demonstration; (b) include projected emissions of
the same sources included in the base year inventory for the
nonattainment area; (c) use the same temporal period as the base year
inventory (annual or average-season-day); (d) include the same
pollutants as the base year inventory; (e) report as point sources the
same sources treated as point sources in the base year inventory; (f)
be consistent in inventory detail with the base year inventory; and (g)
still meet the public review requirements even if submitted as a
separate plan.
2. Final Rule
    The final regulations at 51.1008 provide the inventory requirements
for Moderate areas. The EPA received a number of comments on the
emissions inventory requirements for Moderate areas. Commenters both
supported the provisions of the proposed rule and objected to some
aspects of the inventory requirements. The EPA is finalizing all of the
proposed Moderate area requirements with some modifications based on
comments. Specifically, the definition of what can constitute a
seasonal inventory has been made more flexible to accommodate certain
cases, as explained in Section IV.B.2.c of this preamble.
    Pursuant to its authority under section 110 of title I of the CAA,
the EPA has long required states to submit inventories of the emissions
of criteria pollutants and their precursors. The EPA codified these
requirements in 40 CFR part 51, subpart Q in 1979 and amended them in
1987. Additionally, the 1990 CAA Amendments revised many of the
provisions of the CAA related to attainment of the NAAQS and the
protection of visibility in mandatory Class I federal areas (certain
national parks and wilderness areas). These revisions established new
emissions inventory requirements applicable to areas that were
designated nonattainment for certain pollutants. In the case of PM,
Congress did not create a specific emissions inventory requirement in
subpart 4 that would supersede the emissions inventory requirement
under subpart 1. Thus, the CAA section 172 (c)(3) emissions inventory
requirements continue to apply, and that provision explicitly requires
``a comprehensive, accurate, and current inventory of actual emissions
of the relevant pollutants'' in the nonattainment area. In addition,
the specific attainment plan requirements for the PM2.5
NAAQS set forth in CAA section 189(a) and associated modeling
requirements make an accurate and up-to-date emissions inventory a
critical element of any viable attainment plan. Because of the nature
of PM2.5, the EPA concludes that the statutory requirements
for emissions inventories need further elaboration through additional
regulatory requirements as described later.
    Emissions inventory data serve as the foundation for various types
of analyses performed by states and by the EPA. For example, these data
enable states to evaluate the degree to which different emissions
sources contribute to the nonattainment problem in a given
nonattainment area and enable states to estimate the air quality
improvement that can be achieved through different control measures.
States should use the best available, current emissions inventory
information for attainment plan development, because high quality
emissions inventory data are essential for the development of an
effective control strategy. To assist states in preparing complete,
high quality inventories, the EPA provides guidance for developing
emissions inventories called ``Emissions Inventory Guidance for
Implementation of Ozone and Particulate Matter National Ambient Air
Quality Standards (NAAQS) and Regional Haze,'' which is available from
https://www.epa.gov/air-emissions-inventories/emissions-inventory-guidance-documents. This guidance is commonly called the ``SIP
Emissions Inventory Guidance.'' The EPA recommends that states consult
this guidance while developing the emissions inventories to meet
statutory and regulatory requirements.
    a. Inventory Requirements. As explained in the proposed rule, CAA
section 172(c)(3) requires states to submit an emissions inventory and
periodic revisions thereof with an attainment plan. 80 FR at 15363. In
addition, pursuant to CAA section 301, the EPA has authority to
promulgate regulations as necessary for the implementation of the
PM2.5 NAAQS, including requirements pertaining to emissions
inventories. In this final action, the EPA is establishing several
different inventory requirements that the agency has determined are
necessary

for the proper implementation of the PM2.5 NAAQS in
attainment plans.
    There are three key facets of the emissions inventory requirements,
as described later: (i) The type of inventories required; (ii) the
timing of submission of these inventories; and (iii) the content of
these inventories. These content requirements are described in this
section; however, the EPA's rationale for these content requirements is
in some cases further described in subsequent sections of this
document.
    First, states must submit at least two separate and distinct
nonattainment area emissions inventories as elements of an attainment
plan. The first emissions inventory is relevant for assessing the
current or base year emissions from sources located in the
nonattainment area; the second emissions inventory is a projected
inventory relevant for assessing emissions in the target attainment
year in the nonattainment area. The first type of inventory is called
the ``base year inventory for the nonattainment area,'' and the second
type of inventory is called the ``attainment projected inventory for
the nonattainment area.'' See 40 CFR 51.1000. The base year inventory
for the nonattainment area is necessary for development and evaluation
of various elements of the attainment plan, such as the determination
of appropriate pollutants, sources, and emission controls addressed in
other elements of the attainment plan for the nonattainment area. The
attainment projected inventory is necessary to implement the attainment
demonstration requirement of CAA section 189(a)(1)(B), and it also may
be used as part of meeting the RFP requirement (see Section IV.F of
this preamble). The need for the attainment projected inventory also
stems from the need for both the EPA and the public to be able to
compare, during their reviews of the attainment plan, the base year
inventory against the attainment projected inventory for the
nonattainment area. For these reasons, this rule establishes a
regulatory requirement at 51.1008 that Moderate area attainment plans
must include a base year inventory for the nonattainment area and an
attainment projected inventory for the nonattainment area.
    Second, as noted in Section IV.A of this preamble, to meet the
statutory requirements for submission of certain attainment plan
elements required under subpart 4, the EPA believes that states must
meet the same submission schedule for emissions inventories as for the
other elements of an attainment plan, i.e., within 18 months after the
effective date of the designation of the nonattainment area. This
schedule must apply to both of these emissions inventories because they
are necessary for effective evaluation of the attainment plan as a
whole. Consequently, under the authority of CAA section 172(b), this
rule establishes a regulatory requirement for Moderate areas that
states must submit the required base and projected emissions
inventories by 18 months after designation.
    Third, the EPA is establishing specific requirements for both the
base year inventory for the nonattainment area and for the attainment
projected inventory for the nonattainment area in order to implement
the PM2.5 NAAQS most effectively. Accordingly, this final
rule requires that the base year inventory for Moderate nonattainment
areas must meet the following minimum criteria 1 through 7:
    (1) The inventory year must be one of the 3 years used for
designations for the relevant PM2.5 NAAQS or another
technically appropriate inventory year. Another inventory year may be
chosen under specific circumstances (e.g., to account for a change in
sources in the nonattainment area, changes in nonattainment area
boundaries, to allow the base year to be consistent with the base year
needed for the conformity rule, or significant time lag between
designations and preparation of the inventory) with consultation from
the appropriate EPA Regional Office. This requirement is intended to
ensure that the inventory will adequately represent the emissions
sources that contributed to the nonattainment designation for the area.
See 40 CFR 51.1008(a)(1)(i).
    (2) The inventory must include actual emissions of all sources
within the nonattainment area. This requirement stems directly from the
language in CAA section 172(c)(3). Sources outside of the nonattainment
area are explicitly not included in the section 172(c)(3) requirement
with the words ``in such area.'' Furthermore, the EPA interprets the
Act requirement for ``actual emissions from all sources'' in CAA
section 172(c)(3) as intending to include all emissions that may
contribute to the formation of PM2.5 within the
nonattainment area. This means that the inventory must include point
sources, stationary nonpoint sources,\56\ mobile sources, prescribed
fires and wildfires. The EPA encourages states and tribes to work
together to ensure that the information used in developing the base
year inventory for the nonattainment area is inclusive of all emissions
from the designated nonattainment area, including emissions from
sources in tribal areas located therein. See 40 CFR 51.1008(a)(1)(ii).
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    \56\ Point sources are the same as major stationary sources, and
the term indicates sources that must be reported at an individual
facility with process-level details. Nonpoint sources are all other
stationary sources, and the term indicates sources that are reported
as a county total. The definitions for this rule (see 51.1000) refer
to the definitions in the AERR (40 CFR part 51, subpart A). Nonpoint
sources include minor sources, synthetic minor sources, and area
sources such as residential heating and other sources where it is
not realistic to estimate emissions from each emissions point.
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    (3) The emissions must be reported as annual total emissions,
average-season-day emissions, or both, as appropriate for the relevant
PM2.5 NAAQS. The rationale for the type(s) of emissions
provided must be included as part of the attainment plan. When seasonal
emissions are included, the rationale for the seasonal period must also
be included as part of the attainment plan. A discussion of the EPA's
rationale for including the option of seasonal or annual inventories is
provided in Section IV.B.2.c of this preamble. See 40 CFR
51.1008(a)(1)(iii).
    (4) As discussed earlier and consistent with past implementation
rule requirements, the inventory must include emissions of direct
PM2.5 (both filterable PM2.5 and condensable
PM2.5, provided as separate components), as well as all
scientific PM2.5 precursors (SO2, NOX,
VOC and ammonia). A discussion of the EPA's rationale for including
this requirement is provided in Section IV.B.2.d of this preamble. See
40 CFR 51.1008(a)(1)(iv).
    (5) States must follow the Air Emissions Reporting Requirements
(AERR), 40 CFR part 51, subpart A criteria for emissions thresholds for
states to use to determine which emissions sources must be reported as
point sources. This requirement is consistent with past implementation
rules and is needed to specify whether emissions must be submitted as
specific major source stationary facilities with detailed emissions
processes or whether emissions can be provided as county totals (i.e.,
area sources, also called nonpoint sources). A discussion of the use of
40 CFR part 51, subpart A for the emissions thresholds is provided in
Section IV.B.2.e of this preamble. See 40 CFR 51.1008(a)(1)(v).
    (6) The level of detail of the emissions included in the inventory
must be consistent with the detail required by 40 CFR part 51, subpart
A. For example, all emissions must be subdivided to individual
emissions processes within a facility or county. While these details
should underlie the emissions

