[Federal Register Volume 83, Number 242 (Tuesday, December 18, 2018)]
[Proposed Rules]
[Pages 64774-64795]
[FR Doc No: 2018-27257]

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 52

[EPA-R09-OAR-2017-0728; FRL-9988-01-Region 9]

Approval and Promulgation of Air Quality State Implementation
Plans; California; Plumas County; Moderate Area Plan for the 2012 PM2.5
NAAQS

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: The Environmental Protection Agency (EPA) is proposing to
approve most elements of the state implementation plan (SIP) revisions
submitted by California to address Clean Air Act (CAA or ``Act'')
requirements for the 2012 annual fine particulate matter
(PM2.5) national ambient air quality standards (NAAQS or
``standards'') in the Plumas County Moderate PM2.5
nonattainment area (``Portola nonattainment area''). The SIP revisions
are the ``Portola Fine Particulate Matter (PM2.5) Attainment
Plan'' submitted on February 28, 2017, and the 2019 and 2022
transportation conformity motor vehicle emission budgets (``budgets'')
submitted on December 20, 2017. We refer to these submittals
collectively as the ``Portola PM2.5 Plan'' or ``Plan.'' The
EPA is proposing to approve the following elements of the Portola
PM2.5 Plan: The 2013 base year emissions inventories, the
reasonably available control measure/reasonably available control
technology (RACM/RACT) demonstration, the attainment demonstration, the
reasonable further progress (RFP) demonstration, the quantitative
milestones, and the budgets for 2019 and 2021. The EPA is not proposing
any action at this time on the contingency measures in the Portola
PM2.5 Plan.

DATES: Any comments must arrive by January 17, 2019.

ADDRESSES: Submit your comments, identified by Docket ID No. EPA-R09-
OAR-2017-0728 at https://www.regulations.gov, or via email to John
Ungvarsky, at<EMAIL_ADDRESS>For comments submitted at
Regulations.gov, follow the online instructions for submitting
comments. Once submitted, comments cannot be removed or edited from
Regulations.gov. For either manner of submission, the EPA may publish
any comment received to its public docket. Do not submit electronically
any information you consider to be Confidential Business Information
(CBI) or other information whose disclosure is restricted by statute.
Multimedia submissions (audio, video, etc.) must be accompanied by a
written comment. The written comment is considered the official comment
and should include discussion of all points you wish to make. The EPA
will generally not consider comments or comment contents located
outside of the primary submission (i.e., on the web, cloud, or other
file sharing system). For additional submission methods, please contact
the person identified in the FOR FURTHER INFORMATION CONTACT section.
For the full EPA public comment policy, information about CBI or
multimedia submissions, and general guidance on making effective
comments, please visit http://www2.epa.gov/dockets/commenting-epa-dockets.

FOR FURTHER INFORMATION CONTACT: John Ungvarsky, EPA Region IX, (415)
972-3963<EMAIL_ADDRESS>
SUPPLEMENTARY INFORMATION: Throughout this document, ``we,'' ``us'' and
``our'' refer to the EPA.

Table of Contents

I. Background for Proposed Action
II. Clean Air Act Requirements for Moderate PM2.5
Nonattainment Area Plans
III. Completeness Review of the Portola PM2.5 Attainment
Plan
IV. Review of the Portola PM2.5 Plan
V. Summary of Proposed Actions and Request for Public Comment
VI. Statutory and Executive Order Reviews

I. Background for Proposed Action

    Under section 109 of the CAA, the EPA has established NAAQS for
certain pervasive air pollutants (referred to as ``criteria
pollutants'') and conducts periodic reviews of the NAAQS to determine
whether they should be revised or whether new NAAQS should be
established. The EPA sets the NAAQS for criteria pollutants at levels
required to protect public health and welfare.\1\ Particulate matter is
one of the criteria pollutants for which the EPA has established
health-based standards. The CAA requires states to submit regulations
that control particulate matter emissions.
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    \1\ For a given air pollutant, ``primary'' national ambient air
quality standards are those determined by the EPA as requisite to
protect the public health. ``Secondary'' standards are those
determined by the EPA as requisite to protect the public welfare
from any known or anticipated adverse effects associated with the
presence of such air pollutant in the ambient air. CAA section
109(b).
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    Particulate matter includes particles with diameters that are
generally 2.5 microns or smaller (PM2.5) and particles with
diameters that are generally 10 microns or smaller (PM10).
It contributes to effects that are harmful to human health and the
environment, including premature mortality, aggravation of respiratory
and cardiovascular disease, decreased lung function, visibility
impairment, and damage to vegetation and ecosystems. Individuals
particularly sensitive to PM2.5 exposure include older
adults, people with heart and lung disease, and children.\2\
PM2.5 can be emitted by sources directly into the atmosphere
as a solid or liquid particle (``primary PM2.5'' or ``direct
PM2.5'') or can be formed in the atmosphere (``secondary
PM2.5'') as a result of various chemical reactions among
precursor pollutants from sources such as nitrogen oxides
(NOX), sulfur dioxide (SO2), volatile organic
compounds (VOC), and ammonia.\3\
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    \2\ 78 FR 3086, 3088 (January 15, 2013).
    \3\ EPA, Air Quality Criteria for Particulate Matter, No. EPA/
600/P-99/002aF and EPA/600/P-99/002bF, October 2004.
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    On July 18, 1997, the EPA revised the NAAQS for particulate matter
to add new standards for PM2.5.\4\ The EPA established
primary and secondary annual and 24-hour standards for
PM2.5. The annual standard was set at 15.0 micrograms per
cubic meter ([micro]g/m\3\)

based on a 3-year average of annual mean PM2.5
concentrations, and the 24-hour (daily) standard was set at 65
[micro]g/m\3\ based on the 3-year average of the annual 98th percentile
values of 24-hour PM2.5 concentrations at each population-
oriented monitor within an area.\5\
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    \4\ 62 FR 38652.
    \5\ The primary and secondary standards were set at the same
level for both the 24-hour and the annual PM2.5
standards.
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    On October 17, 2006, the EPA retained the annual average NAAQS at
15 [micro]g/m\3\ but revised the level of the 24-hour PM2.5
NAAQS to 35 [micro]g/m\3\ based on a 3-year average of the annual 98th
percentile values of 24-hour concentrations.6 7
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    \6\ Under EPA regulations at 40 CFR part 50, the primary and
secondary 2006 24-hour PM2.5 NAAQS are attained when the
annual arithmetic mean concentration, as determined in accordance
with 40 CFR part 50, Appendix N, is less than or equal to 35
[micro]g/m\3\ at all relevant monitoring sites in the subject area,
averaged over a 3-year period.
    \7\ 71 FR 61144.
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    On January 15, 2013, the EPA finalized the 2012 PM2.5
NAAQS, including a revision of the annual standard to 12.0 [micro]g/
m\3\ based on a 3-year average of annual mean PM2.5
concentrations, and retaining the current 24-hour standard of 35
[micro]g/m\3\ based on a 3-year average of the 98th percentile of 24-
hour concentrations.\8\
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    \8\ 78 FR 3086.
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    Following promulgation of a new or revised NAAQS, the EPA is
required by CAA section 107(d) to designate areas throughout the nation
as attaining or not attaining the NAAQS. The EPA designated and
classified the Portola area as ``Moderate'' nonattainment for the 2012
annual PM2.5 standards based on ambient monitoring data that
showed the area was above 12.0 [micro]g/m\3\ for the 2011-2013
monitoring period.\9\ For the 2011-2013 period, the annual
PM2.5 design value for the Portola area was 12.8 [micro]g/
m\3\ based on monitored readings at the 161 Nevada Street and 420
Gulling Street monitors.\10\
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    \9\ 80 FR 2206 (January 15, 2015).
    \10\ From 2000 through early 2013, the Portola PM2.5
monitoring site was located at 161 Nevada Street. In 2013, the site
was relocated to 420 Gulling Street.
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    The Portola PM2.5 nonattainment area includes the City
of Portola (``Portola''), which has a population of approximately 2,100
and is located at an elevation of 4,890 feet in an intermountain basin
isolated by rugged mountains. Portola averages 20 inches of
precipitation annually. From October through March the nonattainment
area has very cold temperatures with the average daily low temperature
of approximately 22 degrees Fahrenheit. The combination of mountains,
cold temperatures, and elevation can cause inversions and impair
PM2.5 dispersion, especially during the winter. For a
precise description of the geographic boundaries of the Portola
PM2.5 nonattainment area, see 40 CFR 81.305.
    The local air district with primary responsibility for developing a
plan to attain the 2012 annual PM2.5 NAAQS in this area is
the Northern Sierra Air Quality Management District (NSAQMD or
``District''). The District worked cooperatively with the California
Air Resources Board (CARB) in preparing the Portola PM2.5
Plan. Under state law, authority for regulating sources under state
jurisdiction in the Portola nonattainment area is split between the
District, which has responsibility for regulating stationary and most
area sources, and CARB, which has responsibility for regulating most
mobile sources.

II. Clean Air Act Requirements for Moderate PM2.5 Nonattainment Area
Plans

    With respect to the statutory requirements for attainment plans for
the 2012 annual PM2.5 NAAQS, the general CAA part D
nonattainment area planning requirements are found in subpart 1, and
the Moderate area planning requirements specifically for particulate
matter are found in subpart 4.
    The EPA has a longstanding general guidance document that
interprets the 1990 amendments to the CAA, commonly referred to as the
General Preamble for the Implementation of Title I of the Clean Air Act
Amendments of 1990 (``General Preamble'').\11\ The General Preamble
addresses the relationship between the subpart 1 and the subpart 4
requirements and provides recommendations to states for meeting certain
statutory requirements for particulate matter attainment plans. As
explained in the General Preamble, specific requirements applicable to
Moderate area attainment plan SIP submissions for the particulate
matter NAAQS are set forth in subpart 4 of part D, title I of the Act,
but such SIP submissions must also meet the general attainment planning
provisions in subpart 1 of part D, title I of the Act, to the extent
these provisions ``are not otherwise subsumed by, or integrally related
to,'' the more specific subpart 4 requirements.\12\
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    \11\ General Preamble, 57 FR 13498 (April 16, 1992).
    \12\ 57 FR 13538.
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    To implement the PM2.5 NAAQS, the EPA has also
promulgated the ``Fine Particle Matter National Ambient Air Quality
Standard: State Implementation Plan Requirements; Final Rule''
(hereinafter, the ``PM2.5 SIP Requirements Rule'').\13\ The
PM2.5 SIP Requirements Rule provides additional regulatory
requirements and guidance applicable to attainment plan submissions for
the PM2.5 NAAQS, including the 2012 annual PM2.5
NAAQS at issue in this action.
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    \13\ 81 FR 58010, August 24, 2016.
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    The subpart 1 statutory requirements for attainment plans include:
(i) The section 172(c)(1) requirements for RACM/RACT and attainment
demonstrations; (ii) the section 172(c)(2) requirement to demonstrate
RFP; (iii) the section 172(c)(3) requirement for emissions inventories;
(iv) the section 172(c)(5) requirements for a nonattainment new source
review (NNSR) permitting program; and (v) the section 172(c)(9)
requirement for contingency measures.
    The more specific subpart 4 statutory requirements for Moderate
PM2.5 nonattainment areas include: (i) The section
189(a)(1)(A) and 189(e) NNSR permit program requirements; (ii) the
section 189(a)(1)(B) requirements for attainment demonstrations; (iii)
the section 189(a)(1)(C) requirements for RACM; and (iv) the section
189(c) requirements for RFP and quantitative milestones. Under subpart
4, states with Moderate PM2.5 nonattainment areas must
provide for attainment in the area as expeditiously as practicable but
no later than December 31, 2021, for the 2012 PM2.5 annual
NAAQS. In addition, under subpart 4, direct PM2.5 and all
precursors to the formation of PM2.5 are subject to control
unless the EPA approves a demonstration from the State establishing
that a given precursor does not contribute significantly to
PM2.5 levels that exceed the PM2.5 NAAQS in the
area.\14\
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    \14\ 40 CFR 51.1006 and 51.1009.
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III. Completeness Review of the Portola PM2.5 Attainment Plan

