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Federal Register / Vol. 86, No. 150 / Monday, August 9, 2021 / Proposed Rules TABLE 32022 CLARK COUNTY OZONE PRECURSOR EMISSION INVENTORYContinued County-wide, average summer weekday, tons per day NOX emissions 2020 Ozone maintenance plan revision
Source category
VOC emissions
2018 Ozone maintenance plan revision
2020 Ozone maintenance plan revision
2018 Ozone maintenance plan revision
Nonpoint source
Commercial aviation
Federal aviation
On-road mobile
Nonroad mobile
Biogenic
Emission reduction credits
Transportation conformity safety margins

7.57
13.08
1.97
29.16
24.93
2.43
22.23
3.00

5.04
17.42
2.26
27.02
17.50
5.00
22.23
59.72

62.58
1.73
0.82
20.92
26.71
362.61
0.43
3.00

59.49
2.95
0.95
17.12
28.52
132.00
0.43
35.84

Total

116.46

168.45

484.92

280.02

Sources: 2018 Ozone Maintenance Plan Revision, Tables 21, 22 and 31; 2020 Ozone Maintenance Plan Revision, Tables 21, 22 and 3

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1.

As shown in Table 3, emissions for 2022 in the 2020 Ozone Maintenance Plan Revision are similar to the corresponding emissions in the 2018
Ozone Maintenance Plan Revision except for biogenic emissions. Similar to the comparison of the emission inventories for the year 2017, differences are again primarily due to the updates to the on-road mobile source category, the nonroad source category, and the change in the methodology for biogenic emissions.
The on-road mobile source emission estimates in the 2020 Ozone Maintenance Plan Revision reflect the most recent published data concerning vehicle registration data, vehicle miles traveled VMT temporal distribution, VMT mix profiles, vehicle speeds, and travel demand forecasts from RTC.33
Based on our review of the methods, assumptions, and data sources, as described in Appendix A to the 2020
Ozone Maintenance Plan Revision, we find that the Clark County DES
estimates for 2017 and 2022 for the various source categories to be based on the best available emissions models and data sources, and thus to provide a reasonable basis upon which to evaluate whether the area will continue to maintain the 1997 ozone NAAQS
through 2022 and whether the revised budgets for 2022 in the 2020 Ozone Maintenance Plan Revision would interfere with RFP or attainment of the 2008 and 2015 ozone NAAQS.
33 Key references used by Clark County DES
include Eastern Research Groups Clark County On-Road Vehicle Classification Study, final report, June 29, 2018, and the Coordinating Research Councils Improvement of Default Inputs for MOVES and SMOKEMOVES, final report, February 2017.

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B. Revised Motor Vehicle Emissions Budgets Section 176c of the CAA requires federal actions in nonattainment and maintenance areas to conform to the SIPs goals of eliminating or reducing the severity and number of violations of the NAAQS and achieving timely attainment of the standards. Conformity to the SIPs goals means that such actions will not: 1 Cause or contribute to violations of a NAAQS, 2 worsen the severity of an existing violation, or 3 delay timely attainment of any NAAQS or any interim milestone.
Under the transportation conformity rule, MPOs in nonattainment and maintenance areas coordinate with state and local air quality and transportation agencies, the EPA, the Federal Highway Administration, and the Federal Transit Administration to demonstrate that an areas regional transportation plans and TIPs conform to the applicable SIP. This demonstration is typically done by showing that estimated emissions from existing and planned highway and transit systems are less than or equal to the budgets contained in all control strategy or maintenance SIPs. Budgets are generally established for specific years and specific pollutants or precursors. Ozone maintenance plans should identify budgets for on-road emissions of ozone precursors NOX and VOC in the area for the last year of the maintenance period. Budgets may also be specified for additional years during the maintenance period.
For budgets to be approvable, they must meet the EPAs adequacy criteria 40 CFR 93.118e4 and 5 and comply with all pertinent SIP
requirements. With respect to maintenance plans, to meet these requirements, the budgets must be consistent with the maintenance plan
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and reflect all the motor vehicle control measures contained in the maintenance demonstration.34 The EPAs process for determining adequacy of a budget consists of three basic steps: 1
Providing public notification of a SIP
submission; 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.35 We will complete the adequacy review of the budgets in the 2020 Ozone Maintenance Plan Revision concurrent with our final action on the 2020 Ozone Maintenance Plan Revision.
The EPA is not required under its transportation conformity rule to find budgets adequate prior to proposing approval of them.36
The 2020 Ozone Maintenance Plan Revision includes revised budgets for VOC and NOX for the last year of the initial maintenance period, i.e., 2022.37
The revised budgets from the 2020
Ozone Maintenance Plan Revision are shown in Table 4 below and compared with the corresponding budgets from the approved 2018 Ozone Maintenance 34 40 CFR 93.118e4iii, iv and v. For more information on the transportation conformity requirements and applicable policies on budgets, please visit our transportation conformity website at: http www.epa.gov/otaq/stateresources/
transconf/index.htm.
35 40 CFR 93.118f2.
36 Under the transportation conformity regulations, the EPA may review the adequacy of submitted motor vehicle emission budgets simultaneously with the EPAs approval or disapproval of the submitted implementation plan.
40 CFR 93.118f2.
37 The 2020 Ozone Maintenance Plan Revision does not revise the 2015 budgets from the 2018
Ozone Maintenance Plan Revision that also included large safety margins; however, we note that, given the passage of time, the 2015 budgets from the 2018 Ozone Maintenance Plan Revision will no longer be used for conformity determinations and thus the failure to reduce the safety margins of the 2015 budgets in the 2018
Ozone Maintenance Plan Revision is acceptable.

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