[Federal Register Volume 83, Number 26 (Wednesday, February 7, 2018)]
[Proposed Rules]
[Pages 5375-5399]
[FR Doc No: 2018-02462]

=======================================================================
-----------------------------------------------------------------------

ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 52

[EPA-R09-OAR-2017-0177; FRL-9974-10-Region 9]

Approval and Promulgation of Air Quality State Implementation
Plans; California; Interstate Transport Requirements for Ozone, Fine
Particulate Matter, and Sulfur Dioxide

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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

SUMMARY: The Environmental Protection Agency (EPA) is proposing to
approve a State Implementation Plan (SIP) submission from the State of
California regarding certain interstate transport requirements of the
Clean Air Act (CAA or ``Act''). This submission addresses the 2008
ozone national ambient air quality standards (NAAQS), the 2006 fine
particulate matter (PM2.5) and 2012 PM2.5 NAAQS,
and the 2010 sulfur dioxide (SO2) NAAQS. The interstate
transport requirements under the CAA consist of several elements; this
proposal pertains only to significant contribution to nonattainment and
interference with maintenance of the NAAQS in other states. We are
taking comments on this proposal and plan to follow with a final
action.

DATES: Any comments must arrive by March 9, 2018.

ADDRESSES: Submit your comments, identified by Docket ID No. EPA-R09-
OAR-2017-0177 at http://www.regulations.gov, or via email to Rory Mays
at [email protected]. For comments submitted at Regulations.gov, follow
the online instructions for submitting comments. Once submitted,
comments cannot be edited or removed 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 https://www.epa.gov/dockets/commenting-epa-dockets.

FOR FURTHER INFORMATION CONTACT: Rory Mays, Air Planning Office (AIR-
2), EPA Region IX,<PHONE_NUMBER>, [email protected].

SUPPLEMENTARY INFORMATION: Throughout this document, ``we'', ``us'' and
``our'' refer to the EPA.

Table of Contents

I. Background
    A. Interstate Transport
    B. California's Submission
II. Interstate Transport Evaluation
    A. The EPA's General Evaluation Approach
    B. Evaluation for the 2008 8-Hour Ozone NAAQS
    C. Evaluation for the 2006 PM2.5 and 2012
PM2.5 NAAQS
    D. Evaluation for the 2010 1-hour SO2 NAAQS
III. Proposed Action
IV. Statutory and Executive Order Reviews

I. Background

    Section 110(a)(1) of the CAA requires states to submit SIPs meeting
the applicable requirements of section 110(a)(2) within three years
after promulgation of a new or revised NAAQS or within such shorter
period as the EPA may prescribe. Section 110(a)(2) requires states to
address structural SIP elements such as requirements for monitoring,
basic program requirements, and legal authority that are designed to
provide for implementation, maintenance, and enforcement of the NAAQS.
The EPA refers to the SIP submissions required by these provisions as
``infrastructure SIP'' submissions. Section 110(a) imposes the
obligation upon states to make a SIP submission to the EPA for a new or
revised NAAQS, but the contents of individual state submissions may
vary depending upon the facts and circumstances. This proposed rule
pertains to the infrastructure SIP requirements for interstate
transport of air pollution.

A. Interstate Transport

    Section 110(a)(2)(D)(i) of the CAA requires SIPs to include
provisions prohibiting any source or other type of emissions activity
in one state from emitting any air pollutant in amounts that will
contribute significantly to nonattainment, or interfere with
maintenance, of the NAAQS, or interfere with measures required to
prevent significant deterioration of air quality or to protect
visibility in any other state. This proposed rule addresses the two
requirements under section 110(a)(2)(D)(i)(I), which we refer to as
prong 1 (significant contribution to nonattainment of the NAAQS in any
other state) and prong 2 (interference with maintenance of the NAAQS in
any other state).\1\ The EPA refers to SIP revisions addressing the
requirements of section 110(a)(2)(D)(i)(I) as ``good

neighbor SIPs'' or ``interstate transport SIPs.''
---------------------------------------------------------------------------

    \1\ The remaining interstate and international transport
requirements of CAA section 110(a)(2)(D) for the 2008 ozone, 2006
PM2.5, 2012 PM2.5, and 2010 SO2
NAAQS for California have been addressed in prior State submissions
and EPA rulemakings. 81 FR 18766 (April 1, 2016). Specifically, this
includes the section 110(a)(2)(D)(i)(II) requirements relating to
interference with measures required to be included in the applicable
implementation plan for any other state under part C to prevent
significant deterioration of air quality (prong 3) or to protect
visibility (prong 4), and the section 110(a)(2)(D)(ii) requirements
relating to interstate and international pollution abatement.
---------------------------------------------------------------------------

    Each of the following NAAQS revisions triggered the requirement for
states to submit infrastructure SIPs, including provisions to address
interstate transport prongs 1 and 2. On September 21, 2006, the EPA
revised the primary and secondary 24-hour NAAQS for PM2.5 to
35 micrograms per cubic meter ([micro]g/m\3\) and retained the primary
and secondary annual NAAQS for PM2.5 of 15.0 [micro]g/
m\3\.\2\ On March 12, 2008, the EPA revised the levels of the primary
and secondary 8-hour ozone standards to 0.075 parts per million
(ppm).\3\ On June 2, 2010, the EPA established a new primary 1-hour
SO2 standard of 75 ppb.\4\ Finally, on December 14, 2012,
the EPA revised the primary annual PM2.5 standard by
lowering the level to 12.0 [mu]g/m\3\ and retained the secondary annual
PM2.5 standard of 15.0 [micro]g/m\3\ and the primary and
secondary 24-hour PM2.5 standards of 35 [mu]g/m\3\.\5\
---------------------------------------------------------------------------

    \2\ 71 FR 61144 (October 17, 2006). Regarding the annual
PM2.5 standards, we note that the EPA previously approved
a California SIP submission for the 1997 PM2.5 NAAQS (and
the 1997 ozone NAAQS) for interstate transport prongs 1 and 2. 76 FR
34872 (June 15, 2011).
    \3\ 73 FR 16436 (March 27, 2008).
    \4\ 75 FR 35520 (June 22, 2010).
    \5\ 78 FR 3086 (January 15, 2013).
---------------------------------------------------------------------------

    The EPA has issued several guidance documents and informational
memos that inform the states' development and the EPA's evaluation of
interstate transport SIPs for section 110(a)(2)(D)(i)(I). These include
the following memos relating to the NAAQS at issue in this proposed
rule:
     Information on interstate transport SIP requirements for
the 2008 ozone NAAQS (``Ozone Transport Memo''),\6\
---------------------------------------------------------------------------

    \6\ Memorandum from Stephen D. Page, Director, OAQPS, EPA,
``Information on Interstate Transport ``Good Neighbor'' Provision
for the 2008 Ozone National Ambient Air Quality Standards (NAAQS)
under Clean Air Act (CAA) Section 110(a)(2)(D)(i)(I),'' January 22,
2015.
---------------------------------------------------------------------------

     Cross-State Air Pollution Rule (CSAPR) Update ozone
transport modeling (``CSAPR Update Modeling''),\7\
---------------------------------------------------------------------------

    \7\ The EPA updated its ozone transport modeling through the
CSAPR Update rulemaking. 81 FR 74504 (October 26, 2016). The
modeling results are found in the ``Ozone Transport Policy Analysis
Final Rule TSD,'' EPA, August 2016, and an update to the affiliated
final CSAPR Update ozone design value and contributions spreadsheet
that includes additional analysis by EPA Region IX (``CSAPR Update
Modeling Results and EPA Region IX Analysis'').
---------------------------------------------------------------------------

     Supplemental information on interstate transport SIP
requirements for the 2008 ozone NAAQS (``Supplemental Ozone Transport
Memo''),\8\
---------------------------------------------------------------------------

    \8\ Memorandum from Stephen D. Page, Director, OAQPS, EPA,
``Supplemental Information on the Interstate Transport State
Implementation Plan Submissions for the 2008 Ozone National Ambient
Air Quality Standards under Clean Air Act Section
110(a)(2)(D)(i)(I),'' October 27, 2017.
---------------------------------------------------------------------------

     Guidance on infrastructure SIP requirements for the 2006
PM2.5 NAAQS (``2006 PM2.5 NAAQS Transport
Guidance''),\9\ and
---------------------------------------------------------------------------

    \9\ Memorandum from William T. Harnett, Director, Air Quality
Policy Division, OAQPS, EPA, ``Guidance on SIP Elements Required
Under Sections 110(a)(1) and (2) for the 2006 24-Hour Fine
Particulate Matter National Ambient Air Quality Standards,''
September 25, 2009.
---------------------------------------------------------------------------

     Information on interstate transport SIP requirements for
the 2012 PM2.5 NAAQS (``2012 PM2.5 NAAQS
Transport Memo'').\10\
---------------------------------------------------------------------------

    \10\ Memorandum from Stephen D. Page, Director, OAQPS, EPA,
``Information on Interstate Transport `Good Neighbor' Provision for
the 2012 Fine Particulate Matter National Ambient Air Quality
Standards under Clean Air Act Section 110(a)(2)(D)(i)(I),'' March
17, 2016.
---------------------------------------------------------------------------

    For the 2006 PM2.5 and 2008 ozone NAAQS, the EPA
previously found that California failed to submit the required SIP
revisions addressing interstate transport prongs 1 and 2 by certain
dates.\11\ Those actions triggered the obligation for the EPA to
promulgate a federal implementation plan (FIP) for these requirements
unless the State submits and the EPA approves a SIP submission that
addresses the two prongs. As discussed further in this notice, the EPA
proposes that California's interstate transport SIP submission
adequately addresses these requirements for the 2006 PM2.5
and 2008 ozone NAAQS, as well as the 2012 PM2.5 and 2010
SO2 NAAQS, for which the EPA has not made a finding of
failure to submit.
---------------------------------------------------------------------------

    \11\ 79 FR 63536 (October 24, 2014) for the 2006
PM2.5 NAAQS and 80 FR 39961 (July 13, 2015) for the 2008
ozone NAAQS.
---------------------------------------------------------------------------

B. California's Submission

    The California Air Resources Board (CARB) submitted the
``California Infrastructure State Implementation Plan (SIP) Revision,
Clean Air Act Section 110(a)(2)(D)'' on January 19, 2016 (``California
Transport Plan'' or ``Plan'').\12\ We are proposing action on the
California Transport Plan, which addresses interstate transport for the
2008 ozone, 2006 PM2.5, 2012 PM2.5, and 2010
SO2 NAAQS. We find that this submission meets the procedural
requirements for public participation under CAA section 110(a)(2) and
40 CFR 51.102.
---------------------------------------------------------------------------

    \12\ Letter from Richard W. Corey, Executive Officer, CARB to
Jared Blumenfeld, Regional Administrator, Region 9, EPA, January 19,
2016.
---------------------------------------------------------------------------

    The California Transport Plan outlines the CAA interstate transport
requirements, describes the State's and, to some degree, the local air
districts' emission limits and other control measures, and presents its
methodology for analyzing ozone, PM2.5, and SO2
transport and conclusions for each. It includes appendices with CARB's
analysis for each of the NAAQS addressed in the SIP submission,
PM2.5 data and graphics from selected Interagency Monitoring
of Protected Visual Environments (IMPROVE) monitors \13\ near areas in
other western states with elevated levels of ambient PM2.5,
emissions data from the 70 facilities closest to each PM2.5
receptor, and a list of CARB control measures for mobile sources of air
pollution.
---------------------------------------------------------------------------

    \13\ IMPROVE monitors are located in national parks and
wilderness areas to monitor air pollutants that impair visibility.
---------------------------------------------------------------------------

II. Interstate Transport Evaluation

A. The EPA's General Evaluation Approach

    We review the state's submission to see how it evaluates the
transport of air pollution to other states for a given air pollutant,
the types of information the state used in its analysis, how that
analysis compares with prior EPA rulemaking, modeling, and guidance,
and the conclusions drawn by the state. Taking stock of the state's
submission, the EPA generally evaluates the interstate transport of a
given pollutant through a stepwise process. The following discussion
addresses the EPA's approach to evaluating interstate transport for
regional pollutants such as ozone and PM2.5. Our evaluation
approach for interstate transport of SO2 is described in
section II.D.1 of this proposed rule.
    Typically, for assessing interstate transport for regional
pollutants, such as PM2.5 or ozone, we first identify the
areas that may have problems attaining or maintaining attainment of the
NAAQS. We refer to regulatory monitors that are expected to exceed the
NAAQS under average conditions as ``nonattainment receptors'' (i.e.,
not expected to attain) and those that may have difficulty maintaining
the NAAQS as ``maintenance receptors.'' \14\ Such receptors may include
regulatory monitors operated by states, tribes, or local air
agencies.\15\
---------------------------------------------------------------------------

    \14\ Regulatory monitoring sites are those that meet certain
siting and data quality requirements such that they may be used as a
basis for regulatory decisions with respect to a given NAAQS.
    \15\ In California, there are two federally-recognized tribes
that operate regulatory monitors for ozone or PM2.5: The
Morongo Band of Mission Indians operates a regulatory ozone monitor
and the Pechanga Band of Luise[ntilde]o Indians operates regulatory
monitors for both ozone and PM2.5.
---------------------------------------------------------------------------