    CAA sections 110(a)(1) and (2) and 110(l) require each state to
provide reasonable public notice and opportunity for public hearing
prior to the adoption and submission of a SIP or SIP revision to the
EPA. To meet this requirement, every SIP submission should include
evidence that adequate public notice was given and an opportunity for a
public hearing was provided consistent with the EPA's implementing
regulations in 40 CFR 51.102.
    Both the District and CARB satisfied applicable statutory and
regulatory requirements for reasonable public

notice and hearing prior to adoption and submission of the Portola
PM2.5 Plan. The District provided a 30-day public comment
period prior to its January 23, 2017 public hearing to adopt the main
SIP submission.\15\ CARB provided the required public notice and
opportunity for public comment prior to its February 16, 2017 public
hearing and adoption of the main SIP submission.\16\ CARB then adopted
its supplemental SIP submission pertaining to 2019 and 2022
transportation conformity motor vehicle emission budgets at its October
26, 2017 Board meeting after reasonable public notice.\17\ Each
submission includes proof of publication of notices for the respective
public hearings. We find, therefore, that the Portola PM2.5
Plan meets the requirements for reasonable notice and public hearings
in CAA sections 110(a) and 110(l).
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    \15\ The District public notice posted on its website for
January 23, 2017 public hearing (undated); February 14, 2017 proof
of publication from Plumas County News of public notice for January
23, 2017 public hearing; December 14, 2016 proof of publication from
Feather Publishing Co., Inc. of public notice that public notice for
January 23, 2017 public hearing published in the Feather River
Bulletin, Indian Valley Record, and Portola Reporter during the week
beginning December 14, 2016; and NSAQMD Governing Board Resolution
2017-01, ``In the Matter of Adopting the Portola Fine Particulate
Matter (PM2.5) Attainment Plan (Portola Plan) as required
by the Federal Clean Air Act,'' January 13, 2017.
    \16\ CARB, Notice of evidence of listserve publication,
``arbcombo--Notice of Public Meeting for February 16, 2017,'' and
``Notice of Public Meeting to Consider the Approval of the Portola
PM2.5 State Implementation Plan,'' both dated January 13,
2017; CARB Board Resolution 17-2, ``Portola PM2.5 State
Implementation Plan,'' February 16, 2017.
    \17\ CARB Board Resolution 17-28, ``Supplemental Transportation
Conformity Emissions Budgets for the Portola Fine Particulate Matter
(PM2.5) Attainment Plan,'' October 26, 2017.
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    CAA section 110(k)(1)(B) requires the EPA to determine whether a
SIP submission is complete within 60 days of receipt. This section also
provides that any plan that the EPA has not affirmatively determined to
be complete or incomplete will become complete by operation of law six
months after the date of submission. The EPA's SIP completeness
criteria are found in 40 CFR part 51, appendix V. The February 28, 2017
and December 20, 2017 SIP submissions became complete by operation of
law on August 28, 2017 and June 20, 2018, respectively.

IV. Review of the Portola PM2.5 Plan

A. Emissions Inventory

1. Requirements for Emissions Inventories
    CAA section 172(c)(3) requires that each SIP include a
``comprehensive, accurate, current inventory of actual emissions from
all sources of the relevant pollutant or pollutants in [the] area . . .
.'' By requiring an accounting of actual emissions from all sources of
the relevant pollutants in the area, this section provides for the base
year inventory to include all emissions that contribute to the
formation of a particular NAAQS pollutant. For the 2012
PM2.5 NAAQS, this includes emissions of direct
PM2.5 as well as the main chemical precursors to the
formation of secondary PM2.5: NOX,
SO2, VOC, and ammonia. Primary PM2.5 includes
condensable and filterable particulate matter.
    A state must include in its SIP submission documentation explaining
how the emissions data were calculated. In estimating mobile source
emissions, a state should use the latest emissions models and planning
assumptions available at the time it develops the SIP submission.
States are also required to use the EPA's ``Compilation of Air
Pollutant Emission Factors'' (AP-42) \18\ road dust method for
calculating re-entrained road dust emissions from paved roads.\19\ The
latest EPA-approved version of California's mobile source emission
factor model is EMFAC2014.\20\
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    \18\ The EPA released an update to AP-42 in January 2011 that
revised the equation for estimating paved road dust emissions based
on an updated data regression that included new emission tests
results.
    \19\ 76 FR 6328 (February 4, 2011).
    \20\ The EMFAC model (short for EMission FACtor) is a computer
model developed by CARB. The EPA approved EMFAC2014 for use in SIP
revisions and transportation conformity at 80 FR 77337 (December 14,
2015).
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    In addition to the base year inventory submitted to meet the
requirements of CAA section 172(c)(3), the State must also submit
future ``baseline inventories'' for the projected attainment year and
each RFP milestone year, and any other year of significance for meeting
applicable CAA requirements.\21\ By ``baseline inventories'' (also
referred to as ``projected baseline inventories''), we mean projected
emissions inventories for future years that account for, among other
things, the ongoing effects of economic growth and adopted emissions
control requirements. The SIP submission should include documentation
to explain how the state calculated the emissions projections.
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    \21\ 40 CFR 51.1007(a), 51.1008(b), and 51.1009(f); see also
U.S. EPA, ``Emissions Inventory Guidance for Implementation of Ozone
[and Particulate Matter] National Ambient Air Quality Standards
(NAAQS) and Regional Haze Regulations,'' available at http://www.epa.gov/sites/production/files/2014-10/documents/2014revisedeiguidance_0.pdf.
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2. Emissions Inventory in the Portola PM2.5 Plan
    The Portola PM2.5 nonattainment area emissions inventory
is typical of a small, high elevation mountain community. There are no
major stationary sources or large industrial sources (existing or
anticipated) and residential wood burning is a significant source of
direct PM2.5. A summary of the planning emissions
inventories for direct PM2.5 and all PM2.5
precursors (NOX, SOX, VOC, and ammonia) \22\ for
the Portola PM2.5 nonattainment area is found in section
III. Detailed inventories for the Portola PM2.5
nonattainment area together with documentation for the inventories are
found in Appendix B of the Plan. CARB and District staff worked jointly
to develop the emissions inventory for the Portola PM2.5
nonattainment area. The District worked with operators of the three
stationary facilities in the nonattainment area to develop the
stationary source emissions estimates.\23\ CARB staff developed the
emissions inventory for mobile sources, both on-road and off-road.\24\
The District and CARB shared responsibility for developing estimates
for the area sources such as residential wood burning and paved road
dust.
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    \22\ The Portola PM2.5 Plan generally uses ``sulfur
oxides'' or ``SOX'' in reference to SO2 as a
precursor to the formation of PM2.5. We use
SOX and SO2 interchangeably throughout this
notice.
    \23\ CARB's facility search engine website shows for 2016 in the
Portola PM2.5 nonattainment area there are no major
stationary sources and only three non-major stationary sources. Two
of the non-major sources reported zero particulate matter (PM)
emissions in 2016, and the third non-major source (i.e., White Cap
Ready Mix #1) reported 1.9 tons per year of PM emissions. For more
information see https://www.arb.ca.gov/app/emsinv/facinfo/facinfo.php.
    \24\ The EPA regulations refer to ``nonroad'' vehicles and
engines whereas California Air Resources Board (CARB) regulations
refer to ``off-road'' vehicles and engines. These terms refer to the
same types of vehicles and engines, and for the purposes of this
action, we will be using CARB's chosen term, ``off-road,'' to refer
to such vehicles and engines.
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    The Plan includes annual average emissions inventories for the 2013
base year and estimated emissions for the 2019, 2021, and 2022 future
baseline years. Future baseline inventories are a projection of the
base year inventory taking into account expected growth trends for each
source category and emission reductions from control measures adopted
prior to January 1, 2013. CARB develops emissions projections by
applying growth and control profiles to the base year inventory.\25\
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    \25\ Portola PM2.5 Plan, Appendix B.
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    Each inventory includes emissions from stationary, area, on-road,
and non-

road sources. The inventories use EMFAC2014 for estimating on-road
motor vehicle emissions.\26\ Re-entrained paved road dust emissions
were calculated using the EPA's AP-42 road dust methodology.\27\
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    \26\ Portola PM2.5 Plan, Appendix B.
    \27\ Id.
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    Table 1 provides a summary of the annual average inventories in
tons per day (tpd) of direct PM2.5 and PM2.5
precursors for the base year of 2013. These inventories provide the
basis for the control measure analysis and the RFP and attainment
demonstrations in the Portola PM2.5 Plan. For a detailed
breakdown of the inventories, see Appendix B, Tables 6-10 in the
Portola PM2.5 Plan.

Table 1--Portola Annual Average Emissions Inventory for Direct PM2.5 and PM2.5 Precursors for the 2013 Base Year
                                                      (tpd)
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                                   Direct PM2.5
            Category                                    NOX             SOX             VOC           Ammonia
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Stationary Sources..............           0.007           0.002           0.000           0.016           0.018
Area Sources....................           0.468           0.048           0.015           0.661           0.142
On-Road Mobile Sources..........           0.005           0.181          0.0003           0.101           0.005
Off-Road Mobile Sources.........           0.011           0.273          0.0001           0.162          0.0001
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    Totals......................           0.490           0.504           0.016           0.940           0.149
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Source: Portola PM2.5 Plan, Section III, Table 3 (p. 24) and Appendix B, Tables 6-10.

3. The EPA's Evaluation and Proposed Action
    The inventories in the Portola PM2.5 Plan are based on
the most current and accurate information available to the State and
District at the time the Plan and its inventories were being developed
in 2015 and 2016, including the latest version of California's mobile
source emissions model, EMFAC2014. The inventories comprehensively
address all source categories in the Portola PM2.5
nonattainment area and were developed consistent with the EPA's
inventory guidance. For these reasons, we are proposing to approve the
2013 base year emissions inventory in the Portola PM2.5 Plan
as meeting the requirements of CAA section 172(c)(3). We are also
proposing to find that the projected baseline inventories in the Plan
provide an adequate basis for the RACM, RFP, and attainment
demonstrations in the Portola PM2.5 Plan.

B. PM2.5 Precursors

1. Precursor Requirements
    The provisions of subpart 4 of part D, title I of the CAA do not
define the term ``precursor'' for purposes of PM2.5, nor do
they explicitly require the control of any specifically identified PM
precursor. The statutory definition of ``air pollutant'' in CAA section
302(g), however, provides that the term ``includes any precursors to
the formation of any air pollutant, to the extent the Administrator has
identified such precursor or precursors for the particular purpose for
which the term `air pollutant' is used.'' The EPA has identified
SO2, NOX, VOC, and ammonia as precursors to the
formation of PM2.5. Accordingly, the attainment plan
requirements of subpart 4 apply to emissions of all four precursor
pollutants and direct PM2.5 from all types of stationary,
area, and mobile sources, except as otherwise provided in the Act
(e.g., in CAA section 189(e)).
    Section 189(e) of the Act requires that the control requirements
for major stationary sources of direct PM10 (which includes
PM2.5) also apply to major stationary sources of
PM10 precursors, except where the Administrator determines
that such sources do not contribute significantly to PM10
levels that exceed the standard in the area. Section 189(e) contains
the only expressed exception to the control requirements under subpart
4 for sources of PM2.5 precursor emissions. Although section
189(e) explicitly addresses only major stationary sources, the EPA
interprets the Act as authorizing it also to determine, under
appropriate circumstances, that regulation of specific PM2.5
precursors from other sources in a given nonattainment area is not
necessary.
    Under the PM2.5 SIP Requirements Rule, a state may elect
to submit to the EPA a ``comprehensive precursor demonstration'' for a
specific nonattainment area to show that emissions of a particular
precursor from all existing sources located in the nonattainment area
do not contribute significantly to PM2.5 levels that exceed
the standard in the area.\28\ Such a comprehensive precursor
demonstration must include a concentration-based contribution analysis
(i.e., evaluation of the contribution of a particular precursor to
PM2.5 levels in the area) and may also include a
sensitivity-based contribution analysis (i.e., evaluation of the
sensitivity of PM2.5 levels in the area to a decrease in
emissions of the precursor). If the EPA determines that the
contribution of the precursor to PM2.5 levels in the area is
not significant and approves the demonstration, the state is not
required to control emissions of the relevant precursor from existing
sources in the current attainment plan.\29\
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    \28\ 40 CFR 51.1006(a)(1).
    \29\ Id.
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    The EPA issued the draft PM2.5 Precursor Demonstration
Guidance (``Draft Guidance'') to provide recommendations to states for
appropriate precursor demonstrations in nonattainment plan SIP
submissions.\30\ For the annual PM2.5 NAAQS, section 2.2 of
the Draft Guidance recommends use of 0.2 [micro]g/m\3\ as a threshold
below which ambient air quality impacts could be considered
``insignificant,'' i.e., impacts that do not ``contribute'' to
PM2.5 concentrations that exceed the NAAQS. When considering
whether a precursor contributes significantly to PM2.5
levels which exceed the NAAQS in the area, a state may also consider
additional factors based on the facts and circumstances of the area. As
to air quality impacts that exceed the 0.2 [micro]g/m\3\ contribution
threshold, states may provide additional support for a conclusion that
a particular precursor does not contribute significantly to ambient
PM2.5 levels that exceed the NAAQS. States may consider
information such as the amount by which the impacts exceed the
recommended contribution threshold, the severity of nonattainment at
relevant monitors and/or grid cell locations in the area, anticipated
growth or loss of sources, analyses of speciation data and