inventory, this information can be summarized for other elements of the
attainment plan. This requirement is consistent with the remanded 2007
PM2.5 Implementation Rule and is needed to define the data
reporting elements (i.e., how they are reported) as opposed to the
emissions values (i.e., how much emissions derive from each source or
source category) of the emissions inventories submitted to the EPA. See
40 CFR 51.1008(a)(1)(vi).
    (7) If the base year inventory for the nonattainment area is
submitted to the EPA as a separate plan submission (i.e., severed from
the overall attainment plan and provided separately), the inventory
must still meet the notice and public hearing requirements of CAA
sections 110(a)(1) and 110(a)(2).
    For the attainment projected inventory for Moderate nonattainment
areas, this final rule also establishes specific requirements necessary
to implement the PM2.5 NAAQS effectively. Accordingly, the
attainment projected inventory must meet the following minimum criteria
1 through 7:
    (1) The year of the projected inventory must be the most
expeditious year for which projected emissions show modeled
PM2.5 concentrations below the level of the NAAQS,
consistent with the requirement for expeditious attainment by no later
than the applicable deadlines provided in the statute. See 40 CFR
51.1008(a)(2)(i).
    (2) The emissions must be projected emissions from the same sources
included in the base year inventory for the nonattainment area and any
new sources projected to locate within the boundaries of the
nonattainment area. The projected emissions should be the best
available representation of expected emissions, and thus should take
into account emissions growth and contraction, facility closures, new
facilities, new controls and other changes in emissions forecast to
occur between the base year and the attainment year. In deciding what
factors are relevant, states should consider factors affecting
projected emissions that could significantly alter the conclusions of
the modeled attainment demonstration. See 40 CFR 51.1008(a)(2)(ii). For
prescribed and wildfire emissions, Section IV.D.3.b of this preamble
describes in more detail the appropriate way to handle these sources in
the attainment projected inventory.
    (3) The temporal period of emissions must be the same temporal
period (annual, average-season-day, or both) as the base year inventory
for the nonattainment area. See 40 CFR 51.1008(a)(2)(iii).
    (4) Consistent with the base year inventory for the nonattainment
area, the inventory must include all emissions of direct
PM2.5 (both filterable and condensable PM2.5
provided as separate components), as well as all emissions of the
scientific precursors (SO2, NOX, VOC and
ammonia). See 40 CFR 51.1008(a)(2)(iv).
    (5) The same sources reported as point sources in the base year
inventory for the nonattainment area must also be provided as point
sources in the attainment projected inventory for the nonattainment
area. Likewise, nonpoint and mobile source projected emissions must
also be provided using the same delineations as the base year
inventory. See 40 CFR 51.1008(a)(2)(v).
    (6) The detail of the emissions included must be consistent with
the level of detail in the base year inventory (i.e., as required by 40
CFR part 41, subpart A). See 40 CFR 51.1008(a)(2)(vi).
    (7) If the attainment projected inventory for the nonattainment
area is submitted to the EPA as a separate plan submission (e.g.,
severed from the overall attainment plan and provided separately), then
the inventory must still meet all the notice and public hearing
requirements of CAA sections 110(a)(1) and 110(a)(2).
    b. Comparison to Inventory Requirements from Earlier
PM2.5 Implementation Rules. The 2007 PM2.5
Implementation Rule required states to submit specific emissions
inventories in connection with the RFP requirements of CAA section
172(c)(2) under subpart 1. In this rule, no specific RFP related
inventory is required, but the attainment projected inventory for the
nonattainment area also may serve a purpose for evaluation of RFP. Past
EPA guidance with respect to RFP requirements under subpart 4 has not
explicitly required a separate emissions inventory for this purpose for
PM10 NAAQS. Through evaluation of the RFP requirement in
connection with this rulemaking, however, EPA has determined that there
may be circumstances in which such an approach may be appropriate. For
this reason, the EPA describes this issue more fully in Section IV.F of
this preamble.
    The 2007 PM2.5 Implementation Rule also required states
to submit a statewide base year emissions inventory as part of the
attainment plan. The EPA included the statewide emissions inventory
requirement because it was relevant to evaluation of emissions
reductions from sources outside of the designated nonattainment area
for purposes of RFP. The EPA no longer interprets the CAA to allow such
reductions for purposes of RFP, so this particular form of emissions
inventory is not needed for attainment plan for the PM2.5
NAAQS. Furthermore, statewide inventories are already required as part
of the AERR (40 CFR part 51, subpart A) on a triennial basis. While
these inventories do not receive the same level of scrutiny as
inventories associated with attainment plans, the EPA believes that
this existing statewide inventory requirement is sufficient for
understanding the PM2.5 nonattainment contributions from
areas outside of the nonattainment area, which is a necessary component
of modeled attainment demonstrations described in Section IV.E of this
preamble.
    c. Seasonal Inventories. The statute does not explicitly address
whether the emissions inventory required under CAA section 172(c)(3)
should include emissions throughout an entire calendar year or
emissions during some shorter portion of the year that may be
appropriate for implementation of a particular NAAQS. In the case of
the PM2.5 NAAQS, the standards currently include both annual
NAAQS and 24-hour NAAQS. With respect to the annual NAAQS, the form of
the NAAQS includes monitored ambient PM2.5 values at all
times throughout the course of the year, and thus an annual emissions
inventory is necessarily required for development of an appropriate
attainment plan for a given area. In the case of the 24-hour NAAQS,
however, the form of the NAAQS is based upon monitored values on
particular days with high levels of ambient PM2.5, and in
some nonattainment areas those days may occur only during a distinct
and definable season of the year. The EPA considers it appropriate to
interpret the emissions inventory requirements of the CAA in light of
the specific inventory needs that are relevant for the NAAQS in
question. For the PM2.5 NAAQS, states can meet the inventory
requirement with different combinations of temporal resolutions for the
emissions. For the annual standard, annual emissions must be submitted.
For the 24-hour standard, states must submit either an annual or an
average-season-day inventory and optionally may submit both. For a
nonattainment area for both the annual and 24-hour standard, states can
meet the inventory requirement with only an annual inventory or with
both an annual and average-season-day inventory.
    In contrast with the annual PM2.5 NAAQS, the 24-hour
PM2.5 NAAQS are designed to protect against peak exposures.
Thus, for the 24-hour PM2.5

NAAQS, there are circumstances in which the EPA believes that only
seasonal emissions inventories may be useful for attainment planning
purposes. This rule at 40 CFR 51.1008(a)(1)(iii) allows states to use
seasonal inventories for attainment plan development for attaining the
24-hour PM2.5 standard in areas that are designated
nonattainment for only the 24-hour standard. Use of a seasonal
emissions inventory will also be appropriate only if the monitored
violations of the 24-hour PM2.5 NAAQS in the area occur
during an identifiable season. In the event that it is appropriate to
rely on a seasonal emissions inventory, the state should confer with
the EPA concerning the exact length of the season and the start and
stop dates of the season. The duration and start and stop dates of the
season will be an important component of the attainment plan and must
be approved by the EPA along with other elements of the attainment plan
for a given nonattainment area. Further, this rule requires that
seasonal inventories must use average-season-day emissions values for
this purpose, defined by 40 CFR 51.1000. The nature of some seasonal
PM2.5 emissions sources (e.g., residential wood combustion)
does not allow for only weekday emissions to be included in the
inventory, therefore all days must be included. The state would need to
explain the rationale for the duration of the season used for the
inventory as part of the attainment plan submission. To justify the use
of a seasonal emissions inventory, the state must demonstrate why a
seasonal emissions inventory is appropriate for the particular
PM2.5 nonattainment area in question.
    Commenters recommended that the EPA should allow episode-specific
inventories, in lieu of seasonal inventories. As a result, the EPA
acknowledges in this final rule that, for some source categories, it
may be advisable to limit the ``season'' considered in calculating
emissions to an episodic period to reflect periods of higher emissions
during periods of high ambient PM2.5. Such an approach could
help to ensure the nonattainment area inventory reflects the emissions
conditions that led to an initial nonattainment area designation. For
example, if nonattainment conditions are associated only with periods
of peak emissions from residential wood combustion, then an episodic
average for residential wood combustion may be more appropriate than a
seasonal average. The resulting seasonal emissions inventory would then
have a mix of the seasonal averages as defined by 40 CFR 51.1000 for
most categories, but using a shorter period for the emissions
categories that can be justified and an improvement. In such cases, in
addition to the requirement to justify the seasonal period, the state
must additionally justify the factual basis for the period used to
calculate emissions from such categories, and this would be subject to
EPA approval. While the EPA encourages using the same averaging period
for all sectors for purposes of simplicity, an episodic averaging
period may only be needed for a select group of sources or even for a
single category of sources. Those special cases must be explained in
the emissions inventory part of the state implementation plan [see 40
CFR 51.1008(a)(1)(iii)]. For the purposes of the definitions included
in this final rule, all non-annual emissions (whether seasonal or
episodic) will be referred to as ``seasonal'' in this rule.
    d. Pollutant Requirements. This rule requires that states must
submit emissions inventories that include all emissions of direct
PM2.5 and all emissions of scientific PM2.5
precursors: SO2, NOX, VOC and ammonia.
Furthermore, the inventories must differentiate between the condensable
and filterable portions of direct PM2.5 emissions, and
states must provide this information in the emissions inventories as
separate components. As described in Section IV.B.3 of this preamble,
commenters disagreed with the EPA's proposal to require inclusion of
ammonia emissions and to require separate reporting of condensable and
filterable emissions. The approach being finalized in this rule does
not differ from the EPA's proposal despite these adverse comments.
    Section II.B of this preamble describes the background needed to
understand the importance of including these precursors in emissions
inventories for attainment plan purposes for the PM2.5
NAAQS. Emissions information about PM2.5 and its precursors
is a necessary precondition to meeting other core attainment plan
requirements, such as effective evaluation of control measures and
adequate demonstration of projected future attainment of the NAAQS
through modeling. The EPA notes that, with respect to requiring states
to include emissions of direct PM2.5 and PM2.5
precursors in emissions inventories, the agency is following the
requirements it established for the 2007 PM2.5 NAAQS
Implementation Rule in the past.\57\ Section 172(c)(3) of the CAA
explicitly requires states to submit a ``comprehensive, accurate,
current inventory of actual emissions of the relevant pollutants'' and
the EPA continues to believe that to meet these basic statutory
requirements for the PM2.5 NAAQS, states must address
PM2.5 and all PM2.5 precursors in their emissions
inventories.
---------------------------------------------------------------------------

    \57\ 72 FR 20647 (April 25, 2007).
---------------------------------------------------------------------------