    In some cases, we have identified these receptors by modeling air
quality in a future year that is relevant to CAA attainment deadlines
for a given NAAQS. This type of modeling has been

based on air quality data, emissions inventories, existing and planned
air pollution control measures, and other information. For purposes of
this proposed rule, such modeling is available for western states \16\
for the 2008 ozone and 2012 PM2.5 NAAQS; in each case the
EPA modeled air quality in the 48 contiguous states of the continental
U.S.\17\ When such modeling is not available, the EPA has considered
available relevant information, including recent air quality data. An
interstate transport SIP can rely on modeling when an appropriate
technical analysis is available, but the EPA does not believe that
modeling is necessarily required if other available information is
sufficient to evaluate the presence or degree of interstate transport.
Further, the EPA believes it is appropriate to identify areas that
violate the NAAQS or have the potential to violate the NAAQS within a
geographic scope that reflects the potential dispersion of certain air
pollutants. In the context of this proposed rule, this concept applies
to the 2006 PM2.5 NAAQS, where we focused on air quality
data in 10 western states outside of California, and the 2010
SO2 NAAQS, where we reviewed air quality data in the
California's three neighboring states (i.e., Arizona, Nevada, and
Oregon).\18\ Identifying such receptors or areas helps to focus
analytical efforts by the states and the EPA on the areas where
transported air pollution is more likely to adversely affect air
quality.
---------------------------------------------------------------------------

    \16\ For purposes of this proposed rule, ``western states''
refers to the states of Arizona, California, Colorado, Idaho,
Montana, Nevada, New Mexico, Oregon, Utah, Washington, and Wyoming.
    \17\ The methodology for the EPA's transport modeling for the
2008 ozone and 2012 PM2.5 NAAQS is described in the CSAPR
Update Rule (81 FR 74504, October 26, 2016) and the EPA's 2012
PM2.5 NAAQS Transport Memo, respectively. For the 2008
ozone NAAQS, 2017 is the attainment year for Moderate ozone
nonattainment areas. For the 2012 PM2.5 NAAQS, 2021 is
the attainment year for Moderate PM2.5 nonattainment
areas. While the EPA's 2016 Transport Modeling projected 24-hour
PM2.5 concentrations for 2017 and 2025, such data can be
used to inform analyses of interstate transport in 2021. The
California Transport Plan (pp. 16-17) also discusses the EPA's
regulatory framework with respect to ozone transport.
    \18\ The transport of SO2 is more analogous to the
transport of lead rather than regional pollutants like ozone and
PM2.5 because its physical properties result in localized
pollutant impacts very near the emissions source. For this reason,
we have evaluated SO2 interstate transport for the three,
large states that border California, rather than a larger geographic
area. For further discussion of the physical properties of
SO2 transport, please see the EPA's proposal on
Connecticut's SO2 transport SIP. 82 FR 21351 at 21352 and
21354 (May 8, 2017).
---------------------------------------------------------------------------

    After identifying potential receptors, the EPA's second step for
regional pollutants such as PM2.5 or ozone is to assess how
much the upwind state of interest (i.e., California) may contribute to
air pollution at each of the identified receptors or areas in other
states. The EPA has conducted contribution modeling for the 2008 ozone
NAAQS to estimate the amount of the projected average ozone design
value at each receptor that will result from the emissions of each
state within the continental U.S., and we have considered this modeling
in this proposed rule. The EPA has typically compared that contribution
amount (e.g., from California to Colorado) against an air quality
threshold, selected based on the level and nature of the contribution
from other states, as discussed in section II.B.2 of this proposed
rule. We use this information to determine whether further analysis of
the emission sources in a state is warranted (i.e., step 3). When the
EPA assesses state-to-state contribution, if we conclude that the
upwind state contributes only insignificant amounts to all
nonattainment and maintenance receptors or areas in other states, the
EPA may approve a submission that concludes that the submitting state
does not significantly contribute to nonattainment, or interfere with
maintenance, of the NAAQS in any other state.
    Third, if warranted based on step 2, the EPA analyzes emission
sources in the upwind state, including emission levels, state and
federal measures, and how well such sources are controlled. We also
review whether the applicable control measures are included in the SIP,
consistent with CAA section 110(a)(2)(D)(i). For example, for ozone,
this analysis has generally focused on the emissions of nitrogen oxides
(NOX), given that prior assessments of ozone control
approaches concluded that a NOX control strategy would be
most effective for reducing regional scale ozone transport,\19\ and on
large stationary sources, such as electricity generating units (EGUs),
given their historic potential to produce large, cost-effective
emission reductions.\20\
---------------------------------------------------------------------------

    \19\ For discussion of the effectiveness of control strategies
for NOX and volatile organic compounds (VOCs), which are
precursors to ozone, to reduce ozone levels in regional versus
densely urbanized scales, respectively, please see the EPA's
proposal for the Cross-State Air Pollution Rule (CSAPR). 75 FR
45210, 45235-45236 (August 2, 2010).
    \20\ For background on the EPA's regulatory approach to
interstate transport of ozone, beginning with the 1998
NOX SIP Call and the 2005 Clean Air Interstate Rule,
please see the EPA's CSAPR proposal. 75 FR 45210 at 45230-45232
(August 2, 2010).
---------------------------------------------------------------------------

    If contribution modeling is not available, we conduct a weight of
evidence analysis. This analysis is based on a review of the state's
submission and other available information, including air quality
trends; topographical, geographical, and meteorological information;
local emissions in downwind states and emissions from the upwind state;
and existing and planned emission control measures in the state of
interest. In CSAPR and for the 2012 PM2.5 NAAQS Transport
Memo, the EPA did not calculate the portion of any downwind state's
predicted PM2.5 concentrations that would result from
emissions from individual western states, such as California.
Accordingly, the EPA considers prong 1 and 2 submissions for states
outside the geographic area analyzed to develop CSAPR and the 2012
PM2.5 NAAQS Transport Memo to be appropriately evaluated
using a weight of evidence analysis of the best available information,
such as the information that EPA has recommended in the 2006
PM2.5 NAAQS Transport Guidance and 2012 PM2.5
NAAQS Transport Memo. For this proposed rule, we conducted weight of
evidence analyses to determine whether the emissions from California
significantly contribute to nonattainment, or interfere with
maintenance, of the NAAQS at each of the identified receptors (for the
2012 PM2.5 NAAQS) or identified areas (for the 2006
PM2.5 NAAQS and 2010 SO2 NAAQS).\21\ For the 2012
annual PM2.5 NAAQS, we consider both annual and 24-hour
PM2.5 data because, in many cases, the annual average
PM2.5 levels in the western U.S. are driven by an abundance
of high 24-hour average PM2.5 levels in winter.
---------------------------------------------------------------------------

    \21\ The California Transport Plan also includes such weight of
evidence analyses, though not necessarily to the same set of
receptors or areas identified in the EPA's analyses.
---------------------------------------------------------------------------

    At this point of our analysis, if we conclude that the SIP contains
adequate provisions to prohibit sources from emitting air pollutants
that significantly contribute to nonattainment, or interfere with
maintenance, of a given NAAQS in any other state, the EPA may approve a
submission that concludes that the state has sufficient measures to
prohibit significant contribution to nonattainment, or interference
with maintenance, of the NAAQS in any other state.
    If the EPA concludes that that the SIP does not meet the CAA
requirements, then the EPA must disapprove the state's submission with
respect to that NAAQS, and the disapproval action triggers the
obligation for the EPA to promulgate a FIP to address that deficiency.
Following such a disapproval, the state has an opportunity to resolve
any underlying

deficiency in the SIP. If the state does not address the deficiency,
then the CAA requires the EPA to issue a FIP to adequately prohibit
such emissions. The EPA has promulgated FIPs via regional interstate
transport rules across much of the eastern U.S. for the 1997 ozone,
1997 PM2.5, and 2006 PM2.5 NAAQS (CSAPR) \22\ and
for the 2008 ozone NAAQS (CSAPR Update).\23\ To date, no such FIP has
been promulgated with respect to CAA transport prongs 1 and 2 in the
western U.S., and we are not proposing any such FIP in this proposed
rule.
---------------------------------------------------------------------------

    \22\ 76 FR 48208 (August 8, 2011).
    \23\ 81 FR 74504 (October 26, 2016).
---------------------------------------------------------------------------

B. Evaluation for the 2008 8-Hour Ozone NAAQS

1. State's Submission
    The California Transport Plan presents a weight of evidence
analysis to assess whether emissions within the State contribute
significantly to nonattainment or interfere with maintenance of the
2008 ozone NAAQS in any other state. This analysis includes a review of
the EPA's photochemical modeling data that were available at the time
CARB developed its Plan (i.e., in the Ozone Transport Memo),\24\ air
quality data, downwind receptor sites, and the science of interstate
transport of air pollution in the western U.S. It focuses on potential
contributions to receptors in the Denver, Colorado area (four
receptors) and in Phoenix, Arizona (one receptor) based on the air
pollution linkages identified in the EPA's modeling.\25\
---------------------------------------------------------------------------

    \24\ 80 FR 46271 (August 4, 2015). This notice of data
availability (NODA) for the EPA's updated ozone transport modeling
data included the projected 2017 ozone design values at each
regulatory ozone monitor in the 48 continental U.S. states and
Washington, DC and the modeled linkages between upwind and downwind
states. Based on input received in response to the NODA and through
the EPA's CSAPR Update rulemaking, which was completed after the
California Transport Plan submission of January 19, 2016, the EPA
further updated the ozone transport modeling data. 81 FR 74504
(October 26, 2016).
    \25\ California Transport Plan, pp. 15, 18-19.
---------------------------------------------------------------------------

    CARB states that the EPA's Ozone Transport Memo considered an
upwind state to be linked to a downwind state if the upwind state's
projected contribution was over one percent of the NAAQS (i.e., one
percent is a 0.75 ppb contribution to an 8-hour average ozone
concentration).\26\ CARB also highlights a statement in the EPA's Ozone
Transport Memo that ozone transport in western states should be
evaluated on a case-by-case basis.\27\ The California Transport Plan
contrasts ozone levels and emission sources in the eastern versus the
western U.S. For states subject to CSAPR in the East, the Plan asserts
that emissions from upwind states overwhelm downwind local emission
contributions (i.e., local contributions are smaller than transported
contributions by an average ratio of 1:2) and multiple upwind states
affect a given downwind receptor. The Plan states that ozone levels in
the West are primarily driven by local emissions (i.e., by an average
ratio of 8:1), with a much smaller portion being attributed to
interstate transport, and that western states have widespread complex
terrain and are relatively larger on average than eastern states. The
Plan describes this contrast in further detail by discussing modeling
uncertainties.
---------------------------------------------------------------------------

    \26\ Id., p. 18 and App. D, pp. D-3 to D-7.
    \27\ See Ozone Transport Memo, p. 4.
---------------------------------------------------------------------------

    While acknowledging the possibility of some limited transport of
ozone or its precursor pollutants, CARB believes that there are
significant uncertainties in photochemical modeling of ozone transport
in the western U.S.\28\ CARB summarizes certain comments it made in
response to the EPA's August 2015 notice of data availability (NODA)
regarding ozone transport modeling.\29\ Those comments discuss the
challenge of modeling interstate transport of ozone in the western U.S.
due to complex terrain, wildfire effects, and the limited monitoring
data available to validate the modeling. CARB states that complex
terrain can enhance vertical mixing of air, serve as a barrier to
transported air pollution, enhance accumulation of local emissions in
basins and valleys, and influence air flows up, down, and across
valleys.\30\ Regarding wildfires, the Plan states that the size and
number of wildfires in the western U.S. have significantly increased in
recent decades and that wildfires can significantly increase ozone
levels in adjacent and downwind areas. CARB asserts that the EPA's
treatment of wildfire emissions in the Ozone Transport Memo modeling
has the potential to overestimate ozone concentrations in 2017 and to
underestimate the benefit of controlling anthropogenic emission
sources.\31\ CARB states that further analysis would be required to
quantify California's contribution with confidence.\32\
---------------------------------------------------------------------------

    \28\ California Transport Plan, p. 15.
    \29\ Id., pp. 15-16. See also, comment letter from K. Magliano,
Chief, Air Quality Planning and Science Division, CARB to the docket
of the EPA's NODA. 80 FR 46271 (August 4, 2015).
    \30\ California Transport Plan, App. D, pp. D-1 to D-2.
    \31\ California Transport Plan, p. 24.
    \32\ Id.
---------------------------------------------------------------------------