precursor emission inventories, and air quality trends.\31\
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    \30\ EPA Office of Air Quality Planning and Standards,
``PM2.5 Precursor Demonstration Guidance,'' EPA-454/P-16-
001, November 17, 2016 draft, available at https://www.epa.gov/pm-pollution/draft-pm25-precursor-demonstration-guidance.
    \31\ Id. at 17.
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2. Precursor Demonstration in the Plan
    Section V.C. of the Plan contains the State's demonstration that
emissions of SOX, NOX, ammonia, and VOC from all
existing sources in the nonattainment area do not contribute
significantly to PM2.5 levels that exceed the NAAQS. The
demonstration includes a concentration-based portion, a sensitivity-
based portion, and additional relevant information. The concentration-
based portion is summarized in Table 8 of the Plan, based on 2013-2014
species composition data, and used to represent the base year design
value used as the starting point in the rollback attainment
demonstration as described in section IV.E.\32\ All four precursors
together account for 6.3% of the 2013 PM2.5 design value.
Organic matter and elemental carbon, mainly from wood burning, are the
dominant contributors and account for 89% of the 2013 design value.
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    \32\ Portola PM2.5 Plan, 51.
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    For VOC emissions, the corresponding ambient PM2.5
component is anthropogenic Secondary Organic Aerosol (SOA). Based on
comparison to ambient SOA concentrations per ton of total VOC emissions
at other California locations, the State estimated Portola SOA
concentrations of 0.02-0.05 [micro]g/m\3\. The State also noted that
seasonal organic carbon (OC) measurements at Portola are
indistinguishable from background levels during the summer. Because SOA
is a subset of OC, and summer is when SOA is highest due to the warmer
temperatures, the State found that Portola's SOA is comparable to the
0.06 [micro]g/m\3\ observed at nearby background interagency monitoring
of protected visual environments (IMPROVE) sites \33\ and well below
the 0.2 [micro]g/m\3\ contribution threshold.
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    \33\ IMPROVE is a monitoring program managed by the EPA and
other federal and state agencies to assess visibility and aerosol
conditions including PM2.5 species in Class I areas such
as national parks. For more information, go to http://vista.cira.colostate.edu/Improve/reconstructed-fine-mass/.
---------------------------------------------------------------------------

    The ambient species concentrations corresponding to SOX,
NOX, and ammonia were 0.41, 0.46, and 0.48 [micro]g/m\3\,
respectively. Because these are all above the recommended contribution
threshold of 0.2 [micro]g/m\3\, the State conducted a follow-up
sensitivity-based analysis. The sensitivity-based portion of the
precursor demonstration used a variant of the rollback attainment
demonstration based on Positive Matrix Factorization (PMF) as described
in section IV.B.2 of this notice.\34\ The rollback model scales
PM2.5 component concentrations (excluding background)
according to changes in emissions. Ammonium nitrate was scaled
proportional to NOX emissions; ammonium sulfate was scaled
proportional to SOX emissions; and ammonium was scaled
proportional to ammonia emissions. These were all on a conservative
one-to-one basis; that is, a 1% emission change leads to a 1%
concentration change. The sensitivity emission reductions modeled were
10%, 25%, 30%, 50%, and 70%.
---------------------------------------------------------------------------

    \34\ PMF is a multivariate source apportionment method that
attributes PM2.5 observed concentrations to sources
through statistical and meteorological interpretation of data. PMF
is one of several EPA recommended receptor modeling methods for
understanding of source impacts on ambient PM2.5 levels.
---------------------------------------------------------------------------

    As in the attainment demonstration, the precursor demonstration
used the estimated 2021 design value. The PM2.5 effect of
both the sensitivity reductions and the yearly reductions were combined
to estimate the effect on the design value. Table 9 of the Plan lists
the PM2.5 design values resulting from a 10 to 70% reduction
in emissions of each pollutant.\35\ For SOX and ammonia, the
reductions have a negligible impact on the attainment year design
value. The design values listed for the 70% emission reduction show
PM2.5 responses of 0.09 and 0.11 [micro]g/m\3\ for
SOX and ammonia respectively, both well below the
recommended contribution threshold.
---------------------------------------------------------------------------

    \35\ Portola PM2.5 Plan, 53.
---------------------------------------------------------------------------

    For NOX sensitivity, the Plan includes a discussion of
the ambient response to a 30% reduction, 0.16 [micro]g/m\3\, which is
below the 0.2 [micro]g/m\3\ contribution threshold. However, the given
design values for 50% and 70% reductions show responses of 0.26
[micro]g/m\3\ and 0.39 [micro]g/m\3\ respectively, which are above the
recommended contribution threshold.
    Beyond the concentration-based and sensitivity-based analyses, the
Plan provides several pieces of additional information to help assess
the significance of NOX as a PM2.5 precursor.
Table 7 of the Plan shows that NOX emissions in the Portola
nonattainment area, estimated at 0.5 tpd, are far smaller than the
NOX emissions in several other California counties, which
range from 46.5 to 104.0 tpd.\36\ The Plan also shows that 90% of the
NOX emissions in Portola are from mobile sources, which
already are stringently controlled; PM2.5 concentrations
would be not be sensitive to realistic additional control on these
sources.
---------------------------------------------------------------------------

    \36\ Id. at 47.
---------------------------------------------------------------------------

    Supporting supplemental data from CARB shows trends in emissions
and species concentrations during 2002-2016.\37\ The data are for the
Mountain Counties Air Basin, which comprises Plumas County and eight
other similar counties that are also largely rural, wooded areas
spanning the foothills to the crest of the Sierra Nevada mountains.
Ammonia emissions during this period were essentially constant, but
NOX and SOX emissions decreased by 46% and 67%,
respectively. During the same time span, nitrate and sulfate
concentrations decreased by 23% and 16%, respectively. Since nitrate
and sulfate were responding to NOX and SOX
emissions reductions, this suggests that ammonium nitrate formation is
NOX-limited and ammonium sulfate is SOX-limited,
rather than either being ammonia-limited. These observations support a
finding that ammonia is an insignificant PM2.5 precursor,
for which controls would be of little benefit.
---------------------------------------------------------------------------

    \37\ Email with attachment (i.e., Species Trends.xlsx) dated
February 13, 2018, from Kasia Turkiewicz, CARB, to Scott Bohning and
John Ungvarsky, EPA.
---------------------------------------------------------------------------

    Based on its evaluations, the State concluded that additional
controls on PM2.5 precursors would have an insignificant
effect on PM2.5 concentrations, and that precursors need not
be included in the controls analysis.
3. The EPA's Evaluation and Proposed Action
    The comprehensive precursor demonstration provided in the Plan
meets the requirements of 40 CFR 51.1006(a)(1) and is consistent with
the EPA's recommendations in the Draft Guidance. The demonstration
contains a concentration-based contribution analysis for VOC and
sensitivity-based contribution analyses for NOX,
SOX, and ammonia, together with additional information about
the Portola area, as recommended in the Draft Guidance (e.g., emission
inventory and ambient PM2.5 composition data).
    For the SO2 concentration-based analysis, the Plan
states that background sulfate concentrations are 97% of the 0.41
[micro]g/m\3\ measured at Portola. The remaining 3% of the sulfate, or
0.012 [micro]g/m\3\, is attributable to Portola sources. This 3%
contribution from Portola sources to PM2.5 levels above the
NAAQS is well below the EPA's 0.2 [micro]g/m\3\ contribution threshold.
    For the VOC concentration analysis, the Plan provides several
estimates of SOA at Portola. The estimates, which

can be considered ``data analysis techniques'' as described in the
Draft Guidance, are appropriate for refining SOA estimates from
available measurements and provide a convincing case that VOCs do not
contribute significantly to PM2.5 levels that exceed the
NAAQS in the area.
    For NOX, the Plan's estimate for the nitrate
contribution and the corresponding sensitivity to NOX
reductions may be unrealistically high. The PMF modeling results
estimated the secondary nitrate contribution to be 5.1% of the total
PM2.5, whereas the raw chemical composition data estimated
only 3.3%.\38\ In addition, the concentration-based analysis may have
overestimated nitrate concentrations because it does not apply the
sulfate, adjusted nitrate, derived water, inferred carbonaceous balance
approach (SANDWICH) \39\ for reconciling the mass from speciation
measurements with that from the Federal Reference Method (FRM) used for
design values. Because the SANDWICH adjustment generally reduces
nitrate, due to nitrate losses from FRM monitors, the precursor
demonstration in the Plan may be overestimating the amount of nitrate
and the nitrate response to NOX emission reductions. Thus,
the approach used in the Plan results in a more conservative precursor
demonstration.
---------------------------------------------------------------------------

    \38\ Plan, Figure 9, 20, and Table 8, 51.
    \39\ Draft Guidance, 23.
---------------------------------------------------------------------------

    The sensitivity-based precursor analysis relies on the same
methodology as the attainment demonstration, including the very
conservative assumption that the ambient response to NOX
reductions is in a 1:1 ratio to the emission change (on a percent
basis). The responses to SO2 and ammonia reductions were
below the recommended 0.2 [micro]g/m\3\ contribution threshold, but the
response to NOX was above the threshold at 50% and 70%
reductions.
    The Plan includes additional information supporting a conclusion
that NOX emissions do not contribute significantly to
PM2.5 levels that exceed the NAAQS in the area. The
information includes the small size of the NOX emission
inventory relative to other areas and recognition that mobile sources
are already highly controlled. These are indications that ambient
PM2.5 levels would not be sensitive to additional
NOX controls.
    The EPA also considered two other implications of the data provided
with the Plan or as a supplement. The supplemental 2002-2016 emissions
and speciation trends can be used to derive a response factor, the
percent change in nitrate concentration for each percent change in
NOX emissions. Because ammonia emissions are constant, they
provide a reasonable factor to use as the response to reductions of
NOX in the sensitivity analysis. Using 2002-2016 data
results in a NOX response factor of 0.378. Using this in a
variant of the Plan's NOX sensitivity analysis in place of
the 1:1 assumption, the EPA found that the ambient PM2.5
response to a 50% NOX reduction is 0.105 [micro]g/m\3\, and
the response to a 70% reduction is 0.147 [micro]g/m\3\. Both of these
are below the EPA's recommended contribution threshold of 0.2 [micro]g/
m\3\. (The original responses were 0.277 and 0.388 [micro]g/m\3\.)
Since the years 2013-2016 were somewhat anomalous, with some nitrate
increases, the EPA carried out the same exercise using just 2002-2011
data, which resulted in a NOX response factor of 0.625. In
turn, this results in a 50% response of 0.173 [micro]g/m\3\ and a 70%
response of 0.243 [micro]g/m\3\. The 70% response is above but
considerably closer to the recommended 0.2 [micro]g/m\3\ contribution
threshold. When considered in light of the additional information
discussed above, the 70% response supports a conclusion that
NOX emissions do not contribute significantly to
PM2.5 levels that exceed the NAAQS in the area.
    A second implication of the data from the Plan concerns the effect
of a 70% NOX reduction on the year that the Portola area can
attain the NAAQS. Under the PM2.5 SIP Requirements Rule at
40 CFR 51.1009(a)(4)(i), if a Moderate PM2.5 nonattainment
area, such as the Portola area, can show that reducing emission of a
precursor is not necessary for expeditious attainment of the NAAQS and
cannot advance attainment by a year,\40\ then that precursor need not
be controlled for attainment purposes. Even assuming a NOX
reduction of 70%, which is very large in comparison with the historical
reductions of about 6% per year, and assuming an unrealistically
conservative 1:1 nitrate response ratio, the resulting response is
0.388 [micro]g/m\3\, which is less than the average 0.41 [micro]g/m\3\
per year PM2.5 decrease seen during 2019-2021 in the
attainment demonstration. This observation supports a conclusion that
controlling NOX is not necessary for expeditious attainment
of the NAAQS because it would not advance the attainment date by a year
in the Portola nonattainment area.
---------------------------------------------------------------------------

    \40\ 81 FR 58010, 58020 (August 24, 2016).
---------------------------------------------------------------------------

    The EPA is proposing to approve the State's demonstration that
emissions of PM2.5 precursors (i.e., SOX,
NOX, ammonia, and VOC) from all existing sources located in
the nonattainment area do not contribute significantly to
PM2.5 levels that exceed the standards in the area. If the
EPA finalizes this proposal, the State and District would not be
required to control emissions of these precursors from existing sources
in the Portola PM2.5 Plan for purposes of the 2012 annual
PM2.5 NAAQS. The State, District, and the EPA will reexamine
this issue if the Portola area fails to attain the NAAQS and EPA
reclassifies the area to Serious for the 2012 annual PM2.5
NAAQS.