    The EPA requires states to use the best available methodologies for
estimating emissions of PM2.5 and its precursors.
    e. The AERR Defines the Thresholds, Data Elements and Data Methods.
Because the provisions of the CAA do not specify the form of the
emissions information to be reported to the EPA for meeting the
attainment plan inventory requirement under CAA section 172(c)(3), it
is necessary for the EPA to prescribe specifically the data elements of
that emissions inventory and the attainment projected inventory. The
EPA uses the AERR to define basic requirements/parameters of reporting
emissions for all pollutants. This approach creates consistency and
eases the burden for the states, because states have one basic set of
rules that apply to all emissions they have to report to the EPA.
    Distinct from the emissions values (i.e., how much emissions derive
from each source or source category), the emissions elements (i.e., how
they are reported) refer to the reporting definitions, data codes and
required data fields. Under this final rule, states must use the
emissions elements from 40 CFR part 51, subpart A in preparing their
inventories to be submitted to the EPA for implementing the
PM2.5 NAAQS. It also requires that states use point source
thresholds from Appendix A of the same subpart. This is consistent with
past requirements for the form of emissions inventories.
    In addition to defining the point source thresholds and data
elements, 40 CFR part 51, subpart A also requires states to submit
emissions information to the EPA. The EPA is not referring to those
emissions submission requirements here, but rather to the emissions
elements--the definitions, data codes and required data fields. Later,
the EPA addresses the issue of whether the emissions values submitted
through the AERR are relevant to the inventory requirements of this
final rule (see Section IV.B.2.g of this preamble).
    As noted earlier, the EPA recommends that states consult the SIP
Emissions Inventory Guidance in preparing the inventories required by
this rule. In addition to the AERR, this guidance includes definitions
for data fields that are not required by the AERR, such as seasonal
emissions values and

other fields that are optional in the AERR data collection system. The
EPA is updating the SIP Emissions Inventory Guidance in coordination
with this final rule. It provides specific guidance to states on how to
develop base year inventories for the nonattainment area and attainment
projected inventories for 8-hour ozone, PM2.5, and regional
haze SIPs. While the AERR sets forth requirements for data elements and
definitions, the guidance complements these requirements, defines all
data elements (even those that are voluntary AERR elements), and
indicates how states should prepare and document the data for
attainment plan submissions.
    In the case of prescribed fires and wildfires, the AERR no longer
requires those categories to be submitted, but rather the emissions
data can be optionally provided as an ``Event'' source, which is a day-
specific source at a point location. For this rule as described
earlier, states are required to include prescribed fires and wildfires
for the base year inventory for the nonattainment area and the
attainment projected inventory for the nonattainment area. For this
rule, states are not expected to use the ``Event'' detail to meet their
inventory reporting requirements. Instead, states can report these fire
emissions by county as nonpoint sources are reported.
    f. Emissions Inventories for Support of Modeled Attainment
Demonstrations. This section clarifies the difference between the
inventories required to be a part of a state's Moderate area attainment
plan submission (as described earlier) and other modeling inventories
that are also relevant for attainment planning. While the EPA is not
establishing additional modeling inventory requirements in this rule
(i.e., for which a state must submit an emissions inventory to the
EPA), to meet the attainment demonstration requirements of CAA sections
189(a)(1) and 189(b)(1), states are required to submit either an
attainment demonstration (which includes air quality modeling) to show
how the area will attain the NAAQS by the applicable attainment date or
a demonstration that the area cannot attain by the attainment date. The
modeled attainment demonstration requirements for Moderate areas are
described fully in Section IV.E of this preamble.
    As part of the modeled attainment demonstration, the EPA presumes
that states will need to prepare attainment demonstration modeling
inventories for both a modeled base year and projected attainment year.
Respectively, these are called the ``base year (baseline) inventory for
modeling'' and the ``attainment projected inventory for modeling.''
These inventories contain emissions for all regions (i.e., not just
from sources in the nonattainment area) within the modeling domain
being used for the attainment plan modeling demonstration, which
typically includes counties and even states outside of the
nonattainment area. They include detailed spatial and temporal elements
needed to support air quality modeling. States should follow the
requirements laid out in Section IV.E of this preamble and the
procedures described in the SIP Emissions Inventory Guidance and the
Air Quality Modeling Guidance to meet the minimum requirements for
documentation and emissions summaries supporting modeling
demonstrations.
    The base year inventory and projected attainment year inventory
include emissions from only within the nonattainment area. The EPA
expects that modeling inventories will be consistent with those
nonattainment area inventories; however, some exceptions may exist.
Where possible, the nonattainment area base year and projected
attainment year inventories can be a sum (for annual data) or average
(for PM2.5 season-day data) of day-specific or hour-specific
data used for modeling. In some cases, however, annual or season-day
data may not be sufficient for modeling purposes. For example, greater
spatial detail (gridded rather than county total) and temporal detail
(hourly rather than annual) are needed for on-road mobile modeling
inventories as compared to the base year inventory for the
nonattainment area. Rather, for the nonattainment area base year
inventory, one goal is to allow for the repeatability of the approach
in order to create average-season-day or annual inventories to help
meet other attainment plan requirements, such as RFP or motor vehicle
emissions budgets established for transportation conformity purposes.
That goal is not necessarily compatible with the modeling need for
greater spatial and temporal detail, which requires much greater effort
and expense than is practical for RFP or establishing motor vehicle
emissions budgets. In cases where some differences are unavoidable,
states should attempt to promote consistency where feasible.
    g. Using AERR (40 CFR part 51, subpart A) Inventory Submission to
Meet the Requirement for the Base Year Inventory for the Nonattainment
Area. The AERR includes both triennial and annual statewide reporting
requirements, with more extensive reporting requirements for triennial
inventory years. All AERR submissions are required to be made
electronically. For the interim annual inventories, reporting is
limited to emissions data from only the larger point sources (Type
``A'' sources), as defined by Appendix A of 40 CFR part 51, subpart A.
For the triennial inventories, lower point source thresholds are given
in Appendix A, consistent with the definition of major sources in 40
CFR part 70, and data from all other sources of emissions must be
reported as from either nonpoint or mobile sources on a county basis.
    In the past, some states have incorrectly asserted that their AERR
submission meets the requirements for base year inventories required by
other implementation rules. To avoid confusion, the EPA explains here
the limited circumstances under which the AERR emissions inventories
will be considered to meet the base year inventory requirement for
Moderate nonattainment areas. The following conditions must be met to
use AERR inventories for attainment planning:
    (1) The AERR emissions inventory must have gone through the notice
and public hearing requirements of CAA sections 110(a)(1) and
110(a)(2).
    (2) The AERR emissions inventory includes all sources of emissions
and all pollutants required for the base year inventory for the
nonattainment area. This is only possible if the year for the base year
inventory for the nonattainment area aligns with a triennial AERR year,
because the data system implementing the AERR only accepts emissions
from point sources and not other source categories in non-triennial
years.
    (3) The EPA's inventory data system must be accepting data for the
inventory year being submitted. Inventories are allowed to be submitted
to the AERR for a given year for only a limited time during the
development cycle of the National Emissions Inventory.
    (4) The AERR submission must include emissions from all sources
required for the base year inventory for the nonattainment area
consistent with 40 CFR 51.1008(a)(1), and must include mobile source
emissions in nonattainment areas (instead of simply providing inputs or
other data that is allowed under the AERR). In some cases, the AERR
requirement can be met without actually ``submitting'' emissions; for
example, states may elect to accept the EPA estimates for some nonpoint
emissions sectors. Accepting EPA emissions does not meet the
requirements of CAA section 172(c)(3) or this rule. In addition, the
AERR revision finalized in February 2015 (80 FR 8787) replaces the
prior requirement of reporting onroad mobile and nonroad

mobile source emissions with a requirement for reporting the input
parameters that can be used to run the EPA models to generate the
emissions. If choosing to use an AERR submission to meet the base year
inventory for the nonattainment area requirement, the state should
submit the nonattainment area emissions, irrespective of the options
provided to meet the AERR requirements. Because the ``statewide''
emissions are actually provided for individual point sources and
counties, the EPA believes that the AERR submission can be sufficient
for most PM2.5 nonattainment areas.
    h. Mobile Source Emissions Models. A key part of emissions
inventory development includes estimating mobile source emissions. For
all of the mobile source inventories used for PM2.5 NAAQS
implementation, states should use the latest emissions models available
at the time that the attainment plan inventory is developed.\58\ In
general, for states other than California that choose to fulfill
various modeling requirements by using the latest EPA emissions model,
the latest approved version of the MOVES model should be used to
estimate emissions from onroad transportation sources. States should
use the latest available planning emission inputs including, but not
limited to, vehicle miles traveled (VMT), speeds, fleet mix, SIP
control measures and fuels. The current version of MOVES is available
at http://www.epa.gov/otaq/models/moves/index.htm. The appropriate EPA-
approved model(s) should similarly be used for California onroad source
emissions.\59\
---------------------------------------------------------------------------

    \58\ Section 172(c)(3) of the CAA requires that emission
inventories be based on the most comprehensive, accurate and current
information available. To do so, air agencies should use the most up
to date method for estimating emissions.
    \59\ At this time, the California onroad mobile model is called
EMFAC2014.
---------------------------------------------------------------------------

    When using MOVES, states should follow the most current version of
the MOVES Technical Guidance, available at http://www.epa.gov/otaq/models/moves/index.htm. MOVES includes multiple options for estimating
and processing emissions that could result in different emissions
inventories. The EPA recommends that states use the same approach in
any analysis that compares two or more emissions cases (e.g., different
control scenarios, different years). If different approaches are taken
for inventories that serve different purposes (for example, between
inventories developed for air quality modeling, which may require
greater temporal and spatial detail, and inventories used as the motor
vehicle emissions budget), states should seek to understand and
minimize any differences in results. For example, an approach may be
used for the modeled attainment demonstration that uses gridded
temperatures and other meteorological data, but this approach could be
too burdensome for use in the base year inventory for the nonattainment
area. If a state chooses to use MOVES to create emissions inventories
for purposes of RFP and establishing motor vehicle emissions budgets
for transportation conformity purposes, it must use the same MOVES
approach in the base year inventory for the nonattainment area, and
using a straightforward MOVES approach without gridded meteorology is
more reasonable for that purpose.
    Likewise, if states choose to fulfill various inventory
requirements by using the latest EPA emissions model, the most current
version of the NONROAD model or its successor must be used for
estimates of nonroad mobile source emissions, preferably with state-
supplied model input data. States can alternatively develop
technologically equivalent or superior state-specific nonroad emissions
estimates, but should explain why their approach gives a better
estimate than the EPA model. For nonroad sources not estimated by the
NONROAD model, the best available methods should be used, and the EPA
recommends that states refer to the SIP Emissions Inventory Guidance
for more information on emissions from these sources. Links to Federal
Register documents and policy guidance memos on the latest approved
versions of MOVES and NONROAD can be found at http://www3.epa.gov/otaq/models.htm.
3. Comments and Responses
    Comment: Several commenters pointed out the uncertainties
associated with ammonia emissions and organic matter emissions from
livestock and fertilizer application sources, including in data
developed by the EPA such as the National Emissions Inventory.
Commenters pointed to the data available through the National Air
Emissions Monitoring Study (NAEMS) for use in developing improved
ammonia estimation approaches from livestock activities, and asserted
that the EPA cannot move forward with SIP implementation requirements
that implicate livestock and poultry farmers without using the NAEMS
data. The commenters stated that not only is this technically unsound,
but that the idea of moving forward on regulating livestock operations
without the most critical tool for establishing requirements is a
violation of the spirit of the consent agreements \60\ and the NAEMS.
---------------------------------------------------------------------------