    Aside from the asserted modeling uncertainties, the Plan provides
analyses of California's potential impacts and information regarding
the Denver area and Phoenix receptors. For the Denver area
nonattainment and maintenance receptors identified in the EPA's Ozone
Transport Memo, CARB found it extremely unlikely that California
emission sources would affect such receptors on high ozone days.\33\
CARB describes distance (more than 600 miles, or 1,000 kilometers (km),
from California to Denver), topography (Denver is bounded by mountains
to the west and south) and meteorology (local wind flow patterns driven
by terrain and heat differentials) that would favor local ozone
formation and includes trajectory analyses of ozone concentrations at
the applicable receptors.\34\ This includes a description of the
location and topography at each nonattainment monitor (Air Quality
System (AQS) monitor ID 08-059-0006, Rocky Flats North; and 08-035-
0004, Chatfield State Park) and maintenance monitor (08-059-0011,
National Renewable Energy Laboratory (NREL); and 08-005-0002, Highland
Reservoir). CARB notes that the Chatfield nonattainment receptor and
the NREL maintenance receptor are 300-800 feet higher than the
elevation of Denver, away from sources whose emissions might scavenge
ozone,\35\ and west-southwest of Denver--an area to which winds push
emissions on days when meteorology is conducive to ozone formation.\36\
---------------------------------------------------------------------------

    \33\ Id., pp. 23-24 and App. D, p. D-25.
    \34\ Id., App. D, pp. D-19 to D-31.
    \35\ Ozone scavenging refers to a process where a molecule such
as nitric oxide strips an oxygen atom from ozone, thereby reducing
the amount of ozone in the atmosphere. For example, ozone
concentrations typically fall at night in urban areas due to
scavenging of ozone by NOX and other compounds. 73 FR
16436, 16490 (March 27, 2008).
    \36\ Id., p. D-23.
---------------------------------------------------------------------------

    Regarding its trajectory analysis, CARB examined the potential for
ozone or ozone precursor pollutants to travel from California to
Colorado using the Hybrid Single Particle Lagrangian Integrated
Trajectory model.\37\ CARB input ozone data from June and July in 2011
and 2012 as the months with the most high-ozone days and identified
only 11 of 447 back trajectories where pollution in the mixed layer of
air in Colorado went back to the mixed layer in California. CARB then
conducted forward trajectories for these 11 cases and found only one
where pollution in California's mixed layer reached the mixed layer at
a Colorado receptor. CARB concluded that the complex physical
environment between California and Colorado limits the reproducibility
of modeled transport of

air pollution. The Plan also describes a vertical cross-section profile
from the back trajectories and states that the air at the surface (in
California and/or Colorado) was almost always decoupled from the air
higher in the atmosphere, thus limiting the effect of transported air
pollution.
---------------------------------------------------------------------------

    \37\ Id., pp. D-23 to D-25.
---------------------------------------------------------------------------

    With respect to wildfires, CARB found an overall downward trend in
ozone concentrations at the four Colorado receptors from 2003 to 2010
followed by increases in 2011-2013, which coincide with large increases
in the acreage of wildland burned per year in Colorado (e.g., about
75,000 acres burned/year in 2009-2010 and about 190,000-255,000 acres
burned/year in 2011-2013).\38\ CARB states that the EPA's Ozone
Transport Memo modeling estimated 0.32-0.74 ppb of ozone was due to
wildfire at the four Colorado receptors, but that this estimate was
attributed only to ozone formed from the interaction of NOX
and volatile organic compounds (VOCs) emitted by such wildfires, and
not additional interactions of NOX and VOCs from wildfires
with NOX and VOCs from anthropogenic sources. CARB asserts
that this would underestimate the effect of wildfires on ozone levels
in 2011-2013, which in turn meant that the EPA's modeling overestimated
the predicted ozone concentrations at the Denver area receptors in
2017.\39\ CARB states that this would affect both the weighted design
values (of 2009-2013) used to identify 2017 nonattainment receptors and
contributions thereto and the highest design value (e.g., 2011-2013)
used to identify 2017 maintenance receptors and contributions
thereto.\40\ CARB suggests that a case-by-case approach may be needed
to adjust the weighting of years for base-year design values.
---------------------------------------------------------------------------

    \38\ Id., pp. D-26 to D-30.
    \39\ Id., pp. D-30 to D-31.
    \40\ For the primary and secondary ozone NAAQS, the design value
at each site is the 3-year average annual fourth-highest daily
maximum 8-hour average ozone concentration. 40 CFR part 50 App. I,
section 3.
---------------------------------------------------------------------------

    CARB concludes that physical and chemical processes occurring over
the complex terrain and the long distance from California to these
receptors would significantly affect any air pollution traveling
between the two states.\41\ Based on its analysis, CARB concludes that
California does not significantly contribute to nonattainment, or
interfere with maintenance, of the 2008 ozone NAAQS at the Denver area
receptors.
---------------------------------------------------------------------------

    \41\ California Transport Plan, pp. D-31 to D-32.
---------------------------------------------------------------------------

    For the Phoenix, Arizona receptor, CARB states that, while the
relatively shorter distance makes transport a possibility from southern
California, high ozone days in Phoenix are predominantly driven by
local contributions. CARB describes topography (e.g., Phoenix is in a
large bowl), meteorology (e.g., monsoon rains in July and August reduce
ozone levels, and highest ozone levels are observed in June), and a low
correspondence between modeled and measured high ozone concentrations
to support its assertion that high ozone days are driven by local
contributions.\42\ CARB asserts that California does not interfere with
maintenance of the 2008 ozone NAAQS at this maintenance receptor and
that CARB's on-going control programs will ensure that California does
not interfere with Phoenix maintaining the 2008 ozone NAAQS.
---------------------------------------------------------------------------

    \42\ Id., pp. D-13 to D-19.
---------------------------------------------------------------------------

    In addition, the California Transport Plan states that California
has responded to each successive ozone NAAQS with increasingly
stringent control measures and that CARB and other agencies' aggressive
emission control programs will continue to benefit air quality in
California and other states.\43\ The Plan states that CARB and local
air districts implement comprehensive rules to address emissions from
all source sectors.\44\ These programs and rules include measures on
mobile sources, the State's largest emission source sector, local air
district measures on stationary and area sources, and CARB regulations
on consumer products. CARB states that the EPA's Ozone Transport Memo
modeling takes into account many of California's existing measures and
shows that California emission reductions from 2011 to 2017 are 445
tons per day (tpd) of NOX and 277 tpd of reactive organic
gases (ROG).\45\
---------------------------------------------------------------------------

    \43\ Id., pp. 15, 24-25.
    \44\ Id., pp. D-7 to D-9.
    \45\ CARB typically refers to reactive organic gases in its
ozone-related submissions since VOCs in general can include both
reactive and unreactive gases. However, since ROG and VOC
inventories pertain to common chemical species (e.g., benzene,
xylene, etc.) we refer to this set of gases as VOCs in this proposed
rule.
---------------------------------------------------------------------------

    CARB highlights how its mobile source measures have often served as
models for federal mobile source control elements and that California's
legacy programs continue to provide current and future emission
reductions from vehicles within California and elsewhere. Where
California and federal rules have been harmonized, CARB has implemented
rules to accelerate deployment of the cleanest available control
technologies for heavy-duty trucks, buses, and construction equipment
to achieve emission reductions more quickly. Appendix G of the
California Transport Plan presents a list of regulatory actions taken
since 1985 to reduce mobile source emissions. CARB also describes
efforts underway to transition to near-zero vehicle emissions
technologies and to review the state's goods movement (e.g., via the
State's Sustainable Freight Action Plan, issued in July 2016). With
respect to stationary and area emission sources, the California
Transport Plan includes a table of 29 measures adopted by local air
districts and approved into the California SIP by the EPA.\46\ CARB
claims that these measures were not taken into account in the EPA's
Ozone Transport Memo modeling.
---------------------------------------------------------------------------

    \46\ California Transport Plan App. D, Table D-2, pp. D-9 to D-
12.
---------------------------------------------------------------------------

    The Plan concludes that neither the EPA's modeling, given CARB's
concerns about wildfire and model performance, nor CARB's weight of
evidence analysis indicates that California significantly contributes
to nonattainment, or interferes with maintenance, of the 2008 ozone
NAAQS in any other state. Therefore, CARB concludes that California
meets the requirements of CAA section 110(a)(2)(D)(i)(I) for the 2008
ozone NAAQS.
2. Introduction to the EPA's Ozone Evaluation
    The EPA agrees with the conclusion that California meets the CAA
requirements for interstate transport prongs 1 and 2 for the 2008 ozone
NAAQS. However, our rationale differs from that presented in the
California Transport Plan, as discussed below. First, we address CARB's
assertions regarding ozone transport modeling uncertainties for
identifying nonattainment and maintenance receptors in 2017 and
linkages to California. We then discuss the EPA's CSAPR Update
Modeling,\47\ which both decreased the number of receptors to which
California is linked relative to the EPA's Ozone Transport Memo
modeling and adjusted the estimates of California's contribution to
each projected 2017 receptor. We also discuss the contrast that CARB
draws between ozone transport in the eastern versus western U.S. These
components are important to the first two steps of our evaluation: (1)
To identify potential

nonattainment and maintenance receptors, and (2) to estimate interstate
contributions to those receptors. Based on that analysis, we propose to
find that California is not linked to any receptor in Arizona and
linked only to maintenance receptors in the Denver area in Colorado.
---------------------------------------------------------------------------

    \47\ As noted previously, the EPA updated its ozone transport
modeling through the CSAPR Update rulemaking. 81 FR 74504 (October
26, 2016). The modeling results are found in the ``Ozone Transport
Policy Analysis Final Rule TSD,'' EPA, August 2016, and an update to
the affiliated final CSAPR Update ozone design value and
contributions spreadsheet that includes additional analysis by EPA
Region IX (``CSAPR Update Modeling Results and EPA Region 9
Analysis'').
---------------------------------------------------------------------------

    With respect to California's linkage to those maintenance receptors
in Denver, we then present a general assessment of the emission sources
in California, including mobile and stationary emission sources. We
propose to find that control measures in the California SIP for mobile
sources, large EGUs, and large non-EGU sources (e.g., cement plants and
oil refineries), adequately prohibit the emission of air pollution in
amounts that will interfere with maintenance of the 2008 ozone NAAQS at
the identified receptors in the Denver area.
    Given the role of regulatory monitoring data in the EPA's analysis
of interstate transport, the regulatory monitoring performed by the
Morongo Band of Mission Indians (Morongo) and the Pechanga Band of
Luise[ntilde]o Indians (Pechanga), as well as comments from Morongo and
Pechanga during the EPA's rulemaking on California's interstate
transport SIP for the 1997 ozone and 1997 PM2.5 NAAQS,\48\
we have also considered transport to Morongo and Pechanga reservations.
Based on our review of the ambient air quality data of Morongo and
Pechanga and the emission control regimes of California's South Coast
Air Quality Management District (AQMD) for stationary sources and of
CARB for mobile sources, as described in the EPA's memo to the
docket,\49\ the EPA proposes to find that California adequately
prohibits the emission of air pollutants in amounts that will
significantly contribute to nonattainment, or interfere with
maintenance, of the 2008 ozone NAAQS in the Morongo or Pechanga
reservations.
---------------------------------------------------------------------------

    \48\ 76 FR 34872 (June 15, 2011). In their comments, Morongo and
Pechanga called for an analysis of any potential ozone or
PM2.5 transport to their reservations and for
consultation with the EPA.
    \49\ Memorandum from Rory Mays, Air Planning Office, Air
Division, Region IX, EPA, ``Interstate Transport for the 2008 ozone,
2006 PM2.5, 2012 PM2.5, and 2010
SO2 NAAQS and the Morongo Band of Mission Indians and the
Pechanga Band of Luise[ntilde]o Indians,'' January 2018.
---------------------------------------------------------------------------

3. Evaluation of CARB's Modeling Concerns
    The California Transport Plan asserts that uncertainty in the EPA's
Ozone Transport Memo modeling derives from issues of complex terrain,
wildfires, and model performance, and presents trajectory analyses to
supplement these uncertainties. We consider each of these factors
because they are important to the adequacy of the EPA's modeling data
with respect to ozone transport in the western U.S.
    We agree with CARB that the terrain in the western U.S. is complex
and can enhance vertical mixing of air, serve as a barrier to
transported air pollution, enhance accumulation of local emissions in
basins and valleys, and influence air flows up, down, and across
valleys. It is also true that California is a long distance (about
1,000 km) from the receptors identified in Colorado. The EPA used the
CSAPR Update Modeling in a relative sense to project measured design
values to 2017 and to quantify contributions from statewide 2017
anthropogenic emissions of NOX and VOC on a broad regional
basis.\50\ As such, it was important to use a large regional scale
modeling domain to adequately capture multi-day regional transport of
ozone and precursor pollutants over long distances. The EPA selected
the Comprehensive Air Quality Model with Extensions to perform such
modeling given its utility in regional photochemical dispersion
modeling and in developing quantitative contributions for evaluation of
the magnitude of ozone transport from upwind states. We believe the
EPA's CSAPR Update Modeling adequately accounts for the complex terrain
and distance.
---------------------------------------------------------------------------

    \50\ ``Cross State Air Pollution Update Rule--Response to
Comments'' (CSAPR Update RTC), EPA, October 2016, p. 66.
---------------------------------------------------------------------------

    The EPA responded to CARB's comments regarding potential wildfire
influences on modeling in our response to comments document for the
CSAPR Update final rule (``CSAPR Update RTC'').\51\ We acknowledge that
wildfires could influence downwind pollutant concentrations and that it
is likely that wildfires would occur in 2017 and future years. However,
there is no way to accurately forecast the timing, location, and extent
of fires across a future three-year period that would be used to
calculate ozone design values. In the EPA's CSAPR Update Modeling, the
EPA held the meteorological data and the fire and biogenic emissions
constant at base year levels in the future year modeling, as those
emissions are highly[hyphen]correlated with the meteorological
conditions in the base year.
---------------------------------------------------------------------------