C. Reasonably Available Control Measures/Reasonably Available Control
Technology

1. Requirements for RACM/RACT
    The general subpart 1 attainment plan requirement for RACM and RACT
is described in CAA section 172(c)(1), which requires 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 provide for attainment of the NAAQS.
    The attainment planning requirements specific to PM2.5
under subpart 4 likewise impose upon states with nonattainment areas
classified as Moderate an obligation to develop attainment plans that
require RACM/RACT on sources of direct PM2.5 and all
PM2.5 plan precursors. CAA section 189(a)(1)(C) requires
that Moderate area PM2.5 SIPs contain provisions to assure
that RACM/RACT are implemented no later than 4 years after designation
of the area. The EPA reads CAA sections 172(c)(1) and 189(a)(1)(C)
together to require that attainment plans for Moderate nonattainment
areas provide for the implementation of RACM and RACT for existing
sources of PM2.5 and those PM2.5 precursors
subject to control in the nonattainment area as expeditiously as
practicable but no later than 4 years after designation.\41\
---------------------------------------------------------------------------

    \41\ This interpretation is consistent with guidance provided in
the General Preamble at 13540.
---------------------------------------------------------------------------

    The PM2.5 SIP Requirements Rule defines RACM 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 plan precursor

emissions from sources in the area.\42\ RACM includes reasonably
available control technology (RACT).'' The EPA has historically defined
RACT as the lowest emission limitation that a particular stationary
source is capable of meeting by the application of control technology
(e.g., devices, systems, process modifications, or other apparatus or
techniques that reduce air pollution) that is reasonably available
considering technological and economic feasibility.\43\
---------------------------------------------------------------------------

    \42\ 40 CFR 51.1000. ``PM2.5 plan precursors'' are
defined as ``those PM2.5 precursors required to be
regulated in the applicable attainment plan and/or NNSR program''
and ``PM2.5 precursors'' are SO2,
NOX, VOC, and ammonia.
    \43\ General Preamble at 13541 and 57 FR 18070, 18073-74 (April
28, 1992).
---------------------------------------------------------------------------

    Under the PM2.5 SIP Requirements Rule, those control
measures that otherwise meet the definition of RACM but ``can only be
implemented in whole or in part during the period beginning 4 years
after the effective date of designation of a nonattainment area and no
later than the end of the sixth calendar year following the effective
date of designation of the area'' must be adopted and implemented by
the state as ``additional reasonable measures.'' \44\
---------------------------------------------------------------------------

    \44\ 40 CFR 51.1000, 51.1009(a)(i)(B), and 51.1009(a)(ii)(B).
---------------------------------------------------------------------------

    States must provide written justification in a SIP submission for
eliminating potential control options from further review on the basis
of technological or economic infeasibility.\45\ An evaluation of
technological feasibility may include consideration of factors such as
a source's process and operating conditions, raw materials, physical
plant layout, and non-air quality and energy impacts (e.g., increased
water pollution, waste disposal, and energy requirements).\46\ An
evaluation of economic feasibility may include consideration of factors
such as cost per ton of pollution reduced (cost-effectiveness), capital
costs, and operating and maintenance costs.\47\ Absent other
indications, the EPA presumes that it is reasonable for similar sources
to bear similar costs of emissions reductions. Economic feasibility of
RACM and RACT is thus largely informed by evidence that other sources
in a source category have in fact applied the control technology,
process change, or measure in question in similar circumstances.\48\
---------------------------------------------------------------------------

    \45\ 40 CFR 51.1009(a)(3).
    \46\ 40 CFR 51.1009(a)(3); see also 57 FR 18070, 18073-74.
    \47\ Id.
    \48\ 57 FR 18070, 18074.
---------------------------------------------------------------------------

    Consistent with these requirements, NSAQMD must implement RACM,
including RACT, for direct PM2.5 emission sources no later
than April 15, 2019, and must implement additional reasonable measures
for these sources no later than December 31, 2021.
    The CAA explicitly provides for the use of economic incentive
programs (EIPs), such as the Portola voluntary wood stove change-out
program, as one tool for states to use to achieve attainment of the
NAAQS.\49\ EIPs use market-based strategies to encourage the reduction
of emissions from stationary, area, and mobile sources in an efficient
manner. The EPA has promulgated regulations for statutory EIPs required
under section 182(g) of the Act and has issued guidance for
discretionary EIPs.\50\ Where a state relies on a discretionary EIP in
a SIP submission, the EPA evaluates the programmatic elements of the
EIP to determine whether the resulting emission reductions are
quantifiable, surplus, enforceable and permanent.\51\ These four
fundamental ``integrity elements,'' which apply to all EIPs and other
incentive/voluntary measures relied on for SIP purposes, are designed
to ensure that such programs and measures satisfy the applicable
requirements of the Act.
---------------------------------------------------------------------------

    \49\ See, e.g., CAA sections 110(a)(2)(A), 172(c)(6), and
183(e)(4).
    \50\ A ``discretionary economic incentive program'' is ``any EIP
submitted to the EPA as an implementation plan revision for purposes
other than to comply with the statutory requirements of sections
182(g)(3), 182(g)(5), 187(d)(3), or 187(g) of the Act.'' 40 CFR
51.491; see also 59 FR 16690 (April 7, 1994) (codified at 40 CFR
part 51, subpart U) and ``Improving Air Quality with Economic
Incentive Programs,'' EPA, January 2001 (``2001 EIP Guidance'').
    \51\ 2001 EIP Guidance, section 4.1.
---------------------------------------------------------------------------

2. RACM/RACT Analysis in the Portola PM2.5 Plan
    The State's RACM and RACT analysis is in section VI.D of the
Portola PM2.5 Plan. The emissions inventory analysis,
conducted as part of the RACT analysis, confirmed that no major
stationary sources of direct PM2.5 or any PM2.5
precursor are located in the Portola PM2.5 nonattainment
area. As discussed above in section IV.C, the State provided a
demonstration that PM2.5 precursor emissions do not
contribute significantly to ambient PM2.5 levels that exceed
the standards in the area. Therefore, the Portola PM2.5 Plan
contains a RACM demonstration addressing only sources of direct
PM2.5.
3. Primary Sources of PM2.5 in the Nonattainment Area
    PM2.5 concentrations in the Portola PM2.5
nonattainment area are dominated by direct PM2.5 emissions
from residential wood burning. Chapter II of the Plan documents the
State and District's bases for concluding that wood burning is the
dominant source of PM2.5 throughout the nonattainment area.
The documentation includes seasonal and diurnal patterns in
PM2.5 concentrations, chemical composition data, PMF
modeling, and statistical correlations between PM2.5 mass
and levoglucosan (a wood burning tracer). The PMF model estimated that
76% of ambient PM2.5 on an annual basis is from wood
burning. Burning of garbage in stoves, fireplaces, and in open burn
piles contributes another 2.5% of annual PM2.5 levels.
4. RACM Measures
    Table 2 lists the RACM measures in the Portola PM2.5
Plan. We discuss each of these measures in detail further below.

                          Table 2--Summary of RACM in Portola PM2.5 Nonattainment Area
----------------------------------------------------------------------------------------------------------------
                                        Direct PM2.5 emission
               Measure                     reductions (tpd)         Scheduled action       Implementation year

----------------------------------------------------------------------------------------------------------------
Voluntary Wood Stove Change-out        0.062 \a\..............  2016...................  2016-2020.
 Program with Enforceable Commitment.
City of Portola Wood Stove and         Not estimated \b\......  2016...................  2021.
 Fireplace Ordinance Mandatory Wood
 Burning Curtailment.
Other Provisions in City of Portola    Not estimated \d\......  2016...................  2016.
 Wood Stove and Fireplace Ordinance
 \c\.
Open Burning Requirements (NSAQMD      Not estimated \e\......  2019...................  2019.
 Rules 300-317).
CARB Mobile Source Programs..........  0.006..................  Ongoing................  Ongoing.
Opacity Rule (NSAQMD Rule 202).......  Not estimated..........  Ongoing................  Ongoing.

Educational Campaign.................  Not estimated \f\......  Ongoing................  Ongoing.
Voluntary Wood Burning Curtailment     Not estimated \f\......  2016...................  2017.
 Program (``Clear the Air; Check
 Before You Light'').
----------------------------------------------------------------------------------------------------------------
\a\ The reductions from the wood stove change-out program are based on the average of the cumulative annual
  emission reductions from 2019-2021 (i.e., 0.045 tpd in 2019, 0.065 tpd in 2020, and 0.077 tpd in 2021).
\b\ Additional reductions not calculated because a variety of factors affect the amount of any potential
  reductions still available after implementation of change-out program (e.g., number of remaining uncertified
  wood stoves within City of Portola; whether the 30 [mu]g/m\3\ air quality threshold is triggered to implement
  the curtailment; and enforcement of the curtailment).
\c\ Additional reductions from the other provisions in the Ordinance and the distribution of 20 moisture meters
  per year are uncertain (e.g., reductions from prohibition on burning unseasoned wood) and/or overlap with
  reductions from the change-out program. To avoid double counting of reductions from the Ordinance and the
  change-out programs, no additional reductions from the Ordinance are relied on for attainment.
\d\ Other provisions that apply in the Ordinance include, for example, prohibiting: Installation of an
  uncertified wood burning device, unqualified fireplace, or uncertified fireplace in new construction or
  remodel; more than one certified wood burning heater per dwelling unit in new construction; a wood burning
  device as the sole source of heat in new construction; installation of an outdoor wood-burning boiler or
  hydronic heater; uncertified wood burning heater remaining in any property upon change of ownership; burning
  of garbage or unpermitted fuels, including unseasoned wood (less than 20% moisture content) in a wood burning
  devices.
\e\ Additional reductions from strengthening requirements applicable to non-agricultural open burning (e.g.,
  backyard and barrel burning) to be determined at time of anticipated rulemaking in 2019, but because the non-
  agricultural open burning inventory is small, the additional reductions will not advance attainment.
\f\ For RACM, attainment, and RFP, the District is not relying on any reductions from the educational programs
  or the voluntary wood burning curtailment program.
Source: Portola PM2.5 Plan, 37 (Table 4).

a. Voluntary Wood Stove Change-Out Program
    Because ambient PM2.5 in the Portola area is primarily
caused by residential wood burning, CARB and the NSAQMD have chosen to
implement a voluntary wood stove change-out program as the primary RACM
control strategy for the entire Portola PM2.5 nonattainment
area. Appendix L of the Plan details the voluntary wood stove change-
out program. Its implementation began in 2016 and will continue through
2020. See Table 3 below for the phased schedule of changeouts.

                 Table 3--Wood Stove Change-Out Schedule
------------------------------------------------------------------------
                                                 Stove changeouts
                  Year                   -------------------------------
                                             Per year       Cumulative
------------------------------------------------------------------------
2016....................................             100             100
2017....................................             100             200
2018....................................             150             350
2019....................................             150             500
2020....................................             100             600
2021....................................               0             600
2022....................................               0             600
------------------------------------------------------------------------

    The woodstove change-out program is primarily funded by the EPA and
the District. The District has approximately $3 million to fund the
replacement of 600 of the estimated 664 uncertified wood stoves \52\ in
use in the nonattainment area. The District is utilizing $2.48 million
through the EPA's 2015 Targeted Air Shed Grant program \53\ and
$400,000 from H&S Performance (H&S) pursuant to a December 17, 2015
Consent Agreement and Final Order between H&S and the EPA.\54\
Additionally, the District is contributing up to $60,000 from the
Plumas County portion of the District's Assembly Bill 2766 Motor
Vehicle Registration fee surcharge.
---------------------------------------------------------------------------

    \52\ Throughout this notice, we use the term ``uncertified wood
stove'' to refer to a wood heater that is not certified under the
applicable Phase II requirements of the EPA's new source performance
standards (NSPS) promulgated in 1988 for new residential wood
heaters at 40 CFR part 60, subpart AAA, as effective February 26,
1988 (53 FR 5860). In 2015, the EPA revised subpart AAA, Standards
of Performance for New Residential Wood Heaters (``2015 NSPS'') with
an effective date of May 15, 2015, and a sell-through date of
December 31, 2015. See 53 FR 5860 (March 15, 2015). Because the
Voluntary Wood Stove Change-out Program began after December 31,
2015, all new certified wood heaters sold in the Portola
PM2.5 nonattainment area must meet the applicable
requirements in the 2015 NSPS.
    \53\ The Targeted Air Shed grant program is intended to improve
air quality in areas of the US with the highest levels of pollution.
For more information, see https://www.epa.gov/grants/air-grants-and-funding.
    \54\ In the Matter of H&S Performance, LLC, Consent Agreement
and Final Order (docket no. CAA-HQ-2015-8248), entered December 17,
2015. Under this agreement, H&S Performance, LLC agreed to provide
$400,000 to the NSAQMD to replace, retrofit, or upgrade at least 400
inefficient wood-burning appliances.
---------------------------------------------------------------------------