    \60\ In 2005, the EPA offered animal feeding operations (AFOs)
an opportunity to participate in a voluntary consent agreement
referred to as the Air Compliance Agreement. Under the Agreement,
participating AFOs provided the funding for the National Air
Emissions Monitoring Study (NAEMS)--a 2 year, nationwide emissions
monitoring study of the animal confinement structures and manure
storage and treatment units in the broiler, egg-layer, swine, and
dairy industries (see 70 FR 4958).
---------------------------------------------------------------------------

    Response: The EPA acknowledges that there is some uncertainty in
quantifying ammonia emissions and other PM2.5 precursors
from source categories such as livestock and fertilizer application.
This uncertainty extends to the emissions and chemical composition of
VOC and PM2.5, which also have an impact on ambient
PM2.5. These uncertainties have an impact on attainment
demonstrations because they cause uncertainty in the modeling done to
demonstrate future attainment of the PM2.5 standard.
However, the EPA disagrees with the assertion that these uncertainties
should eliminate certain pollutants from consideration for control
measures or should slow progress on attainment planning.
    Emissions uncertainty is a fact of air quality planning and cannot
be avoided. Despite uncertainties in inventories of all kinds
throughout the NAAQS program, great progress in improving air quality
has been made through the attainment planning process and the
implementation of control measures selected in part based on modeled
attainment demonstrations. While emissions uncertainties remain, enough
information is available for PM2.5 implementation planning
purposes. The requirements contained in this final rule may drive
further improvements in our understanding of emissions, and while the
EPA strives to provide approaches for estimating emissions from a
variety of source categories, the CAA places the burden for developing
accurate emissions inventories on the states. The CAA does not allow
for implementation of the NAAQS to be put on hold until all emissions
uncertainties are eliminated. In fact, in spite of numerous
uncertainties, states have developed emissions inventories for
PM2.5 and PM2.5 precursors and performed modeling
for PM2.5 attainment demonstrations for the previous 1997
and 2006 NAAQS over the last 10 or more years.
    Updated emissions estimating methodologies for animal feeding
operations are under development using data collected during the period
2007-2009 from representative operations pursuant to the National Air
Emissions

Monitoring Study.\61\ For the 2008 and 2011 national emission
inventories, the EPA compiled state and county-level ammonia emissions
estimates using information from state and local governments, the USDA
Census of Agriculture and National Agriculture Statistical Service, and
from existing ammonia emissions models. A new approach in development
for use in the 2014 NEI uses the NAEMS data to improve the EPA's
approach for estimating county-total emissions. The EPA expects that
this update and other uses of the NAEMS data will help to reduce
uncertainties in current ammonia inventories and will improve the
quality of future emissions inventories needed for implementing the
PM2.5 NAAQS. The EPA disagrees that implementation planning
should wait until NAEMS results are fully available. The EPA continues
to make progress in using these data; however, the full use and
implementation of new methods based on these data is not a prerequisite
for progress on considering ammonia as a PM2.5 precursor for
the NAAQS implementation purposes. Moreover, in order for a state to
demonstrate a precursor's insignificance (as necessary under this rule
before excluding it from certain control or planning requirements), in
some cases it may need to move forward without waiting until the NAEMS
results are fully available. The EPA and USDA are continuing to work
collaboratively to better understand agricultural ammonia related
emissions in order to more accurately represent the emissions and
impacts of ammonia in relation to PM2.5.
---------------------------------------------------------------------------

    \61\ For more information on the NAEMS study, see: http://www3.epa.gov/airquality/agmonitoring/.
---------------------------------------------------------------------------

    Comment: Commenters supported the EPA's proposed approach to
require distinct emissions for filterable and condensable
PM2.5. Commenters asserted that this proposed requirement
created an additional inventory requirement beyond what is already
required in the AERR. Commenters also asserted that this requirement
places an unnecessary burden on states and industry.
    Response: The EPA disagrees with the assertion that an additional
inventory requirement has been imposed by this rule. Within the AERR,
40 CFR 51.15(a)(1)(vi) states (with regard to what must be reported):
``Primary PM2.5. As applicable, also report filterable and
condensable components.'' The term ``also'' implies ``in addition to
total primary PM2.5,'' and the phrase ``as applicable'' is
intended to mean when such emissions are emitted from the source. This
requirement has been in place since 2008, providing ample time for
states to ensure compliance with this reporting requirement in advance
of this final rule. Furthermore, the EPA points out that it would be
much more difficult for the EPA to assess (as part of evaluating an
attainment plan) whether states have met the requirement to include
condensable emissions, and thus a complete PM2.5 inventory,
without the states providing condensable emissions as something
separate and distinct from filterable and total PM2.5. In
addition, having a complete emission inventory of filterable and
condensable PM2.5 emissions will enable a state to better
identify contributing sources and develop a more effective plan.
    The EPA also notes that new electric generating units that are
subject to (40 CFR part 60, subpart Da) without PM continuous emissions
monitors (CEMs) have to conduct annual testing for condensable PM using
Method 202 of appendix M of part 51.
    Comment: Some commenters supported the EPA's proposed approach to
require an attainment projected inventory for the nonattainment area.
Other commenters asserted that such an inventory should not be required
because it has not been required before and because the attainment
demonstration is sufficient.
    Response: The EPA disagrees with the latter commenters, noting that
the rationale that such inventories have not been required before is
not in and of itself a reasonable basis on which to exclude such a
requirement now. The purpose of these inventories is well justified by
the need for both the EPA and the public to be able to compare, during
their reviews of the attainment plan, the base year inventory to the
attainment projected inventory. Without such information, it is
extremely difficult for the EPA to assess the projected emissions
changes in the nonattainment area that the state asserts contribute to
attainment. The attainment projected inventory may also play a role in
meeting the RFP requirements of this rule. Furthermore, while the EPA
has not explicitly required submittal of an attainment projected
inventory in regulation, many states have developed such future year
inventories as part of attainment demonstrations and have submitted
them as part of PM2.5 attainment plans in the past, thus
demonstrating their viability and utility.
    Comment: Commenters supported the EPA's proposed approach to allow
seasonal inventories. Some commenters requested the use of clear
language stating an allowance for episode-specific inventories in lieu
of seasonal inventories.
    Response: The EPA agrees with the commenters that for some source
categories, seasonally averaged winter conditions would not be
sufficient to represent the conditions leading to violations of the 24-
hour PM2.5 standard. As described in Section IV.B.2.c of
this preamble, some modifications have been made to the explanation of
seasonal inventories to clarify that it would be reasonable to use an
episodic average from the modeled attainment demonstration in some
cases.

C. Pollutants To Be Addressed in the Plan

    Under subpart 4 of the CAA, states are presumptively required to
analyze and evaluate emissions reduction measures for all sources of
direct PM2.5 and PM2.5 precursors (i.e.,
SO2, NOX, VOC and ammonia) in developing
PM2.5 attainment plans. Direct PM2.5 emissions
include both filterable and condensable PM2.5 emissions. See
further discussion of filterable and condensable PM2.5
emissions in the background section (Section II of this preamble) and
in the emissions inventory requirements for Moderate area attainment
plans (Section IV.B of this preamble). Thus, a state must evaluate
control measures for sources of filterable and condensable
PM2.5 emissions as part of an approvable control strategy
for a Moderate PM2.5 nonattainment area.
    With regard to PM2.5 precursors, Section III of the
preamble describes that the rule provides for the possibility that the
state may demonstrate that nonattainment area emissions of a particular
precursor may not make a significant contribution to PM2.5
levels that exceed the standard in the area, or that emissions
reductions of the precursor may not be needed for expeditious
attainment. Thus, the rule presumptively requires the state to evaluate
potential control measures for all four precursors, but the state may
not need to address one or more requirements for a particular precursor
with an approvable precursor demonstration.