    \51\ CSAPR Update RTC, pp. 25 and 27.
---------------------------------------------------------------------------

    Regarding model performance, CARB states that there are limited
monitoring data available to validate the EPA's ozone transport
modeling. We discuss our ozone transport modeling platform in section
V.A of the CSAPR Update, including our model performance assessment
using measured ozone concentrations.\52\ We compared the 8-hour daily
maximum ozone concentrations during the May through September ``ozone
season'' to the corresponding measured concentrations, generally
following the approach described in the EPA's draft modeling guidance
for ozone attainment.\53\ We found that the predicted 8-hour daily
maximum ozone concentrations reflect the corresponding measured
concentrations in the modeling domain in terms of magnitude, temporal
fluctuations, and spatial differences. The ozone model performance
results were within the range found in other recent peer-reviewed and
regulatory applications. We note that any problem posed by imperfect
model performance on individual days is expected to be reduced when
using a relative approach (i.e., using base year data to project
relative changes in a future year ozone design value), as was the case
in the EPA's CSAPR Update Modeling. In brief, we disagree with CARB's
perspective with respect to model performance.
---------------------------------------------------------------------------

    \52\ 81 FR 74504, 74526-74527 (October 26, 2016).
    \53\ ``Draft Modeling Guidance for Demonstrating Attainment of
Air Quality Goals for Ozone, PM2.5, and Regional Haze,''
EPA, December 3, 2014.
---------------------------------------------------------------------------

    CARB states that the complex physical environment between
California and Colorado limits the reproducibility of modeled transport
of air pollution and that further analysis would be required to
quantify California's contribution with confidence. We agree that such
research could prove valuable, particularly with respect to
implementing the more stringent 2015 ozone NAAQS.\54\ However, the
prospect of future research does not itself undermine the technical
adequacy of the EPA's current modeling for the 2008 ozone NAAQS.
---------------------------------------------------------------------------

    \54\ The EPA recently issued a NODA with our preliminary
interstate transport data for the 2015 ozone NAAQS, which projects
that California will have several nonattainment receptors, and
California and Colorado will have several maintenance receptors, in
2023. 82 FR 1733 (January 6, 2017).
---------------------------------------------------------------------------

    Having considered the effects of complex terrain, wildfires, and
any model performance in the EPA's ozone transport modeling for ozone
levels throughout the continental U.S. (i.e., not just the Denver area
receptors), we assert the EPA's approach to forecasting interstate
transport for the 2008 ozone NAAQS to be a reasonable means for
identifying nonattainment and maintenance receptors and for estimating
the state contributions to

those receptors. Thus, we turn to summarizing changes between the EPA's
Ozone Transport Memo modeling and CSAPR Update Modeling results as they
pertain to California's contribution to nonattainment and maintenance
receptors in other states.
4. Identification of Receptors and Estimation of California
Contribution
    The EPA noted in the CSAPR Update that there may be specific
geographic factors in western states to consider in evaluating
interstate transport and, given the near-term 2017 implementation
timeframe, the EPA focused the CSAPR Update on eastern states.\55\
Consistent with our statements in the CSAPR Update and other transport
actions in western states,\56\ the EPA intends to address western
states on a case-by-case basis.
---------------------------------------------------------------------------

    \55\ 81 FR 74504, 74523 (October 26, 2016).
    \56\ See, e.g., the EPA's proposed rule on Arizona's interstate
transport for the 2008 ozone NAAQS. 81 FR 15200 (March 22, 2016).
---------------------------------------------------------------------------

    As described in the California Transport Plan, the EPA's Ozone
Transport Memo identified two nonattainment and two maintenance
receptors in the Denver area and one maintenance receptor in Phoenix.
Based on input received in response to our Ozone Transport Memo NODA
and the CSAPR Update proposal, the EPA updated the ozone transport
modeling to reflect the latest data and analysis (e.g., emission
reductions from additional NOX control measures). In each
modeling exercise, we used the same definition for nonattainment
receptors: Regulatory ozone monitors where 2017 ozone design values are
projected to exceed the 2008 ozone NAAQS based on the average design
value of three overlapping periods (2009-2011, 2010-2012, and 2011-
2013) and where the monitor indicated nonattainment at the time of the
analysis for the CSAPR Update. Similarly, we used the same CSAPR Update
definition for maintenance receptors: Regulatory ozone monitors where
2017 ozone design values do not exceed the NAAQS based on the projected
average design values, but exceed the 2008 ozone NAAQS based on the
projected maximum design value of any period within the three
overlapping periods. In addition, monitoring sites that are projected
to have average design values above the NAAQS but currently have
measured design values below the NAAQS are also considered maintenance
receptors.
    The EPA's CSAPR Update Modeling projects that for the western U.S.
in 2017 (outside of California), there are no nonattainment receptors
and only three maintenance receptors located in the Denver, Colorado
area. Notably, that modeling projects that Phoenix, Arizona will not
have any receptors.\57\ California emissions are projected to
contribute above one percent of the 2008 ozone NAAQS at each of the
three Denver area maintenance receptors, as shown in Table 1.
---------------------------------------------------------------------------

    \57\ The EPA's 2016 Ozone Transport Modeling projects that the
2017 maximum base case design value in Maricopa County, Arizona (AQS
ID 40-013-1004) will be 75.7 ppb (i.e., 0.0757 ppm), which is
attaining the 2008 ozone NAAQS, per the data handling convention for
computing 8-hour ozone averages (i.e., truncating digits to the
right of the third decimal place of values presented in ppm). 40 CFR
part 50, Appendix P, section 2.1.

                                                 Table 1--2017 Ozone Maintenance Receptors in Colorado Based on the EPA's CSAPR Update Modeling
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                Other
                                                                                2017 base                                            states % of                               Number of
                                                                                case      California    California  Contribution   2017 base     Colorado        All         states
                 AQS monitor ID                                 County                  maximum    contribution   % of 2008     by other        case     contribution   remaining   contributing
                                                                                design        (ppb)     ozone NAAQS  states (ppb)    maximum        (ppb)       sources     over 1% of
                                                                                value (ppb)                                  \a\         design                     (ppb)         NAAQS
                                                                                value
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
08-035-0004.....................................  Douglas...........................         77.6          1.18          1.6          7.29          9.4         26.10        41.90             3
08-059-0006.....................................  Jefferson.........................         78.2          1.96          2.6          7.16          9.2         21.16        47.17             2
08-059-0011.....................................  Jefferson.........................         78.0          0.79          1.1          7.29          9.3         29.32        38.13             4
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
\a\ Contribution by other States includes contribution from states and tribes in the continental U.S., including California, that are outside of Colorado.

    The modeling shows that other states also contribute above one
percent of the NAAQS to these maintenance receptors. The EPA found that
the average interstate contribution to ozone concentrations from all
states upwind of these receptors ranged from 9.2 to 9.4 percent of the
projected ozone design values.\58\ Thus, the collective contribution of
emissions from upwind states represent a considerable portion of the
ozone concentrations at the maintenance receptors in the Denver area.
---------------------------------------------------------------------------

    \58\ CSAPR Update Modeling Results and EPA Region 9 Analysis.
---------------------------------------------------------------------------

    The EPA has historically found that the one percent threshold is
appropriate for identifying interstate transport linkages for states
collectively contributing to downwind ozone nonattainment or
maintenance problems because that threshold captures a high percentage
of the total pollution transport affecting downwind receptors.\59\ The
EPA believes a contribution from an individual state equal to or above
one percent of the NAAQS could be considered significant where the
collective contribution of emissions from one or more upwind states is
responsible for a considerable portion of the downwind air quality
problem regardless of where the receptor is geographically located. In
this case, combinations of two, three, or four states contribute
greater than or equal to one percent of the 2008 ozone NAAQS at each of
these three maintenance receptors, as shown in Table 1.
---------------------------------------------------------------------------

    \59\ See, e.g., 75 FR 45210, 45237 (August 2, 2010) and 76 FR
48208, 48238 (August 8, 2011) (CSAPR proposed and final rules); and
80 FR 75706, 75714 (December 3, 2015) and 81 FR 74504, 74518-74519
(October 26, 2016) (CSAPR Update proposed and final rules). See
also, e.g., 81 FR 15200, 15202-15203 (March 22, 2016) (proposed rule
on Arizona transport SIP, including prongs 1 and 2 for the 2008
ozone NAAQS); 81 FR 71991, 71992 (October 19, 2016) (final rule on
Utah transport SIPs, including prong 2 for the 2008 ozone NAAQS);
and 82 FR 9142, 9143 (February 3, 2017) (final rule on Wyoming
transport SIPs, including prongs 1 and 2 for the 2008 ozone NAAQS).
---------------------------------------------------------------------------

    Regarding CARB's comparison of the average ratio of local to
transported emissions in the East (1:2) versus the average ratio in the
West (8:1), while we did not quantitatively evaluate the ratios
presented in the California Transport Plan, we generally agree that
there could be substantial differences in such average ratios. However,
the value of comparing average ratios is somewhat limited given that
states within a particular region could have a wide variation of
contributions to other states. For example, the EPA's CSAPR Update
Modeling indicates that, excluding Texas, states collectively
contribute 9.4 percent to 16.2 percent of the projected 2017 base case
maximum ozone design values at each of three maintenance receptors in
Denton County (Dallas-Fort Worth area) and Harris County

(Houston), Texas.\60\ For each Texas receptor, two or three states each
contribute over one percent of the NAAQS. In comparison, we find that
two to four states each contribute over one percent of the NAAQS to
each of the Colorado maintenance receptors, which is similar to the
Texas scenario.
---------------------------------------------------------------------------

    \60\ CSAPR Update Modeling Results and EPA Region IX Analysis.
---------------------------------------------------------------------------

    Given these data and comparisons, the EPA is proposing that the one
percent threshold is also appropriate as an air quality threshold to
determine whether California is ``linked'' to the three maintenance
receptors in the Denver area for the 2008 ozone NAAQS.
    The EPA is not necessarily determining that one percent of the
NAAQS is always an appropriate threshold for identifying interstate
transport linkages for all states in the West. For example, the EPA
recently evaluated the impact of emissions from Arizona on two
projected nonattainment receptors identified in California and
concluded that, even though Arizona's modeled contribution was greater
than one percent of the 2008 ozone NAAQS, Arizona did not significantly
contribute to nonattainment, or interfere with maintenance, at those
receptors.\61\ Accordingly, where the facts and circumstances support a
different conclusion, the EPA has not always applied the one percent
threshold to identify states that may significantly contribute to
nonattainment, or interfere with maintenance, of the 2008 ozone NAAQS
in other states.
---------------------------------------------------------------------------

    \61\ Final rule, 81 FR 31513 (May 19, 2016). See also proposed
rule, 81 FR 15200, 15203 (March 22, 2016). The EPA evaluated the
nature of the ozone nonattainment problem at the California
receptors and determined that, unlike the receptors identified in
the eastern U.S. and unlike the maintenance receptors in Colorado,
only one state (Arizona) contributed above the one percent threshold
to the California receptors and that the total contribution from all
states linked to the receptors (2.5 to 4.4%) was negligible.
Considering this information, along with emissions inventories and
emissions projections showing Arizona emissions decreasing over
time, the EPA determined that Arizona had satisfied the requirements
of CAA section 110(a)(2)(D)(i)(I) with respect to the 2008 ozone
NAAQS.
---------------------------------------------------------------------------

    Likewise, the EPA is not determining that because California
contributes above the one percent threshold, it is necessarily making a
significant contribution that warrants further reductions in emissions.
As noted above, the one percent threshold identifies a state as
``linked,'' prompting further inquiry into whether the contributions
are significant and whether there are cost-effective controls that can
be employed to reduce emissions (i.e., the third step in our
evaluation).
    The EPA also notes that recent modeling shows that by the 2023
ozone season the receptors identified in Denver are projected to be
``clean,'' i.e., both the average and maximum design values are
projected to be below the level of the 2008 ozone NAAQS.\62\
---------------------------------------------------------------------------

    \62\ Supplemental Ozone Transport Memo, Attachment A, pp. A-7 to
A-8.
---------------------------------------------------------------------------

5. Evaluation of California Control Measures
    Based on the 2011 National Emissions Inventory (NEI) and the EPA's
CSAPR Update Modeling, California's anthropogenic NOX
emissions in 2011 were 1,944 tpd and its VOC emissions were 2,274 tpd.
These emissions came from mobile sources (i.e., on-road motor vehicles,
such as passenger cars, trucks, buses, and nonroad vehicles, such as
construction equipment, locomotives, ships, and aircraft), stationary
sources (e.g., EGU, non-EGU point, and oil and gas point and non-point
sources), and area sources (e.g., residential wood combustion). Based
on the EPA's CSAPR Update Modeling, California's anthropogenic
NOX emissions in 2017 were projected to be 1,409 tpd (a
decrease of 535 tpd, or 28 percent, from 2011), and its VOC emissions
were projected to be 1,972 tpd (a decrease of 302 tpd, or 13 percent,
from 2011). Table 2 shows the percentage of California NOX
and VOC emissions that came from mobile, stationary, and area sources,
based on the 2011 NEI and the 2017 emission projections.\63\
---------------------------------------------------------------------------

    \63\ Summary of 2017 projected California NOX and VOC
emissions workbooks, EPA, included in the docket to this proposed
rule as ``California--
2017ek_cb6v2_v6_11g_state_sector_totals.xlsx.'' We note that the EPA
estimated that California's NOX and VOC emission
reductions from 2011 to 2017 would be larger than the 445 tpd of
NOX and 227 tpd of VOC emission reductions that the State
projected in the California Transport Plan.