    The change-out program includes specific requirements designed to
achieve quantifiable, surplus, enforceable, and permanent
PM2.5 emission reductions in the entire Portola
PM2.5 nonattainment area. The program requirements ensure,
among other things, that older, dirtier wood stoves currently in
operation in the Portola PM2.5 nonattainment area will be
replaced with EPA-certified wood stoves or other less-polluting
devices. Residents of the City of Portola and low-income residents
living outside the city but within the nonattainment area qualify for
up to $3,500 to replace an uncertified wood burning device with an EPA-
certified wood burning device. The $3,500 covers all or most of the
change-out costs. In an effort to replace the uncertified devices with
the cleanest technology available, the District offers an additional
$1,000 to city residents or low-income residents within the
nonattainment area for every uncertified wood stove replaced with a
pellet, propane, or kerosene device. For all other residents living
outside the City of Portola but within the nonattainment area, the
District offers $1,500 to replace an uncertified wood burning device
with an EPA-certified wood burning device and $3,000 to replace an
uncertified wood burning device with a pellet, propane or kerosene
heating device. An incentive is available within the entire
nonattainment area, but the two-tier funding approach increases the
likelihood of the greatest number of changeouts occurring in the city,
the area with the greatest concentration of people and low-income
residents in the nonattainment area. As of September 30, 2018,
approximately 260 changeouts were completed, and an additional 49
applications were approved for possible future changeouts.\55\
---------------------------------------------------------------------------

    \55\ Portola Monthly Air Quality Update from NSAQMD, September
2018.
---------------------------------------------------------------------------

    The change-out program also includes requirements for participating

contractors/retailers to sign a contract with NSAQMD. Contractors/
retailers must meet licensing, permitting, and certification
requirements. The contract includes specific requirements for the
collection and retention of documents, such as:
    [ssquf] Program tracking form,
    [ssquf] Copy of change-out cost estimate with District approval
signature,
    [ssquf] Photo of uncertified woodstove installed and operational in
home (prior to replacement by certified device),\56\
---------------------------------------------------------------------------

    \56\ The District also developed a memorandum of understanding
with the City of Portola to destroy the replaced stoves. The City
matches the stove with the program tracking number, cuts the stove
in half with a plasma torch, and stores the stove in a locked yard.
The City fills out and signs a verification of destruction form and
submits it to the District. The form contains the tracking number
and photo of the destroyed stove. See Portola PM2.5 Plan,
32.
---------------------------------------------------------------------------

    [ssquf] Photo of certified device installed,
    [ssquf] Copy of building permit,
    [ssquf] Acknowledgement of training form (homeowner/renter), and
    [ssquf] Final invoice.
    The retailer/contractor must also meet the following requirements
for retention of records and providing training to homeowners:
    [ssquf] Accounting records relating to the change-out program must
be retained for five years and made available for possible review by
federal, State and District agencies,
    [ssquf] Encourage homeowners to consider replacing wood appliances
with alternative fuel devices, such as propane, pellet or kerosene, and
    [ssquf] Train homeowners on proper appliance operation and
acceptable fuels to maximize the emission reductions, including a form
signed by homeowners stating that they were trained to properly operate
their new heating device.
    To provide assurance that the voluntary change-out program will
achieve the intended emissions reductions, the District adopted an
enforceable commitment to replace 600 uncertified stoves with cleaner
burning devices by December 31, 2020. The EPA approved this enforceable
commitment into the SIP at 83 FR 13871 (April 2, 2018). The enforceable
commitment obligates the NSAQMD to achieve specific amounts of
PM2.5 emission reductions through implementation of the
woodstove change-out program by specific years, to submit annual
reports to the EPA detailing its implementation of the program and the
projected emission reductions, and to adopt and submit substitute
measures by specific dates if the EPA determines that the woodstove
change-out program will not achieve the necessary emission reductions.
The EPA's Technical Support Document for its April 2, 2018 final action
has more information about the enforceable commitment.
b. City of Portola Wood Stove and Fireplace Ordinance
    On June 22, 2016, the City of Portola adopted Ordinance No. 344,
``An Ordinance of the City of Portola, County of Plumas Amending
Chapter 15.10 of the City of Portola Municipal Code Providing for
Regulation of Wood Stoves and Fireplaces'' (``City Ordinance''). The
City Ordinance is in Appendix M of the Plan. The EPA approved the City
Ordinance into the SIP at 83 FR 9213 (March 5, 2018).
    The City Ordinance includes a mandatory burning curtailment
provision effective January 1, 2021. The mandatory curtailment will
restrict wood burning under specific conditions. If the District
determines that adverse meteorological conditions are expected to
persist and PM2.5 may exceed 30 [mu]g/m\3\ on a given day in
January, February, November, or December, the District will call a ``No
Burn Day.'' When a No Burn Day is called, no person may operate a wood
burning heater, wood burning fireplace, wood-fired fire pit or wood-
fired cookstove within the city limits unless it is an approved and
currently registered EPA-certified wood burning heater.\57\ The
curtailment provision encourages owners of uncertified stoves to
upgrade to certified stoves or risk not being able to use their
uncertified wood burning device on No Burn Days called after January 1,
2021. The curtailment provision does not take effect until January 1,
2021, giving homeowners and renters time to change their stoves to EPA-
certified devices during the five-year implementation of the voluntary
change-out program.
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    \57\ See section 15.10.060 of the City Ordinance. In section
15.10.020 of the City Ordinance, ``wood burning heater'' is defined
as an enclosed wood-burning device capable of and intended for space
heating such as a wood stove, pellet-fueled wood heater, or wood-
burning fireplace insert, and ``EPA-certified'' is defined as any
wood burning heater with a Phase II certification or a more
stringent certification as currently enforced in the NSPS.
---------------------------------------------------------------------------

    The City Ordinance and the District's wood stove change-out program
collectively establish most of the recommended program elements
outlined in the EPA's guidance document entitled ``Strategies for
Reducing Residential Wood Smoke,'' \58\ including:
---------------------------------------------------------------------------

    \58\ EPA, ``Strategies for Reducing Residential Wood Smoke,''
Publication No. EPA-456/B-13-001, revised March 2013.
---------------------------------------------------------------------------

    [ssquf] A wood burning curtailment program (section 15.10.060),
    [ssquf] Requirements to remove uncertified wood burning stoves upon
home resale (section 15.10.040.A),
    [ssquf] Restrictions on wood burning devices in new construction
(section 15.10.030.B),
    [ssquf] Restrictions on the installation of wood burning fireplaces
(sections 15.10.030.A and 15.10.040.B),
    [ssquf] A requirement that all wood burning stoves sold or
transferred within the District meet the EPA's current new source
performance standard certification (section 15.10.030.A),
    [ssquf] A prohibition on the installation of wood fired boilers or
hydronic heaters (sections <IP_ADDRESS>, 15.10.030.A and 15.10.070),
    [ssquf] Requirements regarding wood moisture content (section
15.10.050.A),
    [ssquf] Restrictions on types of materials that may be burned
(seasoned wood, uncolored paper, pellets, and manufactured logs)
(section 15.10.050),
    [ssquf] A wood burning stove change-out program (described above),
and
    [ssquf] Education and outreach programs, including a requirement
for wood stove retailers to distribute educational materials provided
by the District (section 15.10.080).
    Although natural gas is not available in the area, the City
Ordinance does not include any exemption for a residence where an
uncertified wood stove is the sole source of heat. The City Ordinance
is thus more stringent than curtailment provisions implemented by other
air districts, most of which exempt households using wood stoves as a
sole source of heat from curtailment requirements.\59\
---------------------------------------------------------------------------

    \59\ See e.g., South Coast Air Quality Management District Rule
445 (amended May 3, 2013), paragraph (f)(7)(A), and Sacramento
Metropolitan Air Quality Management District Rule 421 (amended
September 24, 2009), paragraph 112.
---------------------------------------------------------------------------

    The District considered expanding the requirements of the City
Ordinance to the entire nonattainment area but determined that this was
not feasible because the District did not have sufficient funding to
offer incentives to cover the full cost of changeouts outside of the
City of Portola. Some residents living outside of the city limits may
not have sufficient resources to changeout their stoves. For these
residents, the wood burning prohibition in the City Ordinance could
cause unintended health risks if their sole source of heat is an
uncertified wood stove, and they were prohibited from using it. In the
future, expanding application of the City Ordinance beyond city limits
will be contingent upon availability of more generous incentive funds
for people residing outside the city limits. The

Plan states that if additional funding becomes available in the future,
the District will offer more generous incentives to residents living
outside city limits and consider expanding mandatory burning
curtailment to the entire nonattainment area.\60\
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    \60\ Portola PM2.5 Plan, Table 4, 84-85.
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c. Open Burning (NSAQMD Rules 300-317)
    The District enforces open burning requirements in NSAQMD Rules
300--317 that apply to a variety of area sources such as agricultural
burning, forest burning, range improvement, and residences. The
District's smoke management program ensures that open burning occurs on
days with good dispersion to minimize the impact from PM2.5
concentrations. The EPA approved these rules into the SIP at 62 FR
48480 (September 16, 1997) and 64 FR 45170 (August 19, 1999).
    Within the Portola nonattainment area, wood smoke can originate
from open burning or from home heating devices. Residents of this area
occasionally burn yard debris in open piles. Land managers (e.g., U.S.
Forest Service) perform prescribed burns of timber harvest waste to
promote fire safety and maintain forest health. Both residents and land
managers must request a burn permit prior to starting a fire. The
District, in coordination with CARB, makes a declaration of either a
permissive Burn Day or a No Burn Day in the context of open burning
only. It does not apply to wood burning devices and is distinct from
the more stringent No Burn Day program previously described in the City
Ordinance. The District and CARB consider a number of factors in making
no-burn declarations to ensure that smoke from open burning will not
unduly contribute to the ambient PM2.5 mass.\61\
---------------------------------------------------------------------------

    \61\ Id. at 22.
---------------------------------------------------------------------------

    To further reduce PM2.5 emissions during winter, the
Portola PM2.5 Plan contains a commitment by the District to
strengthen its open burning rule in 2019. The District is assessing the
feasibility of green waste collection in the nonattainment area and
will consider whether to adopt open burning requirements similar to
District Rule 318 (``American Valley Burning Restrictions''), which
prohibits the open burning of yard waste and debris or other rubbish
from November 15 to March 15 in a portion of the American Valley
containing Quincy and East Quincy.\62\
---------------------------------------------------------------------------

    \62\ Id. at 36.
---------------------------------------------------------------------------

d. Mobile Source Measures
    Mobile sources account for approximately 3% of the overall direct
PM2.5 emissions inventory in the Portola PM2.5
nonattainment area. The Plan projects that CARB's continued
implementation of adopted mobile source control measures \63\ will
decrease direct PM2.5 emissions by 2021 and provide 7% of
the total reductions needed to attain the 2012 PM2.5 NAAQS.
As part of the State's RACM analysis for the mobile source control
program, described on pages 86-90 of the Portola PM2.5 Plan,
CARB concludes that in light of the comprehensiveness and stringency of
its mobile source program, all RACM under CARB's jurisdiction are
already being implemented.
---------------------------------------------------------------------------

    \63\ CARB has unique authority under CAA section 209 (subject to
a waiver or authorization by the EPA) to adopt and implement new
emissions standards for many categories of vehicles and engines.
CARB has adopted standards and other requirements related to the
control of emissions from numerous types of new and in-use on-road
and off-road vehicles and engines, such as trucks, buses,
motorcycles, passenger cars, off-road engines (gasoline and diesel-
powered), off-road diesel fueled fleets, portable equipment, and
marine engines. Generally, these regulations have been submitted and
approved as revisions to the California SIP. See, e.g., 77 FR 20308
(April 4, 2012), 81 FR 39424 (June 16, 2016), 82 FR 14446 (March 21,
2017), and 83 FR 23232 (May 18, 2018).
---------------------------------------------------------------------------

e. Visible Emissions (NSAQMD Rule 202)
    Rule 202 limits visible emissions (e.g., particulates) and is
enforced by NSAQMD. The EPA approved this rule into the SIP at 62 FR
48480 (September 16, 1997). Enforcement of Rule 202 will help identify
households with highly visible emissions that may still be using
uncertified wood stoves and possibly eligible for the change-out
program. Rule 202 prohibits any person from discharging into the
atmosphere any air contaminant for more than 3 minutes in any hour that
is as dark as, or darker in shade than, that designated as No. 1 on the
Ringelmann Chart or ``of such opacity as to obscure an observer's view
to a degree equal to or greater than does smoke.'' \64\
---------------------------------------------------------------------------

    \64\ NSAQMD Rule 202, ``Visible Emissions'' (adopted September
11, 1991).
---------------------------------------------------------------------------

f. Educational Campaign
    The District is developing other voluntary measures to reduce the
impact of wood smoke on PM2.5. The District is conducting an
aggressive outreach and educational campaign to help residents
understand the benefits of changing from an old wood stove to a cleaner
home heating device and the importance of clean burning. The District
worked closely with the City of Portola and enlisted outreach partners
such as the local hardware and grocery store, post office, library,
senior community center, and schools to assist in the distribution of
educational materials and advertise the change-out program. In
addition, the Ordinance includes a requirement that retailers and
contractors provide educational materials with the sale of a wood-
burning device.\65\
---------------------------------------------------------------------------