D. Attainment Plan Control Strategy

1. Background on Attainment Planning and the Evaluation of Control
Measures
    a. Summary of Proposal. The proposal included an overview of the
statutory requirements and general guidance associated with attainment
planning and evaluation of control measures.
    b. Final Rule. The following overview of statutory requirements and
general

guidance remains unchanged except as discussed in this final rule.
    The attainment planning requirements of subparts 1 and 4 were
established to ensure that two important CAA goals are met: (i) That
states implement measures that provide for attainment of the
PM2.5 NAAQS as expeditiously as practicable, but not later
than the statutory attainment date; and (ii) that states adopt
effective emissions reduction strategies in nonattainment areas. The
Moderate nonattainment area attainment date is as expeditiously as
practicable, but not later than the end of the sixth calendar year
after designation.
    CAA section 172(c) of subpart 1 of the CAA describes the general
attainment plan requirement for RACM and RACT, requiring that
attainment plan submissions ``provide for the implementation of 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) and shall provide for
attainment'' of the NAAQS.\62\ The attainment planning requirements in
subpart 4 that are specific to PM10 (including
PM2.5) likewise impose upon states an obligation to develop
attainment plans that require RACM and RACT for sources of direct
PM2.5 and PM2.5 precursors within a Moderate
nonattainment area. CAA section 189(a)(1)(C) requires that states with
areas classified as Moderate have attainment plan provisions to assure
that RACM/RACT are implemented by no later than 4 years after
designation of the area.\63\ The EPA reads CAA sections 172(c)(1) and
189(a)(1)(C) together to require that attainment plans for Moderate
nonattainment areas must provide for the implementation of RACM and
RACT for existing sources of PM2.5 and PM2.5
precursors in the nonattainment area as expeditiously as practicable
but no later than 4 years after designation.\64\ The terms RACM and
RACT are not defined within subpart 4, nor do the provisions of subpart
4 specify how states are to meet the RACM and RACT requirements.
However, the EPA's longstanding guidance in the 1992 General Preamble
helps inform our interpretation of RACM and RACT for the purpose of
implementing the PM2.5 NAAQS.
---------------------------------------------------------------------------

    \62\ Because in CAA section 172(c) the term ``reasonably
available control measures,'' or RACM, also includes ``reasonably
available control technology,'' or RACT, this document uses the
abbreviation ``RACM/RACT'' to represent these requirements
collectively, where appropriate.
    \63\ States with areas later reclassified as ``Serious''
nonattainment areas under subpart 4 must also develop and submit
later plans to meet additional requirements for Serious areas. See
40 CFR 51.1003(b).
    \64\ This interpretation is consistent with guidance described
in the General Preamble. See 57 FR 13498 (April 16, 1992), at page
13540.
---------------------------------------------------------------------------

    The EPA's guidance on RACM for sources of PM10 and
PM10 precursors under subpart 4 in the General Preamble and
Serious area Addendum includes the following: (i) A recommended list of
potential measures to reduce PM10 for states to consider;
\65\ (ii) an emphasis on state evaluation of the technological and
economic feasibility of potential control measures to determine whether
such measures are reasonably available for implementation; (iii) an
expectation that the state will provide a reasoned explanation for a
decision not to adopt a particular control measure, including those
measures recommended to the state in public comments or at a public
hearing; and (iv) a discussion that in some cases partial
implementation of an emissions reduction program may be considered RACM
when full implementation would be infeasible within the given Moderate
area timeframe.\66\ Thus, the RACM requirement under subpart 4 applies
to all types of sources and is not focused only on forms of control
that are technology-based.
---------------------------------------------------------------------------

    \65\ The appendices to the General Preamble, 57 FR 18070 (April
28, 1992), included sections on available fugitive dust control
measures, available residential wood combustion measures, and
available prescribed burning control measures.
    \66\ See 57 FR 13498 (April 16, 1992), at pages 13540-41. See
also the Addendum.
---------------------------------------------------------------------------

    With respect to RACT requirements, the EPA's guidance in the
General Preamble includes the following: (i) RACT has historically been
defined as ``the lowest emission limit that a source is capable of
meeting by the application of control technology that is reasonably
available considering technological and economic feasibility''; (ii)
RACT generally applies to stationary sources, both stack and fugitive
emissions; (iii) major stationary sources (i.e., sources with potential
to emit 100 tons per year or more of direct PM2.5 or any
PM2.5 precursor) should be the minimum starting point for a
state's RACT analysis, but states are recommended to evaluate RACT for
smaller stationary sources as needed for attainment and considering the
feasibility of controls; \67\ and (iv) it is possible that a State
could demonstrate that an existing source in an area should not be
subject to a control technology especially where such technology is
unreasonable in light of the area's attainment needs, or such
technology is infeasible. In such a case, it could be concluded that no
control technology is ``reasonably available,'' and RACT for the source
could be considered to be no additional control.\68\ Thus, the RACT
requirement under subpart 4 is primarily focused on stationary sources
and forms of emissions control that are technology-based.
---------------------------------------------------------------------------

    \67\ Ibid.
    \68\ Ibid.
---------------------------------------------------------------------------

    The appendices to the General Preamble noted that reducing air
emissions may not justify adversely affecting other resources, for
example, by increasing pollution in bodies of water, creating
additional solid waste disposal problems or creating excessive energy
demands. An otherwise available control technology may not be
reasonable if these other environmental impacts are sufficiently
adverse and cannot reasonably be mitigated. A state may consider a
control measure for direct PM2.5 or a PM2.5
precursor not reasonable if, considering the availability of mitigating
adverse impacts of that control on pollution of other media, the
control would not, in the state's reasoned judgment, provide a net
benefit to public health and the environment. It should be noted that,
in many past situations, states and owners of existing sources have
adopted control technologies for direct PM2.5 and/or
PM2.5 precursors with known energy penalties and some
adverse effects on other media, based on the reasoned judgment that
installation of such technology would result in a net benefit to public
health and the environment. States should consider this before
determining that a control technology is not reasonable because it may
have other, negative environmental impacts that are on balance
marginal.
    This final rule specifies the basic requirements that states must
meet in identifying and selecting the complete suite of measures needed
for an attainment plan submission for a Moderate PM2.5
nonattainment area. This preamble, together with the General Preamble,
provides further description of the recommended process for states to
follow in meeting these requirements. Under this process, the specific
determination of RACM and RACT is to be made within the broader context
of assessing control measures for all stationary, area and mobile
sources of direct PM2.5 and PM2.5 precursors that
would collectively contribute to meeting the Moderate area attainment
date as expeditiously as practicable.\69\
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    \69\ In Sierra Club v. EPA, 294 F.3d 155 (D.C. Cir. 2002), the
court stated, in upholding the EPA's statutory interpretation of
RACM, that the CAA does not compel a state to consider a measure
without regard to whether it would expedite attainment.

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    The final rule requires that all moderate area plans contain RACM,
which is defined as any technologically and economically feasible
measure that can be implemented in whole or in part within 4 years
after the effective date of designation of a PM2.5
nonattainment area and that achieves permanent and enforceable
reductions in direct PM2.5 emissions and/or PM2.5
precursor emissions from sources in the area. RACM includes reasonably
available control technology (RACT). The EPA recommends that to meet
this definition, the state should follow a process by which it first
identifies all sources of emissions of direct PM2.5
(including filterable and condensable PM2.5) and all
PM2.5 precursors in the nonattainment area, and all
potential control measures to reduce emissions from those source
categories.\70\ The state next determines if any of the identified
potential control measures are not technologically feasible and whether
any of the identified technologically feasible control measures are not
economically feasible. Measures that are not necessary for attainment
need not be considered as RACM/RACT.\71\
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    \70\ The proposal described situations where some control
measures could be exempted from consideration at the beginning of
the analytical process. For example, control measures for a
particular precursor would not need to be evaluated if the air
agency submits an acceptable precursor demonstration as described in
Section III of the preamble.
    \71\ This has been the EPA's longstanding interpretation of
RACM/RACT in CAA sections 172(c)(1) and 189(a)(1)(C), which were
enacted as part of the amendments to the Act in 1990. Even prior to
the 1990 amendments, the EPA interpreted the statutory term RACM to
encompass only those measures ``necessary to assure reasonable
further progress and attainment by the required date.'' 44 FR 20375
(Apr. 4, 1979); see 40 CFR 51.1(o) (1972) (defining RACT in similar
terms); 42 U.S.C. 7502(b)(2) (1988) (requiring RACM in the precursor
to current CAA section 172(c)(1)). In the 1990 amendments to the
Act, Congress enacted a ``[g]eneral savings clause'' stating that
``[e]ach regulation, standard, rule, notice, order and guidance
promulgated or issued by [EPA] under this chapter, as in effect
[before the 1990 Amendments], shall remain in effect according to
its terms.'' 42 U.S.C. 7415. Since the passage of the 1990
amendments, the EPA's interpretation of RACM and RACT as
encompassing only those measures necessary to advance attainment has
been upheld in multiple U.S. Circuit Courts of Appeals. See NRDC v.
EPA, 571 F.3d 1245, 1251-1253 (D.C. Cir. 2009); Sierra Club v. EPA,
314 F.3d 735, 743-744 (5th Cir. 2002); Sierra Club v. EPA, 294 F.3d
155, 162 (D.C. Cir. 2002). But cf. Sierra Club v. EPA, 793 F.3d 656
(6th Cir. 2015) (holding that an area must have subpart 1 RACM/RACT
approved into its SIP prior to redesignation, regardless of whether
the area is attaining the NAAQS).
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    Measures that can only be implemented after the 4-year deadline for
RACM and RACT, but before the end of the sixth calendar year following
designation, are defined in the final rule as ``additional reasonable
measures.'' \72\ The EPA has created this new definition based on the
recognition that in some areas there could be emission reduction
strategies that still could be implemented beginning 4 years after
designation through the attainment date that could help to improve air
quality and attain the standard expeditiously in the area. Note also
that the state has discretion to require reductions from any source
inside or outside of a PM2.5 nonattainment area (but within
the state's boundaries) in order to fulfill its obligation to
demonstrate attainment in a PM2.5 nonattainment area as
expeditiously as practicable, and it may need to require emissions
reductions on sources located outside of a PM2.5
nonattainment area if such reductions are needed in order to provide
for expeditious attainment of the PM2.5 NAAQS.
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    \72\ In addition to the statutory requirements under CAA
sections 172(c)(1) and 189(a)(1)(C) for RACM and RACT, CAA section
172(c)(6) requires that a state's attainment plan for a
nonattainment area ``include enforceable emission limitations, and
such other control measures, means or techniques (including economic
incentives such as fees, marketable permits, and auctions of
emission rights), as well as schedules and timetables for
compliance, as may be necessary or appropriate to provide for
attainment of such standard in such area by the applicable
attainment date specified in this part.'' The EPA interprets this
statutory provision to require a state to identify, select and
implement additional measures to those identified as RACM and RACT
for the area if needed to provide for timely attainment of the area.
In the EPA's proposed approach, the EPA describes criteria for
identifying and selecting ``additional reasonable measures'' for
sources of direct PM2.5 and PM2.5 precursors
in a Moderate nonattainment area which may be necessary in order to
bring the area into expeditious attainment.
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    Lastly, the final rule requires the state to perform an analysis
(typically an air quality modeling analysis) to determine the earliest
practicable attainment date for the area. This analysis should take
into account projected emissions reductions associated with existing
federal and state regulations, plus any additional reductions that
would be achieved due to new control measures that would be needed for
expeditious attainment.
    In the case of a Moderate area that can demonstrate it can attain
by the statutory attainment date without implementing all reasonably
available control measures (i.e. RACM/RACT and additional reasonable
measures), the state would not be required to adopt certain otherwise
reasonable measures if the state demonstrates that collectively such
measures would not enable the area to attain the standard at least 1
year earlier (i.e., ``advance the attainment date'' by 1 year). The EPA
has long applied this particular test to satisfy the statutory
provision related to an area demonstrating attainment ``as
expeditiously as practicable.'' \73\ The EPA continues to believe that
this approach provides an appropriate degree of flexibility to a state
to tailor its attainment plan control strategy to the actual attainment
needs of a particular PM2.5 nonattainment area. In the case
of a Moderate area that cannot demonstrate that it will practicably
attain by the statutory attainment date, the state would be required to
evaluate potential control measures for sources in the nonattainment
area and adopt all reasonable measures (i.e., RACM and RACT, and any
``additional reasonable measures'').
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    \73\ The term ``expeditious attainment'' is used throughout this
proposal to describe the ability of a nonattainment area to attain
``as expeditiously as practicable'' based on the test described
here.
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    The following sections of the preamble describe the steps of the
control measure evaluation process in more detail, and include
discussion of the consideration of public comments as appropriate.
2. Step 1: Identify Sources of Emissions
a. Summary of Proposal
    The proposal stated that the identification of all sources of
emissions of direct PM2.5 (including filterable and
condensable PM2.5) and all four PM2.5 precursors
in the nonattainment area is the starting point for the state's
analysis of potential control measures. It was noted that an exception
to this comprehensive review requirement might be possible if the final
rule includes a policy that would allow a state to demonstrate that one
or more precursors in a nonattainment area do not significantly
contribute to PM2.5 levels that exceed the standard. If such
a demonstration were approved by EPA, then the state would not be
required to adopt control measures for the precursor.
    The proposal also included discussion of a possible de minimis
source category exemption concept for Moderate areas. Under the
approach, the analysis and identification of ``de minimis source
categories'' for Moderate areas would occur early in the planning
process, before potential control measures are identified or attainment
modeling is conducted. The proposal recognized the challenges
associated with defining ``source categories.'' The proposal also
included potential options on how source categories could be defined,
and requested comment on using the North American Industry