                    Table 2--California Emissions From the 2011 NEI and 2017 Projected Emissions From the EPA's CSAPR Update Modeling
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                NOX                                            VOCs
                                                         -----------------------------------------------------------------------------------------------
                                                            Mobile (%)    Stationary (%)     Area (%)       Mobile (%)    Stationary (%)     Area (%)
--------------------------------------------------------------------------------------------------------------------------------------------------------
2011 NEI Emissions (% of annual emissions)..............            78.4            11.2            10.4            34.8             6.5            58.7
2017 Projected Emissions (% of annual emissions)........            69.8            15.1            15.1            25.7             7.4            67.0
--------------------------------------------------------------------------------------------------------------------------------------------------------

    Both NOX and VOCs are precursors to ozone but, as noted
above, given that assessments of ozone control approaches concluded
that a NOX control strategy would be most effective for
reducing regional scale ozone transport, and consistent with the CSAPR
Update and prior interstate transport rulemakings, we have focused our
control measure review on sources of NOX.
    CARB identified numerous State mobile source measures and examples
of local air district stationary measures that control NOX
and VOCs emissions and have been approved into the California SIP, and
CARB stated that these measures are part of how California addresses
the CAA interstate transport requirements for the 2008 ozone NAAQS.\64\
Below, we discuss our evaluation of California's mobile source
measures, for which CARB has unique authority under State law, and
stationary source measures, which are adopted and implemented by
California's 35 local air districts. For the latter, beyond the
measures described in the California Transport Plan, we have also
considered stationary source control measures for EGUs, consistent with
the controls analysis for CSAPR, and examples of stationary source
control measures for the largest non-EGU sources in the State.
---------------------------------------------------------------------------

    \64\ California Transport Plan, App. G (state measures) and App.
D, pp. D-7 to D-12 (discussion of California emission control
programs, including recent local measures).
---------------------------------------------------------------------------

    As noted above, the mobile source sector is the largest source of
NOX in California and accounts for approximately 70 percent
of the projected 2017 NOX emissions. As a general matter,
the CAA assigns mobile source regulation to the EPA through

title II of the Act and, in so doing, preempts various types of state
regulation of mobile sources.\65\ However, for certain types of mobile
source emission standards, the State of California may request a waiver
(for new motor vehicles and new motor vehicle engines) or authorization
(for new and in-use nonroad engines and vehicles) for standards
relating to the control of emissions and accompanying enforcement
procedures, under CAA sections 209(b) and 209(e)(2), respectively.
---------------------------------------------------------------------------

    \65\ For further background on CAA title II authorities,
including the waiver and authorization process, particularly as they
apply to approval of CARB mobile source measures into the California
SIP, please see the EPA's proposed and final rules approving
numerous such measures. 80 FR 69915 (November 12, 2015) and 81 FR
39424 (June 16, 2016).
---------------------------------------------------------------------------

    Pursuant to CAA section 209(b) and (e)(2), CARB has requested, and
the EPA has approved, numerous waivers and authorizations over the
years, allowing CARB to establish a comprehensive program to control
and reduce mobile source emissions within the state. Once the
underlying regulations establishing the mobile source emissions
standards are waived or authorized by the EPA, CARB submits the
regulations to the EPA as revisions to the California SIP. In recent
years, the EPA has approved many such mobile source regulations as part
of the California SIP, including regulations establishing standards and
other requirements relating to emissions from cars, light- and medium-
duty trucks, heavy-duty trucks, commercial harbor craft, mobile cargo
handling equipment, marine engines and boats, and off-highway
recreational vehicles.\66\ To support and enhance these emissions
standards, CARB has also established specific gasoline and diesel fuel
requirements, and the California Bureau of Automotive Repair has
established a vehicle emissions and inspection (i.e., ``smog check'')
program.\67\
---------------------------------------------------------------------------

    \66\ 81 FR 39424 (June 16, 2016) and 82 FR 1446 (March 21,
2017).
    \67\ 75 FR 26653 (May 12, 2010) (revisions to California on-road
reformulated gasoline and diesel fuel regulations), and 75 FR 38023
(July 1, 2010) (revisions to California motor vehicle inspection and
maintenance program).
---------------------------------------------------------------------------

    Originally, CARB's mobile source control program focused on new
engines and vehicles. The emissions reductions from increasingly
stringent emissions standards for new engines and vehicles occur over
time as new, cleaner vehicles replace old, more polluting models in a
foreseeable process referred to as ``fleet turnover.'' In more recent
years, CARB has recognized that emissions reductions from the mobile
source sector due to fleet turnover would not occur quickly enough to
meet attainment deadlines established under the CAA. As a result, CARB
has expanded its program to address the emissions from in-use vehicles
(referred to as the ``legacy'' fleet) by establishing, for example,
retrofit or replacement requirements for certain types of heavy-duty
trucks and certain fleets of nonroad equipment.\68\
---------------------------------------------------------------------------

    \68\ 77 FR 20308 (April 4, 2012) (EPA approval of in-use truck
and bus regulation) and 81 FR 39424 (June 16, 2016) (EPA approval of
in-use off-road diesel-fueled fleets regulation).
---------------------------------------------------------------------------

    With respect to stationary and area emission sources, the
California Transport Plan states that local air districts implement
comprehensive rules to address emissions from all sectors.\69\ The
California SIP has hundreds of prohibitory rules that limit the
emission of NOX and VOCs.\70\ Many of these rules were
developed by local air districts to reduce ozone concentrations in the
numerous areas that were designated nonattainment for the 1979 1-hour
ozone and 1997 8-hour ozone NAAQS, including Severe (i.e., Coachella
Valley, Sacramento Metro, and Western Mojave Desert for both NAAQS, and
Ventura County for the 1-hour ozone NAAQS) and Extreme (i.e., Los
Angeles-South Coast and San Joaquin Valley) nonattainment areas.\71\
Generally, the planning requirements associated with the numerous
California ozone nonattainment areas, coupled with the increased
control requirement stringency for areas classified Severe and above
(e.g., lower major source thresholds and increasing permit offset
ratios), have served to limit emissions of NOX and VOCs from
California that might affect other states.
---------------------------------------------------------------------------

    \69\ California Transport Plan, App. D, p. D-7.
    \70\ For VOCs, these include rules limiting emissions from the
largest area, mobile, and stationary source categories such as
consumer products, farming operations, architectural coatings/
solvents, off-road equipment, light-duty passenger vehicles,
recreational boats, petroleum marketing, and coatings/process
solvents.
    \71\ Based on 2010 U.S. Census data, the total population in the
nonattainment areas for the 1997 ozone NAAQS was 34.7 million
people, including 23.1 million people in areas classified severe or
extreme. See https://www3.epa.gov/airquality/urbanair/sipstatus/reports/ca_areabypoll.html#ozone-8hr_1997_.
---------------------------------------------------------------------------

    The California Transport Plan includes a table of 29 measures
recently adopted by local air districts and approved into the
California SIP by the EPA. These measures are representative of the
wide array of NOX and VOC control measures employed by the
local air districts. For example, Ventura County Air Pollution Control
District (APCD) adopted rules limiting NOX emissions from
boilers, water heaters, and process heaters, and Santa Barbara County
APCD and South Coast AQMD adopted rules limiting NOX
emissions from certain types of central furnaces and water heaters. San
Joaquin Valley APCD adopted a rule to limit VOC emissions from
composting operations, and Sacramento Metropolitan AQMD adopted a rule
to limit VOC emissions from automotive and related equipment coatings
and solvents.
    In addition to the numerous SIP-approved state and local
regulations cited in the California Transport Plan, we also considered
California's control measures for NOX emissions from EGUs,
consistent with our approach for evaluating control measures in the
CSAPR Update and other interstate transport rulemakings, and other
large stationary sources in the state. For EGUs producing greater than
25 megawatts of electricity, including non-fossil fuel EGUs, the state-
wide NOX emissions rate in California is projected to be
0.0097 pounds of NOX per million British thermal units (lb/
MMBtu) in 2018.\72\ Thus, California ranks as the 47th lowest out of
the 48 contiguous states and Washington, DC, for which the EPA
performed power sector modeling in the context of the CSAPR Update.
---------------------------------------------------------------------------

    \72\ Ranking of NOX emission rate by state and
related spreadsheets, EPA, included in the docket to this proposed
rule as ``5.15_OS_NOX_AQM_Base_Case RPE File CA analysis
(2018 data).xlsx.''
---------------------------------------------------------------------------

    Furthermore, considering facility-level emissions and operations,
2016 emissions monitoring data indicate that 242 of the 244 EGUs in
California that reported ozone season NOX emissions to EPA
emitted NOX at rates less than or equal to 0.061 lb/
MMBtu.\73\ Two EGUs, Greenleaf One unit 1 and Redondo Beach unit 7,
emitted at rates higher than 0.061 lb/MMBtu. Greenleaf One unit 1
emitted less than 11 tons of NOX in the 2016 ozone season
and is therefore unlikely to have significant cost-effective emission
reduction opportunities. Applied Energy Services (AES) plans to retire
its Redondo Beach units, including unit 7, no later than December 31,
2019, to comply with California regulations on the use of cooling water
in certain power plant operations.\74\ In aggregate, these

assessments indicate that California produces electricity very
efficiently in terms of NOX emissions and is therefore
unlikely to have significant, further NOX reductions
available from the EGU sector at reasonable cost.
---------------------------------------------------------------------------

    \73\ 2016 ozone season NOX emissions and heat rate
data for California EGUs, EPA Air Markets Program Data, included in
the docket to this rulemaking and entitled ``2016 AMPD Ozone Season
NOX Emissions Heat Rate from California EGUs.xlsx.''
    \74\ ``Once-Through Cooling Phase-Out,'' California Energy
Commission, last updated March 8, 2017, Table 3, p. 6. Available at
http://www.energy.ca.gov/renewables/tracking_progress/documents/once_through_cooling.pdf. AES plans to retire Redondo Beach unit 7
by December 31, 2019, and units 5, 6, and 8 by December 31, 2020.
---------------------------------------------------------------------------

    The largest collection of EGU facilities emitting over 100 tons per
year (tpy) of NOX, per the 2011 NEI, are found in the San
Joaquin Valley, Bay Area, and South Coast air districts.\75\ These
sources are subject to district rules limiting NOX emissions
that have been approved into the California SIP.\76\ At least two of
these facilities in the San Joaquin Valley APCD have shut down since
2011.\77\ Otherwise, the largest NOX-emitting EGU facility
in 2011 was the ACE Cogeneration coal-fired power plant in Trona
(Mojave Desert AQMD). It emitted 620 tpy of NOX and was the
only EGU facility in California that emitted more than 250 tpy of
NOX. However, as discussed in the ACE Cogeneration Company's
2014 petition to the California Energy Commission to decommission this
facility, the company had signed an agreement with Southern California
Edison (the regional utility) to terminate operation of the facility in
December 2014 and, in fact, ceased operation on October 2, 2014.\78\
---------------------------------------------------------------------------

    \75\ 2011 NEI California emission inventory spreadsheet of
stationary sources emitting over 100 tpy NOX (``2011 NEI
CA NOX Spreadsheet''), included in the docket to this
rulemaking and entitled ``AIR17025--2011 NEI NOX sources
by CA air district--RIX Analysis.xlsx.'' The total emissions from
such sources in 2011 were 686 tpd in San Joaquin Valley APCD (five
facilities in Kern County), 474 tpd in Bay Area AQMD (four
facilities in Contra Costa County), and 394 tpd in South Coast AQMD
(one facility in each of Los Angeles, Riverside, and San Bernardino
Counties).
    \76\ For San Joaquin Valley APCD, see, e.g., Rule 4301 (``Fuel
Burning Equipment,'' amended December 17, 1992), 64 FR 26876 (May
18, 1999); Rule 4352 (``Solid Fuel Fired Boilers,'' amended December
15, 2011), 77 FR 66548 (November 6, 2012); Rule 4702 (``Internal
Combustion Engines,'' amended November 14, 2013), 81 FR 24029 (April
25, 2016); and Rule 4703 (``Stationary Gas Turbines,'' amended
September 20, 2007) 74 FR 53888 (October 21, 2009). For Bay Area
AQMD, see e.g., Regulation 9, Rule 11 (``Nitrogen Oxides and Carbon
Monoxide from Electric Power Generating Steam Boilers,'' amended May
17, 2000), 67 FR 35435 (May 20, 2002). For South Coast AQMD, see
e.g., Regulation 20 series rules for the Regional Clean Air
Incentives Market (RECLAIM) program. RECLAIM information is
available at: http://www.aqmd.gov/home/programs/business/business-detail?title=reclaim.
    \77\ The Rio Bravo Jasmin and Rio Bravo Poso biomass plants in
Bakersfield have closed and the San Joaquin Valley APCD has issued
emission reduction credit certificates for doing so on January 19,
2016. See http://www.valleyair.org/notices/Docs/2016/01-19-16_(S-
1153637)/S-1153637.pdf and http://www.valleyair.org/notices/Docs/2016/01-19-16_(S-1154416)/S-1154416.pdf, respectively.
    \78\ ``ACE Decommissioning Plan,'' ACE Cogeneration Company,
November 25, 2014, p. 1-1.
---------------------------------------------------------------------------

