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Federal Register / Vol. 86, No. 183 / Friday, September 24, 2021 / Proposed Rules and projections of motor vehicle emissions, and the percentage of the total attainment plan emissions inventory for the NAAQS at issue that is comprised of motor vehicle emissions. The EPAs rationale for providing for insignificance determinations is described in the July 1, 2004 revision to the Transportation Conformity Rule.248
Transportation conformity trading mechanisms are allowed under 40 CFR
93.124 where a state establishes appropriate mechanisms for such trades.
The basis for the trading mechanism is the SIP attainment modeling that establishes the relative contribution of each PM2.5 precursor pollutant. The applicability of emissions trading between conformity budgets for conformity purposes is described in 40
CFR 93.124c.
The EPAs process for determining the adequacy of a budget consists of three basic steps: 1 Notifying the public of a SIP submittal; 2 providing the public the opportunity to comment on the budget during a public comment period;
and 3 making a finding of adequacy or
inadequacy. The EPA can notify the public by either posting an announcement that the EPA has received SIP budgets on the EPAs adequacy website,249 or through a Federal Register notice of proposed rulemaking when the EPA reviews the adequacy of an implementation plan budget simultaneously with its review and action on the SIP itself.250
2. Summary of the States Submission The 2018 PM2.5 Plan includes budgets for direct PM2.5 and NOX emissions, calculated using annual average daily emissions, for 2017, 2020, and 2023
RFP milestone year, attainment year, and post-attainment quantitative milestone year, respectively.251 The Plan establishes separate direct PM2.5
and NOX subarea budgets for each county, and partial county for Kern County, in the San Joaquin Valley.252
CARB calculated the budgets using EMFAC2014, CARBs latest version of the EMFAC model for estimating emissions from on-road vehicles operating in California that was available at the time of Plan
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development, and the latest modeled vehicle miles traveled and speed distributions from the San Joaquin Valley MPOs from the Final 2017
Federal Transportation Improvement Program, adopted in September 2016.
The budgets reflect annual average emissions because those emissions are linked with the Districts attainment demonstration for the 1997 24-hour PM2.5 NAAQS.
The direct PM2.5 budgets include tailpipe, brake wear, and tire wear emissions but do not include paved road dust, unpaved road dust, and road construction dust emissions.253 The State is not required to include reentrained road dust in the budgets under section 93.103b3 unless the EPA or the State has made a finding that these emissions are significant. Neither the State nor the EPA has made such a finding, but the Plan does include a discussion of the significance/
insignificance factors for re-entrained road dust.254 The budgets included in the 2018 PM2.5 Plan for purposes of the 1997 24-hour PM2.5 NAAQS are shown in Table 8.

TABLE 8MOTOR VEHICLE EMISSION BUDGETS FOR THE SAN JOAQUIN VALLEY FOR THE 1997 24-HOUR PM2.5 NAAQS
Annual average, tpd 2017
RFP year
County PM2.5
Fresno
Kern
Kings
Madera
Merced
San Joaquin
Stanislaus
Tulare

2020
Attainment year NOX

0.9
0.8
0.2
0.2
0.3
0.7
0.4
0.4

PM2.5
28.5
28.0
5.8
5.3
10.7
14.9
11.9
10.8

2023
Post-attainment year
NOX
0.9
0.8
0.2
0.2
0.3
0.6
0.4
0.4

PM2.5
25.3
23.3
4.8
4.2
8.9
11.9
9.6
8.5

NOX
0.8
0.7
0.2
0.2
0.3
0.6
0.4
0.4

15.1
13.3
2.8
2.5
5.3
7.6
6.1
5.2

Source: 2018 PM2.5 Plan, Appendix D, Table 31. Budgets are rounded to the nearest tenth of a ton.

The State did not include budgets for VOC, SO2, or ammonia. As discussed in section IV.B of this preamble, the State submitted a PM2.5 precursor demonstration documenting its conclusion that control of these precursors would not significantly contribute to attainment of the 1997 24hour PM2.5 NAAQS, and the EPA is proposing to approve the precursor demonstration. Therefore, if the EPA
approves the demonstration, the State would not be required to submit budgets for these precursors. The State included a discussion of the significance/
insignificance factors for ammonia, SO2, FR 40004.
CFR 93.118f1.
250 40 CFR 93.118f2.
251 2018 PM
2.5 Plan, Appendix D, Table 31.

and VOC to demonstrate a finding of insignificance under the transportation conformity rule.255
In the submittal letter for the 2018
PM2.5 Plan, CARB requested that the EPA limit the duration of the approval of the budgets to the period before the effective date of the EPAs adequacy finding for any subsequently submitted budgets.256
Conformity Trading Mechanism The 2018 PM2.5 Plan also includes a proposed trading mechanism for transportation conformity analyses that would allow future decreases in NOX

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CFR 93.124c and d.
PM2.5 Plan, Appendix D, D122 and D

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emissions from on-road mobile sources to offset any on-road increases in direct PM2.5 emissions. The State is proposing to use a 2 to 1 NOX to PM2.5 ratio for the 1997 24-hour PM2.5 NAAQS. This ratio was derived by performing a sensitivity analysis based on a 30
percent reduction of NOX or PM2.5
emissions and calculating the corresponding effect on design values at sites in Bakersfield and Fresno.
To ensure that the trading mechanism does not affect the ability of the San Joaquin Valley to meet the NOX budget, the NOX emissions reductions available to supplement the PM2.5 budget would 255 40

CFR 93.109f.
dated May 9, 2019, from Richard W.
Corey, Executive Officer, CARB, to Mike Stoker, Regional Administrator, EPA Region 9, 3.
256 Letter
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