    \65\ Portola PM2.5 Plan, 34-35.
---------------------------------------------------------------------------

g. Voluntary Wood Burning Curtailment Program
    On November 1, 2017, the District began implementing ``Clear the
Air; Check Before You Light,'' a voluntary wood burning curtailment
program that runs during the peak wood-burning period (i.e., November 1
through February 28) in the Portola nonattainment area. When conditions
exist for potentially poor air quality, the District will issue an air
quality advisory to notify the public. When an advisory is triggered
the District will recommend avoiding the use of any wood burning device
(including wood stoves, fireplaces, fire pits and cook stoves) to help
reduce potential health impacts and possibly prevent an exceedance of
federal/state air pollution standards. Use of alternative sources of
heat such as electricity, propane or kerosene, are encouraged when an
advisory is announced.\66\
---------------------------------------------------------------------------

    \66\ NSAQMD Press Release dated October 25, 2017, Greater
Portola Area Wintertime Advisory Program in Effect.
---------------------------------------------------------------------------

5. The EPA's Evaluation and Proposed Action
    As part of the EPA's March 5, 2018, final action approving the City
Ordinance into the SIP, the EPA considered whether the City Ordinance
includes all technologically and economically feasible measures for
wood burning devices. We compared the provisions in the City Ordinance
with other wood burning rules and with the recommendations in the EPA's
guidance document entitled ``Strategies for Reducing Residential Wood
Smoke.'' \67\ Based on this evaluation, we concluded that the City
Ordinance and the District's wood stove change-out program collectively
implement RACM and additional reasonable measures for residential wood
burning devices in the Portola nonattainment area.\68\
---------------------------------------------------------------------------

    \67\ EPA, ``Strategies for Reducing Residential Wood Smoke,''
Publication No. EPA-456/B-13-001, revised March 2013, and EPA,
``Residential Wood Combustion Summary of Measures--DRAFT,'' January
2016.
    \68\ 83 FR 9213 (November 3, 2017) and EPA, Region IX Air
Division, ``Technical Support Document for the EPA's Rulemaking for
the California State Implementation Plan, Northern Sierra Air
Quality Management District, City of Portola Ordinance 344, Wood
Stove and Fireplace Ordinance,'' July 2017.

---------------------------------------------------------------------------

    We note that the curtailment provisions of the City Ordinance do
not take effect until 2021. Given that uncertified wood stoves are
currently the primary source of heat for many residents in Portola, we
do not believe it is reasonable to require implementation of a
mandatory curtailment program prior to implementation of the District's
five-year wood stove change-out program, which provides funding for the
replacement of 600 uncertified wood stoves between 2016 and 2020. After
these incentive funds are disbursed, however, implementation of a
mandatory curtailment program in the Portola nonattainment area is
feasible. We propose to find that the District's enforceable
commitments concerning implementation of the wood stove change-out
program and related monitoring and reporting commitments implement RACM
for the control of PM2.5 emissions from residential wood
burning in the Portola area. Because the curtailment provision in the
City Ordinance otherwise meets the definition of RACM but is
implemented during the period beginning 4 years after the area's
designation as nonattainment and before the attainment date, we
consider it an additional reasonable measure for purposes of attaining
the 2012 PM2.5 NAAQS.
    Under the CAA, the EPA is charged with establishing national
emissions limits for mobile sources. States are generally preempted
from establishing such limits except for California, which can
establish these limits subject to EPA waiver or authorization under CAA
section 209 (referred to herein as ``waiver measures''). Over the
years, the EPA has issued waivers (for on-road vehicles and engines
measures) or authorizations (for non-road vehicle and engine measures)
for many mobile source regulations adopted by CARB.
    In the past, the EPA allowed California to take into account
emissions reductions from waiver measures, notwithstanding the fact
that these regulations had not been approved as part of the California
SIP. However, in response to the decision by the United States Court of
Appeals for the Ninth Circuit in Committee for a Better Arvin v.
EPA,\69\ the EPA approved waiver measures as revisions to the
California SIP.\70\ CARB's mobile source program extends beyond
regulations that are subject to the waiver or authorization process set
forth in CAA section 209 to include standards and other requirements to
control emissions from in-use heavy duty trucks and buses, gasoline and
diesel fuel specifications, and many other types of mobile sources.
Generally, these regulations have been submitted and approved as
revisions to the California SIP.\71\ The Portola PM2.5 Plan
relies to a very small extent on emissions reductions from
implementation of the waiver measures through the use of emissions
models such as EMFAC2014.
---------------------------------------------------------------------------

    \69\ Committee for a Better Arvin v. EPA, 786 F.3d 1169 (9th
Cir. 2015) (``Arvin''). In Arvin, the Ninth Circuit concluded that
CAA section 110(a)(2)(A) requires that all state and local control
measures on which SIPs rely to attain the NAAQS, including
California waiver measures, be included in the SIP and thereby
subject to enforcement by the EPA and the general public. This
decision struck down the EPA's longstanding practice of approving
California plans that rely on emissions reductions from waiver
measures notwithstanding their lack of approval as part of the SIP.
    \70\ See, e.g., 81 FR 39424 (June 16, 2016), 82 FR 14447 (March
21, 2017), and 83 FR 23232 (May 18, 2018).
    \71\ See, e.g., the EPA's approval of standards and other
requirements to control emissions from in-use heavy-duty diesel-
powered trucks, at 77 FR 20308 (April 4, 2012), revisions to the
California on-road reformulated gasoline and diesel fuel regulations
at 75 FR 26653 (May 12, 2010), and revisions to the California motor
vehicle I/M program at 75 FR 38023 (July 1, 2010).
---------------------------------------------------------------------------

    The EPA is proposing to find that the District's enforceable
commitment to implement the voluntary wood stove change-out program,
the City Ordinance, CARB's mobile source program, the District's
commitment to strengthen its open burning measure, and other controls
on sources in the nonattainment area together implement all RACM and
RACT for the control of direct PM2.5 in the Portola
nonattainment area. This collective set of PM2.5 control
requirements, particularly with respect to homes where wood-burning is
the sole source of heat, is at least as stringent as analogous measures
implemented in other Moderate PM2.5 nonattainment areas with
similar geography and demographics. Accordingly, the EPA is proposing
to approve the PM2.5 RACM demonstration in the Portola
PM2.5 Plan as meeting the requirements of CAA sections
172(c)(1) and 189(a)(1)(C) and 40 CFR 51.1009.

D. Major Stationary Source Control Requirements Under CAA Section
189(e)

    Section 189(e) of the Act specifically requires that the control
requirements applicable to major stationary sources of direct
PM2.5 also apply to major stationary sources of
PM2.5 precursors, except where the Administrator determines
that such sources do not contribute significantly to PM2.5
levels that exceed the standards in the area.\72\ The control
requirements applicable to major stationary sources of direct
PM2.5 in a Moderate PM2.5 nonattainment area
include, at minimum, the requirements of a NNSR permit program meeting
the requirements of CAA sections 172(c)(5) and 189(a)(1)(A). In the
PM2.5 SIP Requirements Rule, we established a deadline for
states to submit NNSR plan revisions to implement the PM2.5
NAAQS 18 months after an area is initially designated and classified as
a Moderate nonattainment area.\73\ On September 6, 2016, California
submitted the required NNSR SIP revisions. We are not proposing any
action on the NNSR submittal at this time and will address these
requirements in a separate rulemaking.
---------------------------------------------------------------------------

    \72\ General Preamble, 13539 and 13541-42. There are no major
stationary sources (existing or anticipated) of direct
PM2.5 or PM2.5 precursors in the Portola
PM2.5 nonattainment area.
    \73\ 81 FR 58528 at 58010 (August 24, 2016).
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E. Air Quality Modeling

1. Requirements for Air Quality Modeling
    Section 189(a)(1)(B) of the CAA requires that a plan for a Moderate
PM2.5 nonattainment area include a demonstration (including
air quality modeling) that the plan will provide for attainment by the
applicable attainment date, or a demonstration that attainment by such
date is impracticable. An attainment demonstration must show that the
control measures in the plan are sufficient for attainment of the NAAQS
by the attainment date. The attainment demonstration predicts future
ambient concentrations for comparison to the NAAQS, making use of
available information on ambient concentrations, meteorology, and
current and projected emissions inventories, including the effect of
control measures in the plan. This information is typically used in
conjunction with a computer model of the atmosphere.
    The EPA has provided additional modeling requirements and guidance
for modeling analyses in the ``Guideline on Air Quality Models''
(``Guideline'').\74\ For areas where emissions are dominated by primary
PM10 or PM2.5 emitted by many small dispersed
sources, such as fugitive dust or residential wood burning, states have
historically used a ``rollback model'' to evaluate the impacts of
emissions on ambient air quality. EPA recently

approved rollback-based attainment demonstrations in the wood smoke-
dominated Klamath Falls and Oakridge-Westfir PM2.5
nonattainment areas in Oregon.\75\ In a simple rollback model, the
monitored ambient concentration (excluding any unchanging background
concentration) is assumed to be proportional to emissions; when
emissions are reduced by a given percentage, the concentration is
assumed to scale or ``roll back'' by the same percentage. A variant is
``proportional rollback,'' in which rollback is applied to each
emission source category individually, then summed in proportion to
their ambient contributions. The proportions, or source apportionment,
can be estimated using chemically speciated PM2.5
measurements. This can be done with a receptor model such as the
Chemical Mass Balance model or the PMF model, which compute the source
category contributions that are the best statistical fit to the
measured chemical species concentrations, given measured or estimated
source species profiles.
---------------------------------------------------------------------------

    \74\ 40 CFR part 51 Appendix W, ``Guideline on Air Quality
Models,'' 82 FR 5182, January 17, 2017; available at https://www.epa.gov/scram/clean-air-act-permit-modeling-guidance.
    \75\ 81 FR 36176 (June 6, 2016), docket EPA-R10-OAR-2013-0005
for Klamath Falls; and 83 FR 5537 (February 8, 2018), docket EPA-
R10-OAR-2017-0051 for Oakridge-Westfir.
---------------------------------------------------------------------------

2. Modeling in the Portola PM2.5 Plan
    The attainment demonstration, described in section V of the Plan,
is based on proportional rollback, with source category proportions
(source apportionment) determined using the PMF receptor model. Section
V of the Plan describe the concentration starting point for the
rollback, background concentrations, the mapping of ambient
PM2.5 components to PM2.5 emission categories,
and the rollback calculation procedure. In addition to a ``Traditional
Rollback,'' the Plan also provides an ``Alternative Rollback,'' which
is based on a more precise accounting of the impacts of various wood
stove types.
    The concentration starting point for rollback is typically a base
year design value concentration that corresponds to the base year
emissions. Instead of using the 2013 design value for the base year,
the Plan used 13.9 [micro]g/m\3\, the average of the design values from
2013, 2014, and 2015. Because a single design value is a three-year
average, the Plan's procedure gives a five-year weighted average
centered on 2013, using concentrations from 2011-2015. This was done to
reduce the effect of year-to-year variability, and to avoid basing the
attainment demonstration solely on the unusually warm, dry years of
2011-2013.
    In rollback, the area's emissions are used to scale only the
portion of the concentration due to sources in the nonattainment area,
excluding background concentrations. CARB chose speciated
PM2.5 concentrations from Bliss State Park next to Lake
Tahoe in the Plan as background concentrations that would occur in the
airshed in the absence of local anthropogenic emissions.
    The State determined the contributions of emission source
categories to ambient PM2.5 using the PMF receptor model,
described in Plan Appendix A. PMF was applied to 2011-2014 speciated
PM2.5 data for 15 chemical species. PMF determines source
species profiles and source contribution levels that best fit the full
set of data. The result was a source apportionment with estimates for
the ambient contributions of six source categories: Wood burning,
refuse burning, mobile, airborne soil, secondary nitrate, secondary
sulfate.
    The contributions of these source categories to the rollback base
year PM2.5 concentration are shown in the Figure 9 pie chart
in the Plan, ``2011-2015 Annual Average PM2.5 Source
Contribution.'' Wood burning contributed by far the largest amount,
76.1%; mobile sources contributed 7.6%; airborne soil 3.9%; and refuse
burning 2.5%. Secondary PM2.5 in the form of ammonium
nitrate and ammonium sulfate contributed 5.1% and 4.8%, respectively,
of ambient PM2.5 concentrations. Figure 11 in the Plan shows
the strong correlation between concentrations of PM2.5 and
of levoglucosan, a marker for wood combustion.\76\ This correlation
corroborates the significant contribution of wood burning to Portola's
ambient PM2.5 levels.
---------------------------------------------------------------------------

    \76\ Levoglucosan is an organic compound formed from the
pyrolysis of carbohydrates, such as starch and cellulose, the key
component of wood. As a result, levoglucosan is often used as a
chemical tracer for biomass burning in atmospheric chemistry
studies, particularly with respect to airborne particulate matter.
Jordan, T., Seen, A., Jacobsen, G., 2006, ``Levoglucosan as an
atmospheric tracer for woodsmoke,'' Atmospheric Environment, 40
(27): 5316-5321.
---------------------------------------------------------------------------