Classification System (NAICS) (which provides a detailed hierarchy of
numeric codes for different industries and process types) at the two,
four, or six digit levels.
    The proposal also presented the concept of a possible bright line
ambient impact threshold for determining whether a source category
should be considered de minimis (in the event a de minimis concept is
adopted). Comments were requested on two options: (1) No bright line
threshold; and (2) a threshold in the range of 1-3 percent of the
relevant PM2.5 NAAQS. This range was selected because it was
similar to the de minimis source category threshold range (2.0-3.3
percent of the PM10 NAAQS) included in the 1994 Serious Area
Addendum.
b. Final Rule
    Section 172(c)(3) of the CAA requires that attainment plans for
PM2.5 nonattainment areas include a ``comprehensive,
accurate, current inventory of actual emissions from all sources of the
relevant pollutant or pollutants.'' Consistent with the proposal, the
final rule maintains the policy that the state must begin the control
consideration process by identifying potential control measures for all
the sources included in the most recently available emissions inventory
for the nonattainment area. The inventory must include emissions
information for all existing major stationary sources as point sources,
nonpoint sources (as defined by 40 CFR 51.50) including non-major point
sources, and mobile sources of direct PM2.5 (including
filterable and condensable PM2.5) and PM2.5
precursors in the nonattainment area. Section IV.B of this preamble
provides a detailed discussion of emission inventory requirements.
    The rule requires that a state must identify all of the sources
reflected in the nonattainment area's base year inventory as the
initial step in developing reasonable control measures for the area, as
each of these sources may play a role in the area's PM2.5
problem. A state would need to consider all inventoried sources of
direct PM2.5 emissions (including filterable and condensable
PM2.5) and sources of all four scientific PM2.5
precursors as it conducts its determination of reasonable control
measures for an area.
    Some commenters suggested that subpart 4 only provides authority to
regulate precursors from major stationary sources and not from other
types of sources, such as area or mobile sources. However, EPA
disagrees with these commenters, given that the CAA provides an
overarching requirement to attain the standard as expeditiously as
practicable, PM2.5 precursor emissions play a very
significant role in fine particle concentrations nationally, non-major
sources are important sources of precursor emissions, and nothing in
the statutory requirements for RACM and BACM limits these requirements
only to major stationary sources.
    As discussed in the previous section, the final rule provides that
states may develop a precursor demonstration showing that a particular
PM2.5 precursor does not contribute significantly to
PM2.5 levels that exceed the standard. If such a
demonstration is approved by the EPA, then the state would not be
required to adopt control measures for the precursor. Note that the
state would still be obligated to evaluate and adopt control measures
from a source if the source has emissions of direct PM2.5
and/or the remaining PM2.5 precursors that must be
controlled in the plan.
    The EPA received a diverse set of comments on whether to include a
de minimis source category exemption policy. Some commenters questioned
why an up-front (i.e., before analysis of potential control measures)
source category by source category exemption should be included in the
final rule in the first place, when the traditional RACT/RACM policy
approach for the NAAQS implementation has enabled states not to adopt
otherwise reasonable control measures if after analyzing potential
control measures it is determined that such measures are not needed for
expeditious attainment. These commenters also suggested that a de
minimis source category approach would undermine any RACM/RACT analysis
to evaluate whether a collection of measures could advance the
attainment date by a year, because a de minimis exemption policy would
potentially allow for an area to exempt many categories which together
could have a substantial ambient impact. Other commenters noted that
providing a source category exemption in one nonattainment area would
give those companies a competitive advantage over the same types of
sources in other areas.
    A number of commenters supported the de minimis source category
concept because they believed it could result in a reduced burden in
the control measure evaluation stage and help avoid regulating sources
with limited impact on PM2.5 levels. However, a number of
commenters also expressed concern about the analytical resources that
might be needed to conduct air quality modeling for a de minimis source
category analysis. To address this analytical concern, some commenters
suggested that the EPA include an emissions-based threshold (e.g., tons
per day) rather than an air quality based threshold, and allow for its
use only if controls on the source are not needed for expeditious
attainment. However, the commenters did not address the fact that the
air quality impact of a specific tons per day rate could vary widely
from one pollutant to another within a particular nonattainment area.
Other commenters noted that the NAICS system does not provide
categories for nonpoint sources, and that this issue would need to be
addressed if the NAICS approach were to be included in the final rule.
Other commenters suggested that the rule not have a de minimis
threshold at all but include the ability for the state to propose de
minimis source categories to the EPA on a case-by-case basis.
    After taking the range of comments on the de minimis source
category concept into consideration, the EPA has decided to not
finalize a de minimis source category approach for Moderate areas. The
EPA is persuaded by commenters who argued it is not necessary, and
believes that without this concept, the final rule will nevertheless
provide sufficient flexibility in the Moderate area control measure
analysis and attainment demonstration process due to the availability
of precursor demonstrations, considerations of case-specific factors in
determining technical and economic feasibility, and the longstanding
ability for the state not to adopt certain otherwise reasonable
measures if they are not needed for expeditious attainment. The EPA
also finds that from a technical perspective, it would be very
challenging to implement a de minimis source category process in a
consistent manner nationally without clear guidelines describing how
narrowly or how broadly a de minimis exemption could apply, or how the
technical analysis would need to be performed. The EPA agrees with
commenters that NAICS codes do not provide an appropriately
comprehensive approach for defining source categories for this purpose.
We note that a de minimis source category exemption process has been
available in PM10 NAAQS implementation guidance (the
Addendum) since 1994, and remains available. In many PM10
areas, it is relatively straightforward to identify the predominant
source categories contributing to the NAAQS violations (such as direct
PM emissions from dust or wood smoke), and therefore to be able to
identify what categories might be considered de

minimis. However, implementation of the PM2.5 NAAQS presents
more complex challenges. Precursors and their contribution to
secondarily formed PM play a much greater role in PM2.5
nonattainment areas than in PM10 nonattainment areas. In
addition, the relative impact of each precursor to local
PM2.5 concentrations varies from area to area. For these
reasons, a de minimis source category concept for PM2.5 is
not included in this final rule.
c. Comments and Responses
    Any additional comments received on this section are addressed in
the Response to Comments document found in the docket for this action.
3. Step 2: Identify Existing and Potential Control Measures
a. General Guidance
i. Summary of Proposal
    The proposal preamble described general guidance for identifying
existing and potential control measures.
ii. Final Rule
    The guidance remains largely unchanged from the proposal. The
state's compilation of existing and potential control measures \74\
should be sufficiently broad to provide a basis for identifying all
technologically and economically feasible controls that may be RACM or
RACT for sources of direct PM2.5 (including filterable and
condensable PM2.5) and PM2.5 precursor emissions
in the nonattainment area at issue. Because RACM applies to area and
mobile sources as well as stationary sources, states should identify
and consider control measures for all types of sources.\75\
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    \74\ Note that the term ``control measures'' as used in this
preamble broadly represents a range of enforceable approaches for
reducing emissions. These enforceable approaches include, but are
not limited to, installation of control technology, process changes,
a change in fuel use, limitations on use or operation of a
particular pollutant-emitting device, equipment replacement, dust
minimization practices, and road paving.
    \75\ Additional guidance on evaluating potential control
measures is provided in the previous Section III.D.1 of this
preamble, Background.
---------------------------------------------------------------------------

    It is important to note that the emission inventory provisions of
this rule require states with sources of direct PM2.5 to
include emissions data for both filterable PM2.5 and
condensable PM2.5 in the base year inventory for the
nonattainment area. For some types of sources, condensable emissions
can be much larger than filterable emissions, in some cases by ten
times or more. Because the availability of condensable PM2.5
emissions data has been limited to date but more data will become
available through nonattainment planning efforts, the EPA recommends
that states pay particular attention to identifying potential control
measures for source categories with substantial condensable emissions.
If measures are found to be technically and economically feasible for
reducing condensable PM2.5 emissions as well as filterable
PM2.5 emissions from a source, the state will need to adopt
a new emissions limit for the source that accounts for both the
filterable and condensable portions, and includes requirements for
ensuring compliance using source test methods updated in 2011.\76\
---------------------------------------------------------------------------

    \76\ See 75 FR 80118 (December 21, 2010), revisions to test
methods for measuring condensable PM emissions from stationary
sources (Method 202).
---------------------------------------------------------------------------