    To investigate the potential for further NOX emission
reductions from EGUs, the EPA assessed the cost effectiveness of
reducing NOX emissions from fossil fuel-fired EGUs in each
of the 48 contiguous states by estimating the amount of NOX
that would be emitted at certain levels of NOX control
stringency, represented by uniform regional cost thresholds from $800
per ton of NOX removed up to $6,400 per ton.\79\ The CSAPR
Update finalized EGU emission budgets for 22 eastern states based on a
cost threshold of $1,400 per ton since that level of cost-effective
control would achieve sufficient reductions to partially address ozone
transport in the eastern U.S. The NOX emission level for
California is flat at 1,905 tons across the cost threshold scenarios
until the $5,000 per ton scenario, where the California ozone season
NOX emission level would be reduced to 1,810 tons. In other
words, additional NOX reductions from EGUs in California
would cost more than three times the amount that the EPA determined to
be cost-effective to partially address ozone transport obligations in
the eastern U.S. under the CSAPR Update.
---------------------------------------------------------------------------

    \79\ ``Ozone Transport Policy Analysis Final Rule TSD,'' U.S.
EPA, August 2016, Table C-1, p. 15.
---------------------------------------------------------------------------

    Non-EGU stationary sources emitted 6.7 times more NOX
(61,074 tpy) than EGUs (9,159 tpy) in California, per the 2011 NEI, and
largely fall under the regulatory authority of California's local air
districts. Of these non-EGU stationary sources, 19 sources emitted over
500 tpy of NOX, per the 2011 NEI.\80\ These sources (and the
associated air districts) include: Six Portland cement plants (Kern
County, Mojave Desert, and Bay Area),\81\ nine petroleum refineries
(Bay Area and South Coast),\82\ and several other source types,
including a mineral processing plant (Mojave Desert), a natural gas
compressor station (Mojave Desert), a glass plant (San Joaquin
Valley),\83\ and a calcined pet coke plant (Bay Area).\84\ These 19
sources represent 67 percent of the NOX emissions from
California stationary sources that emitted over 100 tpy in 2011 and
represent 5.2 percent of the total 2011 NOX inventory for
California. Overall, these sources are subject to rules that limit
NOX emissions and have been approved into the California
SIP, as cited in the various footnotes of this paragraph. In light of
the overall control of such sources, for the small number of large non-
EGU sources that are either subject to NOX control measures
that have not been submitted for approval into the California SIP, or
fall outside the geographic jurisdiction of the applicable district
rules, our analysis finds that further emission controls would be
unlikely to reduce any potential impact on downwind states' air quality
because such sources comprise no more than 0.8 percent of the total
NOX emitted in California in 2011.\85\
---------------------------------------------------------------------------

    \80\ 2011 NEI CA NOX Spreadsheet. Other sources in
California emitting over 500 tpy of NOX include the Los
Angeles, San Francisco, San Diego, and other airports and the U.S.
Army National Training Center (Fort Irwin) and U.S. Marine Corps
Twentynine Palms military bases, whose NOX emissions from
aircraft are outside the regulatory authority of the State of
California. Separately, we do not count two Southern California
Edison substations in Antelope Valley AQMD among the sources listed
as emitting more than 500 tpy NOX., as we believe their
NOX emissions were recorded in error. They subsequently
do not appear in the 2014 NEI California emission inventory
spreadsheet of stationary sources emitting over 100 tpy
NOX (``2014 NEI CA NOX Spreadsheet''), which
is included in the docket to this rulemaking and entitled
``AIR17025--2014 NEI NOX sources by CA air district--RIX
Analysis.xlsx.''
    \81\ Kern County APCD Rule 425.3 (``Portland Cement Kilns
(Oxides of Nitrogen),'' amended October 13, 1994), 64 FR 38832 (July
20, 1999); Mojave Desert AQMD Rule 1161 (``Portland Cement Kilns,''
amended March 25, 2002), 68 FR 9015 (February 27, 2003); and Bay
Area AQMD Regulation 9, Rule 13 (``Nitrogen Oxides, Particulate
Matter, and Toxic Air Contaminants from Portland Cement
Manufacturing,'' amended October 19, 2016). The latter has not been
submitted by the Bay Area AQMD and CARB as a revision to the
California SIP.
    \82\ Bay Area AQMD Regulation 9, Rule 10 (``Nitrogen oxides and
Carbon Monoxide from Boilers, Steam Generators and Process Heaters
in Petroleum Refineries,'' amended July 17, 2002), 73 FR 17897
(April 2, 2008); and South Coast AQMD RECLAIM program, whose rules
have been approved into the California SIP, as noted above.
    \83\ San Joaquin Valley Rule 4354 (``Glass Melting Furnaces,''
amended May 19, 2011). Notably, the parent company of the Pilkington
North America, Inc. glass plant in Lathrop announced that the plant
was to be closed by January 1, 2014. http://www.recordnet.com/article/20131113/A_BIZ/311130312. Consistent with closure, it does
not appear in the 2014 NEI CA NOX Spreadsheet.
    \84\ Bay Area AQMD Regulation 9, Rule 10 (``Nitrogen Oxides and
Carbon Monoxide from Boilers, Steam Generators, and Process Heaters
in Petroleum Refineries'', amended July 17, 2002), 73 FR 17897
(April 2, 2008). This rule applies to some (e.g., process heaters),
but not all (e.g., the plant's coker unit), of the applicable
calcined petroleum coke plant's equipment.
    \85\ 2011 NEI CA NOX Spreadsheet.
---------------------------------------------------------------------------

    On the strength of CARB and the local air districts' emission
control programs, especially for mobile and stationary sources of
NOX, we propose that the California SIP, as explained in the
California Transport Plan and our evaluation above, adequately
prohibits the emission of air pollutants in amounts that will
significantly contribute to nonattainment, or interfere with
maintenance, of the 2008 ozone NAAQS in any other state. We agree with
CARB that California meets the requirements of CAA section

110(a)(2)(D)(i)(I) for the 2008 ozone NAAQS, but we differ as to the
rationale for that conclusion. California's analysis relies primarily
on its conclusion that the ozone transport linkages are uncertain and
therefore no significant contribution of interference with maintenance
has been demonstrated. The EPA's evaluation finds that the transport
linkages are adequately quantified (and uncertainties sufficiently
addressed) and that California's emission control programs adequately
address the transport requirements.

C. Evaluation for the 2006 PM2.5 and 2012 PM2.5 NAAQS

1. State's Submission
    The California Transport Plan presents a weight of evidence
analysis to assess whether the state contributes significantly to
nonattainment or interferes with maintenance of the 2006 24-hour
PM2.5 and 2012 annual PM2.5 NAAQS in any other
state. This analysis includes a review of air quality data for
California and other states, including daily 24-hour PM2.5
concentrations at potential downwind receptors and PM2.5
design value concentrations at IMPROVE monitoring sites; local
emissions near, distance to, and changes in population and vehicle
miles traveled (VMT) in areas near downwind receptors; California
emissions and rules and regulations to reduce such emissions; and other
information available from the EPA and other states' technical support
documents (TSDs) for various CAA requirements.\86\
---------------------------------------------------------------------------

    \86\ California Transport Plan, pp. 11-12.
---------------------------------------------------------------------------

    Regarding air quality data, CARB reviewed PM2.5 design
values in western states from the EPA's air trends website for three
overlapping periods between 2010-2014.\87\ For the purpose of
identifying potential receptors, CARB defined nonattainment receptors
as monitors violating the 2006 24-hour PM2.5 NAAQS (35
[micro]g/m\3\) or the 2012 annual PM2.5 NAAQS (12.0
[micro]g/m\3\) in 2012-2014 and maintenance receptors as those that
attained the NAAQS in that period, but violated the NAAQS in either of
the two preceding periods (2010-2012 or 2011-2013).
---------------------------------------------------------------------------

    \87\ Id., p. 10. The EPA's air trends website is available at:
https://www.epa.gov/air-trends.
---------------------------------------------------------------------------

    For the 24-hour PM2.5 standard, CARB identified 17
nonattainment receptors, with design values ranging from 36-61
[micro]g/m\3\, across the following five states listed by the
receptors' counties: Arizona (Pinal), Idaho (Lemhi and Shoshone),
Montana (Ravalli and Silver Bow), Oregon (Crook, Jackson, Lake, and
Lane), and Utah (Box Elder, Cache, Davis, Salt Lake, and Utah).\88\
CARB also identified four maintenance receptors, with design values
ranging from 36-39 [micro]g/m\3\ in either the 2010-2012 or 2011-2013
periods, across three states listed by the receptors' counties: Montana
(Lewis and Clark, and Missoula), Oregon (Klamath), and Utah (Weber).
---------------------------------------------------------------------------

    \88\ Id., p. 11, Tables III.1 and III.2.
---------------------------------------------------------------------------

    For the annual PM2.5 standard, CARB identified two
nonattainment receptors (i.e., having design values over 12.0 [micro]g/
m\3\), with design values of 12.1 and 13.1 [micro]g/m\3\, respectively,
and no maintenance receptors, in just one state listed by the
receptors' counties: Idaho (Lemhi and Shoshone).
    The California Transport Plan discusses California emissions from
mobile, stationary, and area sources and applicable regulatory
programs. CARB highlights the authority granted by Congress in the 1970
CAA for California to adopt mobile source emission control standards in
certain situations. Within the California Health and Safety Code, CARB
highlights the authority granted to CARB to adopt and implement
controls on mobile sources and their fuels, as well as consumer
products, and to the state's 35 local air districts to adopt and
implement stationary and area source controls.\89\ For mobile sources,
CARB states that it has adopted and implemented: ``fleet rules'' for
heavy-duty trucks, buses, and construction equipment; light-duty
vehicle and fuel regulations, such as the LEV III program and the 2012
Advanced Clean Car regulation; and inspection and maintenance programs
for light duty (i.e., smog check) and heavy-duty vehicles; among other
measures. For stationary and area sources, CARB states that local air
district rules, in combination, are among the most stringent in the
U.S. and cover a wide range of sources such as refineries,
manufacturing facilities, cement plants, refinishing operations,
electricity generation and biomass facilities, boilers, and generators.
---------------------------------------------------------------------------

    \89\ Id., pp. 5-6. As noted in section II.B.1 of this proposed
rule, Appendix G of the California Transport Plan presents a list of
CARB regulatory actions taken since 1985 to reduction mobile source
emissions.
---------------------------------------------------------------------------

    The California Transport Plan includes a sample list of State and
local air district rules that have been approved into the California
SIP and a graph of how California state-wide emissions of
PM2.5, and PM2.5 precursor pollutants, such as
NOX, VOC, and sulfur oxides (SOX), have decreased
significantly from 2001 (~7,000 tpd) to 2011 (~4,300 tpd) and are
expected to continue to decrease to 2021 (projected to be ~3,100
tpd).\90\ For example, the list includes CARB regulations for heavy-
duty trucks and buses and light- and medium-duty vehicles, and air
district regulations for open burning, agricultural burning, and
fugitive dust as example of regulations that limit the emission of
particulate matter. CARB states that these state and local programs
have reduced and will continue to reduce the potential for California
emissions to contribute to violations, or interfere with maintenance,
of the federal standards.
---------------------------------------------------------------------------

    \90\ Id., pp. 7-9, Table II.1 and Figure II.1. CARB's analysis
of California SO2 emissions in based on SOX
because CARB estimates that SO2 comprises 97% of the
state-wide SOX inventory. California Transport Plan, App.
C, p. C-10.
---------------------------------------------------------------------------

    We have further summarized the California Transport Plan in terms
of California's emissions and the State and local regulatory programs
in sections II.B and II.D of this proposed rule. These sections
describe CARB's statements with respect to NOX and VOC
emissions (for the 2008 ozone NAAQS) and SOX emissions (for
the 2010 SO2 NAAQS) and are relevant, as precursors to
PM2.5, to interstate transport for the 2006 PM2.5
and 2012 PM2.5 NAAQS. For example, CARB states that
NOX and VOC emissions have been reduced by 445 tpd and 277
tpd, respectively, from 2011 to 2017 due to California's regulatory
programs.\91\ Similarly, from 2000 to 2015, CARB estimates that CARB
and the air districts achieved the following SOX emission
reductions: Stationary sources (59 percent), mobile sources (88
percent), and area sources (33 percent).\92\
---------------------------------------------------------------------------