    Table 12 in the Portola PM2.5 Plan shows the State's
rollback calculation, in which the percent changes in the 2013
emissions of the inventory source categories are applied to their
respective 2013 base year ambient contributions (excluding background).
The main emissions change between base year and future emissions is for
wood burning, reflecting the effect of the wood stove change-out
program. For this source category, the State calculated emission
reductions due to the wood stove change-out program during that period
for each of the years from 2017 to 2021 using the EPA's Burn Wise
Emission Calculator.\77\ CARB applied reductions in tpd to the baseline
emission inventory projections for annual average direct
PM2.5 emissions from residential wood burning in Table 8 of
Appendix B in the Plan.
---------------------------------------------------------------------------

    \77\ Portola PM2.5 Plan Appendix E, Figure 1 and
Table 2. The Burn Wise Emission Calculator is available at https://www.epa.gov/burnwise/burn-wise-additional-resources.
---------------------------------------------------------------------------

    The Plan includes future year contributions from 2017 to 2021 for
each source category and a total concentration for each year. Only the
wood burning emissions differed for each of these years; emissions from
other categories reflected their 2021 values. CARB then averaged the
predicted concentrations for the 2019-2021 period to arrive at a 2021
predicted design value. The State's procedure of averaging projected
concentrations for the three individual years 2019, 2020, and 2021 is
similar to the procedure used for computing the 2021 monitored design
value. The result of the rollback was a predicted 2021 PM2.5
annual design value of 12.03 [micro]g/m\3\; with the rounding to one
digit prescribed by 40 CFR 50 App. N, section 4.3, this meets the 12.0
[micro]g/m\3\ NAAQS.
    Section V.F. of the Plan provided an ``Alternative Rollback'' model
that more precisely quantified the effect of the stove change-out
program on wood burning emissions. For this rollback model, all other
source category emissions and their ambient contributions were assumed
to remain at their base year 2013 levels. CARB calculated wood stove
emissions and contributions separately for new certified stoves and
uncertified stoves. This approach used the individual heating
efficiency and emissions factors for these sources from the EPA's Burn
Wise Emission Calculator and accounted for the number of each type of
stove and the number of stove changeouts expected to occur in 2019,
2020, and 2021. CARB applied the fractional changes in emissions for
these years to the wood burning portion of the 5-year weighted 13.9
[micro]g/m\3\ design value, and the three years' results averaged to
arrive at a 2021 design value of 11.1 [micro]g/m\3\, which meets the
12.0 [micro]g/m\3\ NAAQS.
3. The EPA's Evaluation and Proposed Action
    The EPA evaluated the State's choice of model for the attainment
demonstration, as well as how the State applied the model, in terms of

concentration starting point, background concentrations, mapping of
emissions to concentrations, and the calculations used. The choice of
an appropriate model for the District's attainment demonstration was
informed by particular circumstances in the Portola PM2.5
nonattainment area, most notably the dominance of primary
PM2.5 in ambient concentrations, the dispersed nature of the
many small area sources responsible for it, and the relatively small
fraction that is composed of secondary particulate matter. As discussed
in the Plan, wood burning emissions of organic carbon and elemental
carbon contribute 76% and 8%, respectively, of annual PM2.5
concentrations in the Portola area.\78\ Based on examination of
meteorology, PM2.5 emissions data and ambient
PM2.5 data, the Plan provides a well-supported demonstration
that residential wood burning is the dominant contributor to the
PM2.5 air quality problem in the Portola area. The key
assumption in a rollback analysis, i.e., that ambient concentrations
are proportional to emissions, is true for these primary
PM2.5 emissions. The EPA modeling guidance cited above does
not mention rollback for attainment demonstrations but also does not
fully address situations like that in the Portola area, where the
dominant contributor to ambient PM2.5 is primary
PM2.5 from many small area sources. Given that the key
contributor to the air quality problem in the Portola area is already
understood, neither photochemical grid models nor dispersion models
would provide much information that is not already available from the
rollback model. The EPA agrees that the use of rollback analysis under
these facts and circumstances is consistent with EPA guidance and is
appropriate for the Portola attainment demonstration and meets the
Clean Air Act requirement for air quality modeling.
---------------------------------------------------------------------------

    \78\ Portola PM2.5 Plan, 20 (Figure 9, 2011-2015
Annual Average PM2.5 Source Contribution).
---------------------------------------------------------------------------

    In addition, the EPA agrees that the Plan identifies an appropriate
starting point concentration for the rollback model. The use of a five-
year weighted average for the design value is not standard for
rollback, but is consistent with the EPA's recommendation for the
starting point of photochemical modeling attainment demonstrations. The
Plan contains a reasonable justification for using a longer period to
determine the starting point for the design value, based on the
variable meteorology of the 2011-2015 period; the chosen procedure thus
yields a more representative concentration that is appropriate for the
rollback attainment demonstration. It makes for a more robust
attainment demonstration that is not overly dependent on meteorological
conditions in any one particular year.
    The Plan contains convincing arguments for the State's selection of
Bliss State Park as the source of background concentrations. The EPA
agrees that the Plan's estimates for background concentrations are
appropriate. The source attribution using PMF carried out for the Plan
provides a good basis for the rollback model. The States also used
several conservative assumptions, such as keeping certain ambient
components constant instead of declining with emissions, so that the
final concentration result is likely higher than would be expected with
a more precise accounting.
    As noted above, the Plan used the average of projections for the
individual years 2019, 2020, and 2021 for the future year projection.
In comparison with projecting just the single attainment year emissions
and concentration, the approach used by the State is conservatively
high, because the 2019 and 2020 projections do not account for all of
the emission reductions from stove changeouts that will occur by the
2021 attainment year.\79\
---------------------------------------------------------------------------

    \79\ The attainment demonstration need only show that emissions
in the attainment year and the resulting projected concentration are
consistent with attainment of the NAAQS; it does not need to show
that the projected three-year design value meets the NAAQS. Future
emissions need only be projected to the attainment year itself. See
EPA, Office of Air Quality Planning and Standards, ``Modeling
Guidance for Demonstrating Attainment of Air Quality Goals for
Ozone, PM2.5, and Regional Haze,'' December 2014 Draft,
17 (section 2.3.2, Future Year Selection); available at https://www.epa.gov/scram/state-implementation-plan-sip-attainment-demonstration-guidance.
---------------------------------------------------------------------------

    The Plan also provides a second rollback model, termed
``Alternative Rollback.'' A key difference between the two rollback
approaches is that the ``Alternative'' rollback relies more completely
on the emission methodology for the residential wood burning category
in the Burn Wise Emission Calculator. For both rollback approaches, the
wood stove change-out program was by far the greatest source of
emission and concentration reductions. The approaches relied on PMF
source apportionment for the ambient effect of reductions, and they
accounted for both the PM2.5 reductions per amount of wood
burned in certified stoves and for the lower amount of wood burned from
their increased burn efficiency. The ``Alternative'' rollback
corroborated the results of the ``Traditional'' rollback model and
provides additional confidence in the attainment demonstration.
    The EPA finds that the State correctly implemented the rollback
model in a reasonable way, used an appropriate mapping of ambient
PM2.5 components to emission inventory categories, and
incorporated an appropriate degree of conservatism. For these reasons,
the EPA finds that the rollback modeling in the Plan is adequate for
purposes of supporting the Portola attainment demonstration for the
2012 annual PM2.5 NAAQS.

F. Attainment Demonstration

1. Requirements for Attainment Demonstrations
    CAA section 189(a)(1)(B) requires that each state in which all or
part of a Moderate PM2.5 nonattainment area is located
submit an attainment plan that includes, among other things, either a
demonstration (including air quality modeling) that the plan will
provide for attainment by the applicable attainment date or a
demonstration that attainment by such date is impracticable. In
addition, CAA section 172(c)(1) generally requires, for each
nonattainment area, a plan that provides for the implementation of all
RACM and RACT as expeditiously as practicable and provides for
attainment of the NAAQS. The EPA interprets these two provisions
together to require that an attainment demonstration for a Moderate
PM2.5 nonattainment area meet the following criteria:
    (1) The attainment demonstration must show the projected attainment
date for the Moderate nonattainment area that is as expeditious as
practicable;
    (2) The attainment demonstration must meet the requirements of 40
CFR part 51, appendix W and must include inventory data, modeling
results, and emission reduction analyses on which the state has based
its projected attainment date;
    (3) The base year for the emissions inventory required for the
attainment demonstration must be one of the 3 years used for
designations or another technically appropriate inventory year if
justified by the state in the plan submission; and
    (4) The control strategies modeled as part of the attainment
demonstration must be consistent with the control strategy requirements
under 40 CFR 51.1009(a), including the requirements for RACM/RACT and
additional reasonable measures.\80\
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    \80\ 40 CFR 51.1011(a).

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    In addition, the attainment demonstration must provide for the
implementation of all control measures needed for attainment as
expeditiously as practicable and no later than the beginning of the
year containing the applicable attainment date.\81\
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    \81\ Id.
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    Under longstanding guidance, the EPA has recommended presumptive
limits on the amounts of emission reductions from voluntary and other
nontraditional measures that may be credited in an attainment plan.
Specifically, for voluntary stationary and area source measures, the
EPA has identified a presumptive limit of 6% of the total amount of
emission reductions required for RFP, attainment, or maintenance
demonstration purposes.\82\ The EPA may, however, approve measures for
SIP credit in amounts exceeding the presumptive limits ``where a clear
and convincing justification is made by the State as to why a higher
limit should apply in [its] case.'' \83\
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    \82\ See, e.g., EPA, Office of Air Quality Planning and
Standards, ``Incorporating Emerging and Voluntary Measure in a State
Implementation Plan (SIP),'' October 4, 2004 (``2004 Emerging and
Voluntary Measures Guidance''), 9; EPA, Office of Air Quality
Planning and Standards and Office of Transportation and Air Quality,
``Guidance on Incorporating Bundled Measures in a State
Implementation Plan,'' August 16, 2005 (``2005 Bundled Measures
Guidance''), 8; and EPA, Office of Air Quality Planning and
Standards, ``Guidance for Quantifying and Using Emission Reductions
from Voluntary Woodstove Changeout Programs in State Implementation
Plans,'' EPA-456/B-06-001, January 2006 (``2006 Woodstove
Guidance''), 4.
    \83\ See, e.g., 2004 Emerging and Voluntary Measures Guidance,
9; 2005 Bundled Measures Guidance, 8, n. 6, and 2006 Woodstove
Guidance, 4.
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    We discuss each of these requirements and recommendations for
attainment demonstrations below.

2. Attainment Demonstration in the Portola PM2.5 Plan

    Table 4 shows the relationship between the 2013 base year inventory
and the 2021 attainment year inventory before and after the wood stove
change-out program. The changes to the inventory reflect a 17%
reduction in the direct PM2.5 emissions inventory is needed
to demonstrate attainment by December 31, 2021.

              Table 4--Summary of Attainment Demonstration
------------------------------------------------------------------------
                                                           Direct PM2.5
                        Category                               (tpd)

------------------------------------------------------------------------
a. 2013 Baseline Emissions..............................           0.490
b. Projected 2021 Emissions without Change-out Program             0.486
 \a\....................................................
c. Reductions from Wood Stove Change-out Program \b\....           0.062
d. Attainment Year Emission Inventory = Projected 2021             0.424
 Emissions (b) minus Reductions from Wood Stove Change-
 out Program (c)........................................
------------------------------------------------------------------------
\a\ Mobile source reductions of 0.006 tpd from previously adopted
  measures credited in projected 2021 emission inventory. See Table 8 in
  Appendix B of Portola PM2.5 Plan.
\b\ The average reduction for the 2019-2021 time frame is 0.062 tpd.
  Source: Portola PM2.5 Plan, Table 4, 37.

    Traditional rollback analysis as described in section IV.B. of this
proposed rule indicates that direct PM2.5 reductions from
the woodstove change-out program (i.e., 0.062 tpd average for 2019-2021
as used in the rollback) and CARB's mobile source program (i.e., 0.006
tpd) result in a predicted 2021 design value of 12.03 [micro]g/m\3\ and
is adequate for the State to demonstrate that the Portola area will
attain the 2012 annual PM2.5 standards by the outermost
statutory attainment date as a Moderate nonattainment area of December
31, 2021.\84\ Table 5 below shows the projected cumulative impact of
the change-out program on emission reductions and design values. The
cumulative reductions and design value calculations are offset by one
year to allow for full deployment of stove changeouts in a prior year.
Because the bulk of the changeouts presumably occur during the late
spring, summer, and early fall, the October-December period of a given
year would likely see the greatest air quality benefits from that
year's changeouts, but the January-March period would not. The State's
calculations result in a conservative estimate of the benefits of the
wood stove change-out program because the State is only taking credit
for changeouts that have been in effect for a full year. Thus, the
projected benefit of changing out 600 stoves will not be fully
reflected in the design value until the 2023 design value, which will
include 2021, 2022, and 2023, the first period of three consecutive
years with the 600 new certified devices in operation. The Portola
PM2.5 Plan also includes an alternative rollback modeling
demonstration that results in a 2021 DV of 11.1 [mu]g/m\3\. The
alternative rollback is described in section IV.B. of this proposed
rule and in section V.F. of the Plan.