    The control measure evaluation process described in this section
generally allows states to apply reasoned judgment as they identify
potential control measures for sources of direct PM2.5 and
PM2.5 precursors in their respective nonattainment areas. In
section 51.1009(a)(3)(iii) of the final rule, the state is required to
include a complete and reasoned explanation to support its selection
and rejection of control measures as part of the attainment plan
submission for any Moderate nonattainment area.
    Existing control measures. As a starting point when identifying
candidate control measures, a state should include an initial list of
control measures 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 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 the
existence of 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 control technology analyses to address emissions for previous
RACM/RACT analyses or for other statutory purposes. Some of these
determinations may have been done relatively recently, while other
determinations may be several years old. A state may not simply rely on
a previous RACM or RACT determination or other control technology
analysis for a particular source or source category, regardless of how
recently it was performed, when developing the attainment plan for a
PM2.5 NAAQS. Past experience has shown that due to ongoing
innovation, cost-effective control technologies and process
alternatives for many sectors continue to be developed, and new
reasonable opportunities to reduce emissions in the future are expected
to be available for existing sources, particularly those with
technology determinations made several years ago. For this reason, the
state must determine whether the existing controls or emissions
reduction approach at the source can be updated or improved with
reasonably available controls or strategies to achieve increased levels
of emission reduction. In cases where a stationary source has installed
new state-of-the-art emissions controls fairly recently (e.g., within
the last 3 years), the state technically would still need to provide a
RACT analysis for the source, but in such cases it may be appropriate
to find that existing controls satisfy the RACT requirement. Based on
this policy, the state's updated RACM and RACT analyses will represent
the most thorough, up-to-date review of control measures for its
PM2.5 nonattainment area. The collection of existing control
measures, any updated RACT/RACM determinations, and potential new
control measures can then be considered together by the state as part
of a comprehensive analysis to ensure the area will attain
expeditiously. The EPA notes, however, that the more recently this
analysis has been done, the less effort is expected to be needed to
verify that it is up to date.
    Potential control measures. In addition to identifying and
reviewing existing control measures for sources in a Moderate
PM2.5 nonattainment area, a state must develop a
comprehensive list of potential new control measures. This process
should involve close coordination between the state, source owners,
municipalities, and other interested stakeholders. The potential
measures should also have a strong technical basis. Analysis of
emission inventory data summaries, fine particle speciation monitoring
data and source apportionment air quality modeling data can help
identify key sectors contributing to the PM2.5 problem in an
area. Other analyses to characterize the seasonal variation of
PM2.5

concentrations and associated meteorology may help inform the state in
identifying contributing sources and potential control measures.
    Information about potential control measures and control
technologies is available from a number of sources. One important
source of information is the combined regulatory experience of other
states. A compilation of existing control regulations that are on the
books in other states can be a useful starting point for identifying
potential control measures. Another source of information is the EPA's
Office of Air Quality Planning and Standards (OAQPS) ``Menu of Control
Measures'' document, available online at http://www3.epa.gov/ttn/naaqs/pdfs/MenuOfControlMeasures.pdf. This document was developed to provide
information useful in the development of local emissions reduction and
the 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,
and can be searched for control approaches that address specific
pollutants. 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.\77\ Again, the EPA recognizes that 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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    \77\ Links are provided to a number of national, state and local
air quality agency sites from the EPA's PM2.5 Web site:
http://www3.epa.gov/pm/measures.html.
---------------------------------------------------------------------------

iii. Comments and Responses
    Any additional comments received on this section are addressed in
the Response to Comments document found in the docket for this action.
b. Managing Emissions From Wildfire and Wildland Prescribed Fire.
i. Proposed Rule
    The EPA proposed to recommend as guidance but not as a requirement
of the final rule that, if wildfire impacts are significant,
contributing to exceedances of the standard, then states should
consider RACM for wildfires (which RACM could include a required
program of prescribed fires). The EPA also proposed to recommend that
states should consider RACM for managing emissions from prescribed
fires (including those prescribed fires conducted to reduce future
wildfire emissions). The proposal noted that information is available
from the DOI and the USDA Forest Service on smoke management programs
and basic smoke management practices (BSMP). The EPA requested comment
on the concept of, and practical considerations associated with RACM
for wildfire and RACM for 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.
ii. Final Rule
    Wildfire can make a large contribution to air pollution (including
PM2.5), and wildfire events can threaten public safety.
These effects can be mitigated through management of wildland
vegetation, including through prescribed fire. Such mitigation can help
manage the contribution of fires to PM2.5 levels in
nonattainment areas. Prescribed fire (and some wildfires) can mimic the
natural processes necessary to maintain fire dependent ecosystems,
minimizing catastrophic wildfires and the risks they pose to safety,
property and air quality.
    Upon consideration of public comments and further consultation with
other federal agencies, the EPA recommends, as guidance for states as
they implement the final rule, that states follow a different approach
to addressing RACM for wildland fire than the approach that the EPA
proposed to recommend. Before explaining this recommendation further,
the EPA wishes to clarify that the recommendation is focused on
wildland fire management. There are other uses of prescribed fire and
other types of burning that occur in nonattainment areas, or that
affect downwind nonattainment areas, such as burning of land clearing
debris, agricultural burning, and burning of logging slash on land
where the primary purpose of the logging is for commercial timber
sale.\78\ The challenges with applying the traditional nonattainment
planning framework that are raised in this discussion are particular to
wildland fire, and the EPA believes that addressing these other uses of
prescribed fire does not present nearly the same level of challenge,
and thereby can still be accommodated within the nonattainment planning
framework. For example, where these other types of burning currently
contribute to PM2.5 levels in a nonattainment area, states
may, with an adequate technical demonstration, be able to take credit
for reductions resulting from improvement in smoke management
techniques for these types of prescribed fire where the improvement
results in a demonstrated reduction in impacts in the nonattainment
area. The remainder of this discussion is not meant to address these
categories, and is instead focused on prescribed fire on wildlands.
---------------------------------------------------------------------------

    \78\ The EPA notes that some wildland logging operations are
conducted for the same purposes as prescribed fire (e.g., reducing
fuel load, ecosystem benefits, etc.). The fact that some of the
removed trees may be sold as timber does not make commercial timber
sale the primary purpose of such operations.
---------------------------------------------------------------------------

    The EPA also wants to clarify that it is not the intention to in
any way discourage federal, state, local or tribal agencies or private
land owners from taking situation-appropriate steps to minimize impacts
from prescribed fire emissions on wildland. The EPA encourages all land
owners and managers to apply appropriate basic smoke management
practices to reduce emissions from prescribed fires, especially where a
state has determined that prescribed fires are a significant source
affecting air quality. The EPA understands that the federal land
managers (FLMs) apply these measures routinely and will be available to
consult with other agencies and private parties interested in doing the
same.
    However, for several reasons, the EPA does not believe it would be
effective policy or technically appropriate to recommend that control
measures for wildland fire be adopted into the SIP as enforceable
measures and credited for emissions reductions (of PM2.5 and
precursors) that would help the area

attain the standard.\79\ Instead, EPA recommends that PM2.5
nonattainment plans (and in particular the attainment demonstrations)
not expressly account for expected air quality changes over the
planning period resulting from changes in the use of wildland
prescribed fire to reduce future wildfires, or air quality changes over
the planning period resulting from changes in wildland fire emissions
due to a program of prescribed fire or due to any other cause including
climate change. In most cases, state attainment demonstration modeling
should assume that wildland prescribed fire and wildfire emissions in
the attainment year will be equal to, and have the same temporal and
geographic pattern as, those assumed in the baseline inventory year.
---------------------------------------------------------------------------

    \79\ These reasons include concerns raised by commenters about
the difficulties associated with requiring or even encouraging
states to incorporate wildland fire emissions into existing
nonattainment planning procedures and practices under the CAA; high
year-to-year variability and unpredictability with emissions from
wildland fires; uncertainty in the amount of credit to give for
reduced wildfire within the planning period and in the amount of
benefit that exists after accounting for increases in prescribed
fires within the planning period; and finally, the fact that air
quality data actually influenced by fire events may ultimately be
excluded under the provisions of the Exceptional Events Rule.
---------------------------------------------------------------------------

