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Federal Register / Vol. 86, No. 183 / Friday, September 24, 2021 / Proposed Rules
1997 24-hour PM2.5 NAAQS.85 The 2013
base year emissions inventories represent actual annual average emissions of all sources within the nonattainment area, direct PM2.5 and PM2.5 precursors are included in the inventories, and filterable and condensable direct PM2.5 emissions are identified separately.
With respect to future year emissions projections, we have reviewed the growth and control factors and find them acceptable and thus conclude that the future baseline emissions projections, which reflect ongoing emissions reductions from existing i.e., baseline control measures as discussed in section IV.C.2.a, in the SJV
PM2.5 Plan reflect appropriate calculation methods and the latest planning assumptions. Also, as a general matter, the EPA will approve a SIP submission that takes emissions reduction credit for a control measure only where the EPA has approved the measure as part of the SIP. Thus, for example, to take credit for the emissions reductions from newly adopted or amended District rules for stationary sources, the related rules must be approved by the EPA into the SIP. Table 1 of the EPAs Technical Support Document, San Joaquin Valley PM2.5
Plan for the 1997 24-hour PM2.5
NAAQS, August 2021 EPAs 1997
24-hour PM2.5 TSD shows District rules with post-2013 compliance dates that are reflected in the future year baseline inventories, along with information on the EPAs approval of these rules, and shows that stationary source emissions reductions assumed by the SJV PM2.5 Plan for future years are supported by rules approved as part of the California SIP for the San Joaquin Valley. With respect to mobile sources, the EPA has taken action in recent years to approve CARB mobile source regulations into the state-wide portion of the California SIP. We therefore find that the future year baseline projections in the SJV PM2.5 Plan are properly supported by SIP-approved stationary and mobile source measures.86
85 81

FR 84481, 84482.
baseline emissions projections in the 2018
PM2.5 Plan assume implementation of CARBs Zero Emissions Vehicle ZEV sales mandate and greenhouse gas GHG standards. On September 27, 2019, the U.S. Department of Transportation and the EPA the Agencies issued a notice of final rulemaking for the Safer Affordable Fuel-Efficient SAFE Vehicles Rule Part One: One National Program SAFE I that, among other things, withdrew the EPAs 2013 waiver of preemption for the ZEV sales mandate and vehicle GHG standards.
84 FR 51310. See also proposed SAFE rule at 83 FR
42986 August 24, 2018. In response to SAFE I, CARB developed EMFAC off-model adjustment factors to account for anticipated changes in onroad emissions. On March 12, 2020, the EPA
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For these reasons, we are proposing to approve the 2013 base year emissions inventories in the SJV PM2.5 Plan for the 1997 24-hour PM2.5 NAAQS as meeting the requirements of CAA section 172c3 and 40 CFR 51.1008 for purposes of both the Serious area and the CAA section 189d attainment plans. We are also proposing to find that the forecasted inventories in the Plan for the years 2017, 2018, 2019, 2020, and 2023 provide an adequate basis for the BACM, RFP, and the modeled attainment demonstration analyses in the SJV PM2.5 Plan.
B. PM2.5 Precursors 1. Statutory and Regulatory Requirements The composition of PM2.5 is complex and highly variable due in part to the large contribution of secondary PM2.5 to total fine particle mass in most locations, and to the complexity of secondary particle formation processes.
A large number of possible chemical reactions, often non-linear in nature, can convert gaseous NOX, SO2, VOC, and ammonia to PM2.5, making them precursors to PM2.5.87 Formation of secondary PM2.5 may also depend on atmospheric conditions, including solar radiation, temperature, and relative humidity, and the interactions of precursors with preexisting particles and with cloud or fog droplets.88
Under subpart 4 of part D, title I of the CAA and the PM2.5 SIP Requirements Rule, each state containing a PM2.5
nonattainment area must evaluate all PM2.5 precursors for regulation unless, for any given PM2.5 precursor, the state demonstrates to the Administrators satisfaction that such precursor does not contribute significantly to PM2.5 levels informed CARB that the EPA considers these adjustment factors to be acceptable for future use.
See letter dated March 12, 2020 from Elizabeth J.
Adams, EPA Region IX, to Steven Cliff, CARB. On April 30, 2020 85 FR 24174, the Agencies issued a notice of final rulemaking titled: The Safer Affordable Fuel-Efficient SAFE Vehicles Rule for Model Years 20212026 Passenger Cars and Light Trucks SAFE II, establishing the federal fuel economy and GHG vehicle emissions standards based on the August 2018 SAFE proposal. The effect of both SAFE final rules SAFE I and SAFE
II on the on-road vehicle mix in the San Joaquin Valley nonattainment area and on the resulting vehicular emissions is expected to be minimal during the timeframe addressed in this SIP revision.
Therefore, we anticipate the SAFE final rules would not materially change the attainment, RFP, or five percent reductions demonstrations for the 1997 24hour PM2.5 NAAQS in the SJV PM2.5 Plan.
87 Air Quality Criteria for Particulate Matter EPA/600/P99/002aF, EPA, October 2004, Chapter 3.
88 Regulatory Impact Analysis for the Final Revisions to the National Ambient Air Quality Standards for Particulate Matter EPA/452/R12
005, EPA, December 2012, 21.

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that exceed the NAAQS in the nonattainment area.89 The provisions of subpart 4 do not define the term precursor for purposes of PM2.5, nor do they explicitly require the control of any specifically identified PM2.5
precursor. The statutory definition of air pollutant, however, provides that the term includes any precursors to the formation of any air pollutant, to the extent the Administrator has identified such precursor or precursors for the particular purpose for which the term air pollutant is used. 90 The EPA has identified NOX, SO2, VOC, and ammonia as precursors to the formation of PM2.5.91 Accordingly, the attainment plan requirements of subpart 4 apply to emissions of all four precursor pollutants and direct PM2.5 from all types of stationary, area, and mobile sources, except as otherwise provided in the Act e.g., CAA section 189e.
Section 189e of the Act requires that the control requirements for major stationary sources of direct PM10 also apply to major stationary sources of PM10 precursors, except where the Administrator determines that such sources do not contribute significantly to PM10 levels that exceed the standard in the area. Section 189e contains the only express exception to the control requirements under subpart 4 e.g., requirements for RACM and RACT, BACM and BACT, MSM, and new source review NSR. Although section 189e explicitly addresses only major stationary sources, the EPA interprets the Act as authorizing it also to determine, under appropriate circumstances, that regulation of specific PM2.5 precursors from other source categories in a given nonattainment area is not necessary.92
For example, under the EPAs longstanding interpretation of the control requirements that apply to stationary, area, and mobile sources of PM10 precursors in the nonattainment area under CAA section 172c1 and subpart 4,93 a state may demonstrate in a SIP submission that control of a certain precursor pollutant is not necessary because it does not contribute significantly to ambient PM10 levels in the nonattainment area and is not needed for attainment.94
Under the PM2.5 SIP Requirements Rule, a state may elect to submit to the 89 81

FR 58010, 5801758020.
section 302g.
91 81 FR 58010, 58015.
92 Id. at 5801858019.
93 General Preamble, 1353913542.
94 Courts have upheld this approach to the requirements of subpart 4 for PM10. See, e.g., Assoc.
of Irritated Residents v. EPA, et al., 423 F.3d 989
9th Cir. 2005.
90 CAA

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