    \91\ Id., App. D, p. D-8.
    \92\ Id., App. C, p. C-3.
---------------------------------------------------------------------------

    Regarding assessment of the causes of the PM2.5
concentrations at each receptor, CARB presents its analysis for each
county or PM2.5 nonattainment area (e.g., the Salt Lake City
nonattainment area for the 2006 PM2.5 NAAQS, which includes
the receptors in Box Elder, Davis, and Salt Lake Counties). CARB's
receptor analyses focus on local emission sources, the distance between
California and each receptor, long-term PM2.5 trends and
daily PM2.5 data (as opposed to design values), population,
and VMT. These analyses appear in Appendix A of the California
Transport Plan for the 2006 24-hour PM2.5 NAAQS and in
Appendix B for the 2012 annual PM2.5 NAAQS. CARB includes
additional analyses of air quality data at IMPROVE sites that are
located between California and the receptor counties in Appendix E and
uses these data as an indicator of whether elevated PM2.5
levels are observed regionally. We discuss the

State's analysis of each receptor area in greater detail as part of our
evaluation for each PM2.5 NAAQS, below.
    For the 2006 24-hour PM2.5 NAAQS, CARB relies in part on
technical documents from applicable states and the EPA (e.g., TSDs for
the 2006 PM2.5 NAAQS nonattainment area designations) in
concluding that most exceedances at each nonattainment or maintenance
receptor are due to emissions from local sources, especially during
winter-time inversions.\93\ CARB further concludes that California
emissions from stationary sources are subject to stringent limits for
PM2.5 and its precursors, such as those for NOX
and SOX, and that California has a long history of reducing
emissions through motor vehicle and fuel standards. CARB also finds
that monitors in western states generally have valid design values well
below 35 [micro]g/m\3\, except for the 17 receptors identified in
CARB's analysis. Based on these analyses, CARB states that California
does not contribute to, or interfere with maintenance of, the 2006
PM2.5 NAAQS in neighboring or nearby states.
---------------------------------------------------------------------------

    \93\ Id., p. 22.
---------------------------------------------------------------------------

    For the 2012 annual PM2.5 NAAQS, CARB draws similar
conclusions as those for its 24-hour PM2.5 analyses: That
most of the high, annual PM2.5 concentrations are due to
local emissions, especially during winter-time inversions; that
California's stationary and mobile sources are well regulated; and that
monitors in western states generally have valid design values well
below 12.0 [micro]g/m\3\, except for the two receptors identified in
CARB's analysis.\94\ CARB concludes that California does not contribute
to, or interfere with maintenance of, the 2012 PM2.5 NAAQS
in neighboring or nearby states.
---------------------------------------------------------------------------

    \94\ Id., p. 22-23.
---------------------------------------------------------------------------

2. Introduction to the EPA's PM2.5 Evaluation
    The EPA agrees with CARB's conclusions that California meets the
CAA requirements for interstate transport prongs 1 and 2 for the 2006
PM2.5 and 2012 PM2.5 NAAQS, as discussed below.
First, we discuss our evaluation of CARB's identification of
nonattainment and maintenance receptors in western states based on data
presented in the California Transport Plan as well as the EPA's
analysis of 2009-2013 24-hour and annual PM2.5 design
values. Based on this analysis, we present modified lists of such
receptors (i.e., step one) that largely follow the lists of receptors
in the California Transport Plan, as presented in Table 3 (for the 2006
PM2.5 NAAQS) and Table 4 (for the 2012 PM2.5
NAAQS) of this proposed rule. We include data on the most recent, valid
design values (e.g., 2014-2016) for each receptor. We then discuss
California emissions of PM2.5 and its precursors,
California's regulations to limit such emissions, and the emission
trends resulting from such regulations.
    Building on the identification of potential nonattainment and
maintenance receptors and our discussion of California emissions, we
present our own weight of evidence analysis for addressing the CAA
requirements. This analysis affirms CARB's weight of evidence analysis
for the 2006 24-hour PM2.5 and 2012 annual PM2.5
NAAQS. Like the analytical approach used in the California Transport
Plan, for each potential receptor area we summarize our analyses of air
quality data at the applicable receptors, daily 24-hour
PM2.5 concentrations at the receptors, PM2.5
design value concentrations at IMPROVE monitoring sites,\95\ local
emissions and other local factors, and California's emission control
programs. We prepared a TSD containing our more detailed analysis of
interstate transport for the 2006 24-hour PM2.5 NAAQS
(``EPA's PM2.5 Transport TSD''), which is also relevant for
our evaluation of the 2012 annual PM2.5 NAAQS, and it is
included in the docket of this proposed rule.\96\
---------------------------------------------------------------------------

    \95\ Air quality data from IMPROVE monitoring sites may provide
an indication of rural background PM2.5 concentrations.
Low PM2.5 concentrations at IMPROVE sites that coincide
temporally with high PM2.5 concentrations at nearby
PM2.5 receptors may indicate a relatively localized
pollution impact, whereas high PM2.5 concentrations at
IMPROVE sites may indicate a more regional pollution impact.
    \96\ ``EPA Evaluation of the California Interstate Transport
Plan (2006 PM2.5 NAAQS), Technical Support Document,''
EPA, Region 9, January 2018.
---------------------------------------------------------------------------

    Given the role of regulatory monitoring data in the EPA's analysis
of interstate transport, the PM2.5 regulatory monitoring
performed by Pechanga, as well as comments from the Morongo and
Pechanga during the EPA's rulemaking on California's interstate
transport SIP for the 1997 ozone and 1997 PM2.5 NAAQS,\97\
we have also considered transport to the Morongo and Pechanga
reservations. Based on our review of such ambient air quality data, as
described in the EPA's memo to the docket referenced here,\98\ the EPA
proposes to find that the 24-hour and annual PM2.5 design
value concentrations at the Pechanga monitor and at monitors nearest to
the Morongo reservation fall below the levels of the 2006 24-hour
PM2.5 NAAQS and the 2012 annual PM2.5 NAAQS, and
thus do not warrant further analysis with respect to interstate
transport under CAA section 110(a)(2)(D)(i)(I) for any potential
PM2.5 air quality impacts in the Morongo or Pechanga
reservations.
---------------------------------------------------------------------------

    \97\ 76 FR 34872 (June 15, 2011). In their comments, Morongo and
Pechanga called for an analysis of any potential ozone or
PM2.5 transport to their reservations and for
consultation with the EPA.
    \98\ Memorandum from Rory Mays, Air Planning Office, Air
Division, Region XI, EPA, ``Interstate Transport for the 2008 ozone,
2006 PM2.5, 2012 PM2.5, and 2010
SO2 NAAQS and the Morongo Band of Mission Indians and the
Pechanga Band of Luise[ntilde]o Indians,'' January 2018.
---------------------------------------------------------------------------

3. Identification of Receptors
    The EPA's 2012 PM2.5 NAAQS Transport Memo was released
on March 17, 2016, and presented air quality modeling that identified
potential nonattainment and maintenance receptors.\99\ The EPA's
analysis used ambient PM2.5 data from 2009-2013, emissions
inventory data from the 2011 NEI, photochemical modeling for a 2011
base year and 2017 and 2025 future years, and other information to
project annual PM2.5 design values for 2017 and 2025. As
identified in the 2012 PM2.5 NAAQS Transport Memo, it may be
appropriate to use this information to help evaluate projected air
quality in 2021, which is the attainment deadline for 2012
PM2.5 NAAQS nonattainment areas classified as Moderate.
Because modeling results are only available for 2017 and 2025, one way
to assess potential receptors for 2021 is to assume that receptors
projected to have average and/or maximum design values above the NAAQS
in both 2017 and 2025 are also likely to be either nonattainment or
maintenance receptors in 2021. Similarly, it may be reasonable to
assume that receptors that are projected to attain the NAAQS in both
2017 and 2025 are not likely to have nonattainment or maintenance
problems in 2021.
---------------------------------------------------------------------------

    \99\ 2012 PM2.5 NAAQS Transport Memo, Table 1, p. 5.
---------------------------------------------------------------------------

    Where available, we rely on this kind of modeling for interstate
transport because it accounts for the effect of emission reductions
from planned federal, state, and local measures, as well as input from
state, local, industry, and community entities, to project where
violations, or potential violations, of the NAAQS will occur. By
aligning the overlapping design value periods (2009-2013) with the 2011
NEI, we can establish an improved understanding of the relationship
between emissions of PM2.5 and its precursors to ambient
PM2.5 concentrations. We have also considered the recent
2014-2016 design values at the potential nonattainment

and maintenance receptors identified in the EPA's 2012 PM2.5
NAAQS Transport Memo.
    We note that CARB's adoption of the California Transport Plan on
December 17, 2015, preceded the release of the EPA's 2012
PM2.5 NAAQS Transport Memo. CARB analyzed the overlapping
design value periods of 2010-2014, albeit without projecting those
values forward. Given the utility of the EPA's modeling for the reasons
described above, we have used the list of receptors from the EPA's 2012
PM2.5 NAAQS Transport Memo as the primary basis for our
evaluation, while also considering the differences in CARB's list of
receptors. In addition, we present the 2014-2016 design value data at
each identified receptor to indicate current air quality. The EPA's
list of receptors for the 2012 PM2.5 NAAQS appears in Table
4.
    For the 2006 PM2.5 NAAQS we have derived a list of
receptors using 2009-2013 design values as the primary basis for our
evaluation, while considering the differences in CARB's list of
receptors, as well as the most recent, valid design values (2014-2016,
where available). We selected this approach to provide a common base of
ambient air quality and emissions information for PM2.5 for
both the 24-hour and annual standards. Because neither the EPA nor CARB
modeled future 24-hour PM2.5 design values, we use the same
conceptual definition for 24-hour PM2.5 receptors from the
California Transport Plan--nonattainment receptors are those that
violate the 2006 24-hour PM2.5 NAAQS in the last of three
overlapping design value periods (2011-2013); and maintenance receptors
are those that attain the 2006 24-hour PM2.5 NAAQS in the
latest period, but violate the standard in either of the preceding two
design value periods (2009-2011 or 2010-2012). As with the annual
standard, we also present the 2014-2016 24-hour PM2.5 design
values at each identified receptor. The EPA's list of receptors for the
2006 PM2.5 NAAQS appears in Table 3.\100\
---------------------------------------------------------------------------

    \100\ Consistent with prior western interstate transport
actions, we have excluded from this list the receptors in Ravalli,
Montana (AQS ID 30-081-0007), Missoula, Montana (AQS ID 30-063-
0024), and Jackson, Oregon (AQS ID 41-029-0133) with design values
that may have been affected by wildfires. See, e.g., 80 FR 9423
(February 23, 2015), ``Technical Support Document--Idaho [SIP] and
Interstate Transport Requirements for the 2006 24-hour
[PM2.5 NAAQS],'' EPA, Region X, January 22, 2015, p. 12.

                                             Table 3--EPA List of Potential Nonattainment and Maintenance Receptors for the 2006 24-Hour PM2.5 NAAQS
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                Most recent valid
                                                             Nonattainment area for                                                                                design value
               State                         County           2006 PM2.5 NAAQS \a\       AQS ID      CARB receptor type (2010-2014 data)   EPA receptor type (2009-2013 data)   ([micro]g/m\3\)
                                                                                (2014-2016,
                                                                                except as noted)
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Arizona............................  Pinal.................  West Central Pinal....     04-021-3013  Nonattainment......................  (Nonattainment) \b\................                 30
Idaho..............................  Ada...................  ......................     16-001-0010  Not discussed......................  Nonattainment......................     19 (2008-2010)
Idaho..............................  Franklin..............  Logan.................     16-041-0001  Discussed with Cache County, Utah..  Nonattainment......................     46 (2008-2010)
Idaho..............................  Lemhi.................  ......................     16-059-0004  Nonattainment......................  Nonattainment......................                 41
Idaho..............................  Shoshone..............  West Silver Valley         16-079-0017  Nonattainment......................  Nonattainment......................                 39
                                                              (2012 PM2.5 NAAQS).
Montana............................  Silver Bow............  ......................     30-093-0005  Nonattainment......................  Nonattainment......................                 33
Oregon.............................  Crook.................  ......................     41-013-0100  Nonattainment......................  Nonattainment......................                 38
Oregon.............................  Lake..................  ......................     41-037-0001  Nonattainment......................  Nonattainment......................     56 (2013-2015)
Oregon.............................  Lane..................  Oakridge..............     41-039-2013  Nonattainment......................  Nonattainment......................                 31
Oregon.............................  Klamath...............  Klamath Falls.........     41-035-0004  Maintenance........................  Nonattainment......................                 27
Utah...............................  Box Elder.............  Salt Lake City........     49-003-0003  Nonattainment......................  Nonattainment......................                 31
Utah...............................  Cache.................  Logan.................     49-005-0004  Nonattainment......................  Nonattainment......................     45 (2013-2015)
Utah...............................  Salt Lake.............  Salt Lake City........     49-035-3006  Nonattainment......................  Nonattainment......................                 38
Utah...............................  Salt Lake.............  Salt Lake City........     49-035-3010  Nonattainment......................  Nonattainment......................                 42
Utah...............................  Utah..................  Provo.................     49-049-0002  Nonattainment......................  Nonattainment......................                 29
Utah...............................  Utah..................  Provo.................     49-049-4001  Nonattainment......................  Nonattainment......................     43 (2013-2015)
Utah...............................  Utah..................  Provo.................     49-049-5010  Nonattainment......................  Nonattainment......................                 27
Utah...............................  Weber.................  Salt Lake City........     49-057-0002  Maintenance........................  Nonattainment......................     37 (2013-2015)
Montana............................  Lewis and Clark.......  ......................     30-049-0026  Maintenance........................  Maintenance........................                 37
Utah...............................  Davis.................  Salt Lake City........     49-011-0004  Nonattainment......................  Maintenance........................                 34
Utah...............................  Weber.................  Salt Lake City........     49-057-1003  Not discussed......................  Maintenance........................     35 (2011-2013)
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
\a\ A blank cell in the column for nonattainment area indicates that the monitor is not located in an area currently designated nonattainment for the 2006 PM2.5 NAAQS.
\b\ Although EPA's 2012 PM2.5 Transport Memo did not identify the Pinal County, Arizona monitor as either a nonattainment or maintenance receptor in the 2009-2013 data, we are evaluating it
  here as a nonattainment receptor because it was identified as such in the California Transport Plan.