    The EPA acknowledges that some temporal and spatial patterns of
fire emissions must still be assumed in the attainment demonstration in
order to ensure that the required air quality modeling results in a
realistic physical and chemical environment and a correspondingly
realistic model response against which to analyze the changes from
categories where express accounting of changes is still being done.
This rule is not intended to constrain the options for states regarding
the appropriate assumptions to make for fire emissions. Rather, it
simply recommends that once this base level is established,
PM2.5 plans should not attempt to expressly project changes
over the planning period in emissions from wildfires or prescribed
fires on wildland within the nonattainment area, or in upwind areas
included in the modeling domain, that are due to variability in
wildfire occurrence or changes in the use of prescribed fire or other
wildland fire management practices. Moreover, the EPA anticipates that
changes in spatial and temporal patterns of wildfire will likewise be
too uncertain for them to be allowed to have the effect of reducing or
increasing the control requirement on conventional anthropogenic
sources. The EPA therefore recommends that baseline wildland fire
emissions should generally be held constant over the planning period,
regardless of whether wildland fire management practices by land
managers are expected, and possibly encouraged, to change.
    States still have flexibility in determining how best to represent
baseline wildland fire emissions. As noted earlier, base year emission
inventories for the nonattainment areas should represent the conditions
leading to nonattainment and be consistent with inventories used for
modeling. For fires, the EPA additionally encourages states to use a
representative mix of prescribed fire and wildfire in their
inventories. In the past, some plans under previous PM2.5
NAAQS have estimated the actual fire emissions and temporal and spatial
patterns from a given year and used this estimate as the assumed future
baseline for planning, while others have used average emissions over
multiple years. Other approaches may be appropriate as well. Moreover,
regardless of the approach used, the EPA still encourages states to
submit actual wildfire and prescribed fire activity data that are
critical to developing emissions estimates to the NEI as suggested in
the AERR.
    A consequence of the recommendation of not expressly accounting for
changes in wildland fires in attainment demonstrations is that measures
to reduce emissions from wildland fires, such as prescribed fire for
wildland wildfire prevention and mitigation purposes or smoke
management programs and BSMP for prescribed fires in wildland, need not
be included as RACM for the respective fire types. This is because the
changes in emissions due to such measures would not be accounted for in
determining what is necessary for attainment and/or what would advance
the attainment date, which is how the EPA is recommending that RACM be
determined. So, for example, in an area that can attain in 6 years with
measures that do not address wildland fire, the EPA does not recommend
that states attempt to quantify whether increased prescribed fire could
advance the attainment date by 1 year, due to aforementioned
difficulties associated with such quantification.
    To be clear, nothing about this policy regarding RACM is intended
to suggest that fires should be ignited in wildland (or elsewhere)
without regard to the air quality or public health consequences. As
noted earlier, the EPA believes these consequences are important to
address, and intends to engage in dialogue with the FLMs, air agencies,
tribes, state and private land owners and other stakeholders at
appropriate times, such as during the process for the development of
land management plans, about how land managers determine when and where
prescribed fire is appropriate for particular wildlands and how to
identify and implement appropriate mitigation measures. The policy
simply makes clear the EPA's view regarding its recommendation for RACM
for wildland fires.
    The EPA notes that this recommendation regarding RACM differs
somewhat from the recommendation that was offered in the preamble as
guidance to states as they implement the EPA's recent SIP Requirements
Rule for the 1997 and 2008 ozone NAAQS. The reasons for the strategy
outlined earlier apply equally well to attainment demonstrations for
the ozone NAAQS, and so EPA hereby makes the same recommendation for
implementation of these ozone NAAQS as well. This recommendation,
offered here in the same manner as the prior recommendation, supersedes
the prior recommendation on RACM for wildfire in the preamble to the
final SIP Requirements Rule for the 1997 and 2008 ozone NAAQS. The EPA
will convey this revised recommendation to the air agencies that are
working to prepare these ozone SIPs. The EPA also anticipates making
this recommendation as part of our planned rulemaking on implementation
of the 2015 ozone NAAQS. Note that this discussion pertains only to the
RACM policy, and that other aspects of the fire discussions in the
ozone SIP Requirements Rule remain applicable.
    Finally, the EPA notes that, because a significant element of the
rationale for this policy is the uncertainty in the timing of
wildfires, we may reconsider this recommendation in the future, if
adequate tools emerge that allow for predicting fire emissions with
sufficient specificity. However, even if such tools emerge, due to
inherent uncertainties it may be impossible to satisfactorily
incorporate the use of such information into an attainment
demonstration framework.
iii. Comments and Responses
    The EPA received many comments expressing agreement with EPA's
recognition of the importance of wildland prescribed fire, and
welcoming continued dialogue among states, the EPA, and other federal
agencies on how best to ensure that land managers have adequate
management tools available, including prescribed fire and some
wildfire, but also to ensure that use of these tools does not result in
unhealthy air. The EPA intends to engage in such dialogue.

    Some commenters also took positions on how specifically to define
RACM for wildfires, ranging from required smoke management plans to
simply stating that fires themselves are RACM with no further measures
required. In light of the fact that EPA did not propose specific
guidance on defining RACM for wildfires and typically does not define
RACM for specific categories, and the fact that EPA is not recommending
that states include RACM as proposed, we are not providing further
guidance in response to those comments. Similarly, regarding baseline
fire emissions, some commenters provided detailed suggestions regarding
approaches to calculating baselines based not on actual fires (which
may include periods when fires were suppressed) but on science-based
fire regimes, fire return intervals and ecosystem types, including
characteristics of wildland vegetation. The EPA notes that this
guidance is not establishing or recommending any particular approach to
calculating baseline fire emissions.
c. RACT for EGUs
i. Summary of Proposal
    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.\80\
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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    \80\ See the Federal Register published on April 25, 2007 (72 FR
20586, 20623, 20624 and 20625).
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    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.\81\ 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.82 83 In that proposal, the EPA explained that given
the explicit wording of CAA 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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    \81\ 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 CAA 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).
    \82\ 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.
    \83\ 79 FR 32892 (June 9, 2013).
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    Accordingly, in the proposal the EPA stated that it did not intend
to include 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 stated that it 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.
ii. Final Rule
    The final rule maintains the proposed policy approach as described
earlier. As required by the CAA, states are required to analyze what
constitutes RACM and RACT for EGUs in each nonattainment area, just as
they are required to do for all other types of sources.
iii. Comments and Responses
    Any additional comments received on this section are addressed in
the Response to Comments document found in the docket for this action.
4. Step 3: Determine Whether an Available Control Measure or Technology
Is Technologically Feasible
a. Summary of Proposal
    The proposal cited longstanding guidance from the General Preamble
regarding factors to consider when determining the technological
feasibility of a potential control measure or control technology, and
it requested comment on the factors. These factors included 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. One sentence in the
proposal stated: ``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 . . .'' \84\
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    \84\ See the proposed PM2.5 SIP requirements rule (80
FR 15340, 15373)
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b. Final Rule
    Several comments addressed the EPA's inclusion of the social
acceptability factor in the proposal. In reviewing this issue, the EPA
determined that this factor actually has not been identified as a
factor in the EPA's longstanding guidance, and thus was
mischaracterized in the proposal. Nevertheless, some commenters
supported inclusion of the factor because no other factor is presented
to help limit or eliminate a potential measure with strong public
opposition. Other commenters that opposed use of such a factor
suggested that including it in the final rule could allow a state to
reject almost any control measures that is otherwise found to be
technically and economically feasible.
    When the EPA issued a proposed PM2.5 NAAQS
implementation rule in 2005, it requested comment on the same social
acceptability factor, and ultimately did not include social
acceptability as a factor for determining RACM in the final 2007
PM2.5 implementation rule. In the 2007 final rule, however,
the EPA stated:

``Therefore, given the concerns raised by commenters that establishment
of `social acceptability' as a factor in the RACM analysis is without
basis in the CAA and might result in inappropriate skewing of control
strategies, we have removed this term from the final rule. We
reiterate, however, that capability of effective implementation and
enforcement are relevant considerations in the RACM analysis, even
though public `unpopularity' is not. Moreover, in assessing the
efficacy of measures and the credit they should be given in the context
of attainment demonstrations or RFP calculations, EPA believes that
such considerations are important.'' For the same reason it was not
included in the previous implementation rule, the EPA has decided to
not include the social acceptability factor in this final rule as well.
See 40 CFR 51.1009(a)(3)(i).
    The following guidance is similar to what was presented in the
proposal but has been updated to exclude the social acceptability
factor:
    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.
    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.\85\ 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. A state may consider such factors in
determining whether a control measure is or is not technologically
feasible to implement.\86\
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    \85\ See the Federal Register published on April 16, 1992 (57 FR
13498, 13540 and 13541).
    \86\ 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 applying it here for
Moderate area RACM determinations.
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    In addition, with respect to determining whether a given control
measure might not be technologically feasible for an area or mobile
source, the EPA also retains its longstanding practice that a state may
consider relevant factors in conducting its analysis, 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.
c. Comments and Responses
    Comment: Some commenters stated that the EPA should make clearer in
its rule and guidance that some categories of sources, particularly
those such as animal and crop production, do not lend themselves to
national determinations of best control practices; instead, these types
of sources should be evaluated on nonattainment area specific
conditions in determining the appropriate level of control measures.
    Response: The EPA agrees that nonattainment area-specific
conditions are important factors when considering emission reduction
options. States need to consider the feasibility of all identified
options that have been demonstrated to reduce PM2.5 and
PM2.5 precursors to determine whether such measures are
appropriate for use in a particular PM2.5 nonattainment
area.
    The EPA believes the determination of best control practices for
any operation, particularly for animal production or crop production
operations, should be a case-specific process. The process should start
with the identification of PM2.5 and PM2.5
precursor emissions from the operation. Then it should consider which
of the measures for reducing PM2.5 and PM2.5
precursors in a particular PM2.5 nonattainment area are
technically and economically feasible for a particular operation. The
EPA recognizes that there are a number of factors specific to each
operation that could determine whether a potential emission reduction
measure is technically and economically feasible for implementation.
    Although the EPA is not making any national determinations of best
control practices for animal production and crop production operations,
we do note that there are many relevant references on potential
emissions reduction options, including the Agricultural Air Quality
Conservation Measures Reference Guide for Cropping Systems and Land
Management.\87\ The EPA and USDA jointly developed this document to
identify measures that have been demonstrated to reduce emissions and
describe factors related to the applicability of each measure. A
companion document is under development by the EPA and USDA that will
identify potential emission reduction approaches for livestock
operations. Additionally, USDA's Natural Resources Conservation Service
(NRCS) provides a list of approved practices in managing air emissions
of concern for particulate matter, ozone, greenhouse gas, and odor-
related issues.\88\ A number of regulatory and non-regulatory programs
are already being implemented (in nonattainment and attainment areas
alike) to reduce emissions of PM2.5 and PM2.5
precursors from agricultural operations. Finally, a large body of
information is available on topics such as feed management, livestock
housing, conservation tillage, road use and other topics from federal
agencies, states, industry groups, academic institutions, and
international organizations.
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    \87\ See the EPA Web site at https://www3.epa.gov/airquality/agriculture/.
    \88\ See the USDA NRCS Air Quality Technical Resources at http://www.nrcs.usda.gov/wps/portal/nrcs/main/national/air/quality/.
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5. Step 4: Determine Whether an Available Control Measure or Technology
Is Economically Feasible
a. Summary of Proposal
    The proposal described that in the 1992 General Preamble, EPA's
longstanding interpretation of the term ``economic feasibility'' in the
context of evaluating potential RACM and RACT has included a
presumption that it is reasonable for similar sources to bear similar
costs of emissions reductions, even if they are in different
nonattainment areas or different states. The proposal indicated that
this presumption was not included in the 2007 implementation rule for
the PM2.5 NAAQS that the EPA had received a petition for
reconsideration with respect to this issue, and that EPA had granted
this petition in 2011.89 90 The March

2015 proposed PM2.5 SIP requirements rule indicated the
EPA's intention to not adopt the economic feasibility factors as
described in the 2007 rule, but to return to the original
interpretation from the 1992 General Preamble, including the
presumption that it is reasonable for similar sources to bear similar
costs of emissions reductions.
---------------------------------------------------------------------------

    \89\ ``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.
    \90\ 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.
---------------------------------------------------------------------------

    The proposal also characterized past guidance from the 1992 General