 Table 5--Relationship Between Cumulative Stove Changeouts, Reductions, and Design Values From Rollback Analysis
----------------------------------------------------------------------------------------------------------------
                                                                                Cumulative
                                                                                direct PM
                                                         Cumulative  stove    reductions in
                                         Stove  change-      changeouts          rollback       Annual  average
                  Year                        outs       credited  towards       analysis       DV  ([mu]g/m\3\)
                                                             attainment     credited  towards
                                                                                attainment
                                                                                (tpd)
----------------------------------------------------------------------------------------------------------------
2016...................................             100                  0                  0    Not calculated.
2017...................................             100                100               .013             13.22.
2018...................................             150                200               .026             12.91.
2019...................................             150                350               .045             12.45.

2020...................................             100                500               .065             11.97.
2021...................................               0                600               .077             11.68.
Projected 2021 DV (average of 2019-      ..............  .................  .................             12.03.
 2021).................................
----------------------------------------------------------------------------------------------------------------
Source: Portola PM2.5 Plan, 56-57 (tables 10 and 11).

    The Portola PM2.5 Plan relies on the wood stove change-
out program to achieve 0.077 tpd of PM2.5 emission
reductions in 2021, approximately 93% of the PM2.5
reductions relied upon in the Plan to demonstrate attainment by the
December 31, 2021 attainment date. The remaining 7% of necessary
emission reductions will be achieved through ongoing implementation of
federal emission reduction programs and CARB's mobile source control
program. To justify this extensive reliance on the voluntary wood stove
change-out program for attainment purposes, the Plan: (1) Provides a
detailed description of the clear need for PM2.5 emission
reductions from wood stove changeouts in the Portola area, (2)
describes features of the wood stove program that provide a greater
level of certainty in the quantification of emission reductions than
that normally associated with voluntary programs, and (3) includes a
detailed, enforceable commitment by the District to monitor and report
on program implementation and to submit substitute measures by specific
dates if necessary to remedy any shortfall in required emission
reductions.\85\
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    \85\ EPA, Region IX Air Division, ``Technical Support Document
for EPA's Notice of Proposed Rulemaking for the California State
Implementation Plan, Evaluation of incentive-based emission
reductions relied upon in the Portola Fine Particulate Matter
(PM2.5) Attainment Plan,'' December 2017.
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    The PM2.5 problem in the Portola nonattainment area is
overwhelmingly caused by residential wood smoke. The District estimates
that between 2011 and 2015, residential wood smoke emissions
contributed 76% of annual average PM2.5 concentrations and
86% of daily PM2.5 concentrations on days exceeding 35
[micro]g/m\3\ at the PM2.5 monitor located in the City of
Portola. Other sources contributing to annual average PM2.5
concentrations include refuse burning (2.5%), mobile sources (7.6%),
secondary sulfates (4.8%), secondary nitrates (5.1%), and airborne soil
(3.9%).\86\
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    \86\ Portola PM2.5 Plan, 20.
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    The average daily low temperature from October to March in the
Portola nonattainment area is 21.8 degrees Fahrenheit with an average
of 218 frost days per year, necessitating ample home heating.\87\ CARB
estimates that of 2,458 households in the nonattainment area, 1,401 use
wood burning devices as a primary or secondary heating source. Of those
wood burning devices, 664 are uncertified woodstoves.\88\ The 2011-2015
median household income in the Portola area was 54% that of the state
median and home values were 40% of the state median.\89\ The
unemployment rate for the City of Portola averaged 10.6% during the
2014-2016 time frame.\90\ According to the District, most residents
cannot afford to replace their uncertified wood burning devices without
significant financial assistance.\91\ Natural gas is not an option for
residential heating because it is not available in the Portola
nonattainment area.\92\ While propane and electric options are
available, the abundance of wood in the area (at no or low cost) and
high cost of these alternative forms of residential heat limit their
feasibility as primary heat sources.\93\
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    \87\ Id. at 8-9.
    \88\ Email dated November 29, 2017, from Katarzyna Turkiewicz,
CARB, to Rynda Kay, EPA, RE: questions about the number of wood
stoves in the Portola nonattainment area.
    \89\ U.S. Census, 2011-2015 American Community Survey 5-year
estimate for City of Portola, CA and State of California.
    \90\ Additional information on unemployment rates in Portola is
available at http://www.homefacts.com/unemployment/California/Plumas-County/Portola/96122.html.
    \91\ Portola PM2.5 Plan, 20.
    \92\ Id. at 29.
    \93\ The average residential electricity rate in the City of
Portola is 17.87[cent]/kWh, which is approximately 50% greater than
the national average rate. See Electricity Local at http://www.electricitylocal.com/states/california/portola/.
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    The bowl-shaped topography, cold stagnant winters, and extensive
use of residential wood stoves in the Portola nonattainment area have
caused evening and morning PM2.5 concentrations to peak
during the winter. According to the District, the diurnal and seasonal
pattern of PM2.5 concentrations peaking in the winter
evening and overnight hours further suggests that residential wood
burning is the primary cause of elevated PM2.5
concentrations in the Portola area rather than open burning of
agricultural wastes, forest management, and other burning
activities.\94\ Although the District has implemented many other
control measures for other sources of direct PM2.5 emissions
in the area,\95\ these measures alone are not sufficient to provide for
attainment in the Portola area given the small percentage of the
PM2.5 emissions inventory attributed to these emission
sources.
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    \94\ Portola PM2.5 Plan, 21.
    \95\ See Portola PM2.5 Plan, 81-82, and our
discussion of RACM/RACT and additional reasonable measures in
section IV.D of this proposed rule.
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    The Plan describes a number of features of the wood stove program
that provide a greater level of certainty in the quantification of
emission reductions than that normally associated with voluntary
programs. First, full funding is already secured to entirely fund the
replacement of 600 wood stoves, which the State projects to be
sufficient to provide for attainment of the 2012 annual
PM2.5 NAAQS by the applicable attainment date. Second, the
emission reduction projections are conservative and relatively well
understood compared to other voluntary programs. This is because wood
stove technologies are generally well understood; wood stoves usually
remain in the residence in which they are installed and have a long
useful life; usage is generally predictable due to the fixed size of
the home and heating needs; emission control technology is unlikely to
be

tampered with; education campaigns and training requirements help
ensure proper operation and fuel selection; and conservative emission
factors are used in emission projections. Third, the program
infrastructure is well-established. The State and District's 2017
annual report on the wood stove program shows that as of December 31,
2017, the program had successfully funded the replacement of 196
stoves.\96\ The State and District estimated that replacement of these
196 uncertified stoves achieved 0.031 tpd of PM2.5 emission
reductions, 19% higher than the projected emissions reductions
accounted for in the attainment demonstration, due to the fact that new
stoves were cleaner than assumed in the attainment demonstration.\97\
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    \96\ CARB, ``Portola Wood Stove Change-Out, 2017 Progress
Report, Covering Change-outs Completed Through 12/31/2017'' (``2017
Annual Report''), 3.
    \97\ Id. at 6 and 13-18.
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    Finally, the Plan includes detailed, enforceable commitments by the
District to monitor and report on program implementation in advance of
the attainment date and to submit substitute measures, if necessary, to
remedy any shortfall in required emission reductions. Specifically, the
District has committed to: Implement the necessary number of woodstove
changeouts in accordance with specific program criteria provided in the
SIP submission; to achieve, by identified dates, specific amounts of
PM2.5 emission reductions from projected baseline levels
identified in the Portola PM2.5 Plan; to submit annual
reports to the EPA that identify the calculator used to quantify
emission reductions and describe, among other things, the projects
implemented, actions taken by the State to confirm project compliance,
and any changes to program implementation forms; and to adopt and
submit to the EPA, by specific dates, any substitute measures necessary
to address a shortfall in required emission reductions. These
commitments became federally enforceable under the CAA upon the EPA's
approval of the commitments into the SIP.\98\
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    \98\ 83 FR 13871 (April 2, 2018).
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3. The EPA's Evaluation and Proposed Action
    The EPA has reviewed the emissions inventories, RACM/RACT
demonstration, air quality modeling, and control strategy fully
described in the Portola PM2.5 Plan.
    In summary and as described in section IV.B of this action, the
State used two modeling techniques to demonstrate attainment of the
2012 annual PM2.5 NAAQS in the Portola nonattainment area.
First, the State used a traditional rollback model to demonstrate
attainment of the 2012 annual PM2.5 NAAQS. Second, the State
corroborated the results of the traditional rollback model by using an
alternative rollback model to also demonstrate attainment. The results
using the alternative rollback model provide additional confidence in
the attainment demonstration. The EPA accepts these modeling approaches
for the attainment demonstration in the Portola PM2.5 Plan.
    Consistent with the requirements of 40 CFR 51.1011(a), the
attainment demonstration shows the projected attainment date that is as
expeditious as practicable in the Portola area, meets the requirements
of 40 CFR part 51, appendix W, and includes inventory data, modeling
results, and emission reduction analyses on which the State has based
its projected attainment date. In addition, the base year for the
emissions inventory used in the attainment demonstration, 2013, is one
of the three years used for designation of the Portola area as a
nonattainment area \99\ and the control strategies modeled as part of
the attainment demonstration are consistent with the control strategy
requirements under 40 CFR 51.1009(a), including the requirements for
RACM/RACT and additional reasonable measures.
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    \99\ 80 FR 2206 (January 15, 2015).
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    With respect to the wood stove change-out program, the EPA believes
that the Portola PM2.5 Plan provides a clear and convincing
justification for more extensive reliance on a voluntary incentive
program to achieve emission reductions necessary for attainment than
the EPA normally recommends. First, the District has shown a clear need
for additional reductions from the wood stove program, as additional
regulatory measures for other PM2.5 emission sources in the
area are not sufficient to provide for attainment, and a mandatory
curtailment on use of wood stoves on high-PM2.5 winter days
is not economically feasible for implementation at this time in the
Portola area. Second, the State and District have identified a number
of program features that provide adequate assurance that the wood stove
changeout program will achieve, at minimum, the emission reductions
attributed to it in the attainment demonstration. Third, the District's
SIP-approved enforceable commitment ensures that the EPA and citizens
can hold the District responsible for achieving the emission reductions
attributed to the wood stove change-out program in the attainment
demonstration.
    Finally, the City Ordinance includes a mandatory curtailment of
uncertified stoves on days when the 24-hour average PM2.5
concentration is forecasted to exceed 30 [mu]g/m\3\ that begins January
1, 2021. This clear prohibition on the operation of uncertified wood
stoves on days with higher PM2.5 levels after January 1,
2021, provides additional assurance that projected emission reductions
will occur in time to provide for attainment of the 2012
PM2.5 NAAQS by the December 31, 2021 attainment date.
    For all of these reasons, we propose to approve the attainment
demonstration in the Portola PM2.5 Plan as satisfying the
requirements of sections 189(a)(1)(B) and 172(c)(1) of the CAA and 40
CFR 51.1011(a).

G. Reasonable Further Progress and Quantitative Milestones

1. Requirements for Reasonable Further Progress and Quantitative
Milestones
    CAA section 172(c)(2) states that all nonattainment area plans
shall require reasonable further progress (RFP). In addition, CAA
section 189(c) requires that all PM2.5 nonattainment area
SIPs include quantitative milestones to be achieved every three years
until the area is redesignated to attainment and which demonstrate RFP,
as defined in CAA section 171(1). Section 171(1) defines RFP as ``such
annual incremental reductions in emissions of the relevant air
pollutant as are required by [Part D] or may reasonably be required by
the Administrator for the purpose of ensuring attainment of the
applicable [NAAQS] by the applicable date.'' Neither subpart 1 nor
subpart 4 of part D, title I of the Act requires that a set percentage
of emissions reductions be achieved in any given year for purposes of
satisfying the RFP requirement.
    For purposes of the PM2.5 NAAQS, EPA has interpreted the
RFP requirement to require that nonattainment area plans show annual
incremental emission reductions sufficient to maintain generally linear
progress toward attainment by the applicable deadline.\100\ As
discussed in EPA guidance in the Addendum to the General Preamble
(``Addendum''),\101\ requiring linear progress in reductions of direct
PM2.5 and any individual precursor in a PM2.5
plan may be appropriate in situations where:
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    \100\ Addendum to the General Preamble, 59 FR 41998 (August 16,
1994), 42015.