                                  Table 4--EPA List of Potential Maintenance Receptors for the 2012 Annual PM2.5 NAAQS
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                2014-2016 design
              State                       County          AQS site ID    CARB receptor type   EPA receptor type    EPA receptor type    value ([micro]g/
                                                                          (2012-2014 data)    (2017 projection)    (2025 projection)         m\3\)
--------------------------------------------------------------------------------------------------------------------------------------------------------
Idaho \a\........................  Shoshone...........     16-079-0017  Nonattainment (13.1  Maintenance (Avg.    Maintenance (Max.                 11.9
                                                                         [micro]g/m\3\).      12.43 [micro]g/      12.22 [micro]g/
                                                                                m\3\).               m\3\).

Pennsylvania.....................  Allegheny..........     42-003-0064  Not discussed......  Maintenance (Max.    Attainment (Max.                  12.8
                                                                                12.16 [micro]g/      11.65 [micro]g/
                                                                                m\3\).               m\3\).
--------------------------------------------------------------------------------------------------------------------------------------------------------
\a\ CARB identified the monitor in Lemhi County, Idaho (AQS ID 16-059-0004) as a nonattainment receptor based on a 2012-2014 design value of 12.1
  [micro]g/m\3\. The EPA's modeling for the 2012 PM2.5 NAAQS Transport Memo projects this monitor to be attaining and maintaining the NAAQS in both 2017
  (maximum design value of 11.79 [micro]g/m\3\) and 2025 (maximum design value of 11.65 [micro]g/m\3\). Its 2014-2016 design value is 12.4 [micro]g/
  m\3\.

4. Evaluation of California Control Measures
    We discuss California's control measures before presenting our
analysis for transport prongs 1 and 2 for each NAAQS because such
discussion provides a common basis for evaluating the California
emissions component of CARB's weight of evidence analysis. Also, for
three precursors, we incorporate our evaluation of California's
emissions and regulatory programs in sections II.B and II.D of this
proposed rule for NOX and VOC (for the 2008 ozone NAAQS) and
SOX (for the 2010 SO2 NAAQS), respectively, given
their roles as precursors to ambient PM2.5.
    We agree with CARB's general conclusions: That California emissions
from stationary sources are subject to stringent limits for
PM2.5 and its precursors, such as those for NOX
and SOX; that California has a long history of reducing
emissions through motor vehicle and fuel standards; and that
California's State and local measures will continue to reduce the
potential for California emissions to contribute significantly to
nonattainment, or interfere with maintenance, of the 2006 24-hour
PM2.5 or 2012 annual PM2.5 NAAQS in any other
state. This is based on our review of the state and local measures
cited in the California Transport Plan that limit the emissions of
PM2.5 and its precursor pollutants and of the applicable
California emission trends, which are generally decreasing.
    For direct PM2.5 emissions, the California Transport
Plan cites examples of State and local rules that limit the emission of
particulate matter (PM), which includes direct PM2.5, and
cites to the EPA actions approving such measures into the SIP.\101\
These include emission standards and test procedures for heavy-duty
engines and vehicles, passenger cars, light duty trucks, and medium
duty vehicles; in-use diesel standards for heavy-duty trucks, buses,
drayage trucks, and off-road vehicles; and inspection and maintenance
programs. We affirm that these measures limit the emission of PM and
have been approved into the California SIP.\102\
---------------------------------------------------------------------------

    \101\ California Transport Plan, p. 8.
    \102\ See, for example, 77 FR 20308 (April 4, 2012), approving
Title 13 of the California Code of Regulations (CCR) section 2025,
commonly referred to as CARB's Truck and Bus Rule, into the
California SIP.
---------------------------------------------------------------------------

    The California Transport Plan also includes examples of air
district measures for area sources such as those for open burning in
South Coast and Imperial County, agricultural burning in Sacramento
Metro and Imperial County, fugitive dust in Mojave Desert, and
agricultural sources in San Joaquin Valley. We similarly affirm that
these measures limit the emission of PM and have been approved into the
California SIP.\103\ More broadly, the California Transport Plan refers
to control measures that apply to a range of pollutants emitted by
refineries, manufacturing facilities, cement plants, refinishing
operations, electricity generation and biomass facilities, boilers, and
generators.\104\ As a general matter, we affirm that there are many
SIP-approved rules for such sources that limit the emission of PM and
its precursors.
---------------------------------------------------------------------------

    \103\ See, for example, 66 FR 36170 (July 11, 2001), approving
Imperial County APCD Rule 421 (``Open Burning,'' amended September
14, 1999) into the California SIP.
    \104\ California Transport Plan, p. 6.
---------------------------------------------------------------------------

    Per our review of the EPA's emissions trends data, from 2000 to
2016, total statewide PM2.5 emissions, excluding wildfires
and prescribed fires, decreased by 75 percent, resulting in 2016
emissions of 99,016 tpy.\105\ As discussed in section II.B.5 of this
proposed rule, we estimate that California emissions will be reduced
from 2011 to 2017 by 535 tpd of NOX (28 percent decrease
from 2011) and 302 tpd of VOC (13 percent decrease from 2011). On a
longer timeline, from 2000 to 2016, California NOX and VOC
emissions have decreased by 66 percent and 54 percent, respectively.
For SO2, total statewide emissions have decreased by 75
percent from 2000 to 2016. Thus, emissions of each of these pollutants
has decreased substantially in response to California State and local
control measures, as well as federal measures for sources outside
California's regulatory authority.
---------------------------------------------------------------------------

    \105\ 1990-2016 emission inventory spreadsheets of statewide
emission trends, included in the docket to this rulemaking and
entitled ``1990-2016 State Tier 1 Annual Average Emission Trends--
RIX Analysis.xls.'' Additional emissions trends data are available
at: https://www.epa.gov/air-emissions-inventories/air-pollutant-emissions-trends-data.
---------------------------------------------------------------------------

5. Evaluation for the 2006 24-Hour PM2.5 NAAQS
    We summarize our evaluation of the areas encompassing the 18
nonattainment receptors identified in Table 3 and group them into three
geographic bins (i.e., Arizona, the Northern Rocky Mountains, and Utah)
based on the nature of the emission sources affecting the receptors. We
then summarize our evaluation of the areas encompassing the three
maintenance receptors identified in Table 3 and group them by the two
relevant states. The EPA's PM2.5 Transport TSD in the docket
for this proposed rule contains our more detailed analyses for
interstate transport prongs 1 and 2.
i. Evaluation for Significant Contribution to Nonattainment (Prong 1)
    CARB discussed the Pinal County, Arizona receptor, which is known
as the Cowtown monitor. This receptor is in the West Central Pinal
PM2.5 nonattainment area, approximately 240 km east of the
California border. The Cowtown area is surrounded by mountain ranges
with open-ended valleys that could allow transport of air pollution
from the west. The area's population has grown by 40 percent from 2005
to 2014 and the VMT has grown by 10 percent between 2005 and 2011. Most
of the exceedances of the 2006 24-hour PM2.5 NAAQS at the
Cowtown monitor did not occur during high wind conditions, indicating
that they were likely due to local rather than transported sources,
particularly local feedlots and geologic soil, based on speciated
ambient PM2.5 data. The 24-hour PM2.5
concentrations at this receptor were the highest in Arizona, yet the
PM2.5 monitor in Yuma, Arizona, along the California border,
recorded

lower concentrations of 15-19 [micro]g/m\3\--well below 35 [micro]g/
m\3\.
    For the Northern Rocky Mountains, which herein includes
nonattainment receptors in Idaho, Montana, Oregon, and the Cache County
portion of Utah, we evaluated nine nonattainment receptors. The
receptors in Idaho and Montana are 360-740 km from California while
those in Oregon are 25-255 km from California. All nine are separated
from California by various mountain ranges. Locally, the receptors are
surrounded by mountains that in some cases rise several thousand feet
above the mountain basins, forming a topographical barrier to
PM2.5 transport and often trapping PM2.5
pollution near the surface during wintertime temperature inversions.
For example, the receptors in Franklin County, Idaho and Cache County,
Utah are surrounded by the Wasatch-Cache, Bear River, Monte Cristo, and
Wellsville mountain ranges that rise 3,000 to 5,000 feet above the
valley floor. These areas tend to have small populations with VMT
increases or decreases of 20 percent or less from 2005 to 2011.
    The highest 24-hour PM2.5 concentrations in each area
are generally observed in winter, with certain receptors, representing
counties in Idaho (Lemhi and Shoshone), Montana (Silver Bow), and
Oregon (Lake and Lane), that appear to have been affected by wildfire
in summer or fall. The PM2.5 concentrations at IMPROVE
monitors nearest each of these receptors, including IMPROVE monitors
between California and the receptors, were generally low when elevated
PM2.5 concentrations were recorded at the receptors, in
winter. Where available, limited chemical speciation and meteorological
data during cold PM2.5 episodes indicate that transport of
air pollution from the periphery of such areas is limited and that
PM2.5 is formed from local emission sources through
secondary formation of PM2.5. Residential wood burning,
especially during winter inversions, is considered the primary
contributor to 24-hour PM2.5 exceedances. Additional sources
contributing to such exceedances vary by area and may include mobile
sources and agricultural activities (e.g., open burning).
    For Utah, we evaluated seven nonattainment receptors that are
either in the Salt Lake City or Provo nonattainment area for the 2006
PM2.5 NAAQS. Both areas are valleys bordered to the east by
the Wasatch Mountains, to the west by the Stansbury and Promontory
Mountains and the Great Salt Lake for Salt Lake City, and by the
Oquirrh Mountains and Utah Lake for Provo. While they are designated
separately, the EPA has determined that the two areas share an airshed.
These areas are about 700 km from the California border and separated
from California by the Sierra Nevada mountain range and the Great
Basin, a large area comprised of depressions and flats scattered
between smaller mountain ranges in Nevada and Utah. Approximately 80
percent of the population of Utah resides in the counties with
nonattainment receptors identified in CARB's and the EPA's analyses,
with county population increases ranging from 11-26 percent from 2005
to 2014 and county VMT changes ranging from a 62 percent decrease in
Weber County to a 116 percent increase in Box Elder County from 2005 to
2011.
    The highest 24-hour PM2.5 concentrations in these two
nonattainment areas primarily occur during winter, with occasional
spikes in other seasons. IMPROVE monitors between California and the
Salt Lake City and Provo nonattainment areas, including Bryce Canyon
and Zion National Parks in Utah and Jarbidge Wilderness Area in Nevada,
recorded their highest 24-hour PM2.5 concentrations in
summer, and their concentrations were generally low when elevated
PM2.5 concentrations were recorded at the Salt Lake City and
Provo receptors, in winter.\106\ Most of the ambient PM2.5
in the urban portions of these nonattainment areas is generated locally
and trapped during winter inversions. Transport between the Salt Lake
City and Provo areas can occur during these inversions, as there is a
gap in the mountains separating these areas below their average
inversion heights.
---------------------------------------------------------------------------

    \106\ States' contributions to the best and worst visibility
days at IMPROVE monitors were modeled to address requirements of the
EPA's regional haze rule. 64 FR 35714 (July 1, 1999), and later
revised at 82 FR 3078 (January 10, 2017). The California Transport
Plan notes that while the percentage of contributions from
California are highest for the worst visibility days at these
IMPROVE monitors, these days occurred during summer months and would
not, therefore, affect winter exceedances at the receptors in Utah.
California Transport Plan, p. A-54 and Appendix E.1. The modeling
data are available at: http://vista.cira.colostate.edu/TSS/Results/HazePlanning.aspx.
---------------------------------------------------------------------------

    We have reviewed the information compiled and presented in the
California Transport Plan, including distance of relevant receptors
from California; intervening terrain; potential wildfire effects;
chemical speciation data; local topography; the effect of local
emission sources, particularly residential wood burning and, in certain
cases, other sources (e.g., mobile sources, agricultural activities),
on wintertime exceedances; and regional background levels represented
by IMPROVE data. We have reviewed California's emissions and emission