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Federal Register / Vol. 86, No. 150 / Monday, August 9, 2021 / Proposed Rules Plan Revision. As noted in section V.A
of this document, Clark County DES
developed the revised budgets using the latest emissions model MOVES2014b available at the time the 2020 Ozone Maintenance Plan Revision was being developed, and the most recent travel activity projections provided by the Nevada Department of Transportation
and RTC. Therefore, we find that the revised budgets reflect the most recent planning forecasts and are based on the most recent emission factor data and approved calculation methods.
A state may choose to allocate all or a portion of the safety margin 38 under the EPA transportation conformity rule so long as such margins are explicitly quantified in the applicable plan and
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are shown to be consistent with attainment or maintenance of the NAAQS whichever is relevant to the particular plan.39 For the 2020 Ozone Maintenance Plan Revision, Clark County DES allocated a 3 tons per day tpd safety margin for NOX and VOC in 2022 to the projected on-road emissions estimates for NOX and VOC.

TABLE 4CLARK COUNTY YEAR 2022 OZONE MOTOR VEHICLE EMISSION BUDGETS
County-wide, average summer weekday, tpd 2018 Ozone maintenance plan revision
Source category NOX
On-Road Mobile
Transportation Conformity Safety Margins
Budgets

2020 Ozone maintenance plan revision
VOC

27.02
59.72
86.74

NOX

17.12
35.84
52.96

29.16
3.00
32.16

VOC
20.92
3.00
23.92

lotter on DSK11XQN23PROD with PROPOSALS1

Sources: 2018 Ozone Maintenance Plan Revision, Table 31; 2020 Ozone Maintenance Plan Revision, Table 31.

conditionally approved for use in transportation conformity determinations.

attainment of the NAAQS for which VOC and NOX are precursors, namely, the 2008 and 2015 ozone NAAQS.41
In our conditional approval of the 2018 Ozone Maintenance Plan Revision, we determined that if the 2018 Ozone Maintenance Plan Revision were revised to reduce the safety margin allocations to the budgets such that total estimated emissions in 2022 with the allocations would not exceed actual emissions in year 2017, then the updated budgets would not interfere with reasonable further progress or attainment of the 2008 and 2015 ozone NAAQS.

As documented in a April 20, 2021
memorandum to the docket for this rulemaking, we find that the budgets in the 2020 Ozone Maintenance Plan Revision meet each adequacy criterion.40 In short, we reviewed the budgets in the 2020 Ozone Maintenance Plan Revision and found that they are consistent with the revised maintenance demonstration from the 2018 Ozone Maintenance Plan Revision; are based on control measures that have already been adopted and implemented; and meet all other applicable statutory and regulatory requirements including the adequacy criteria in 40 CFR
93.1118e4 and 5. Therefore, we are proposing to approve the 2022 budgets in the 2020 Ozone Maintenance Plan Revision. If we finalize our approval of the revised budgets in the 2020 Ozone Maintenance Plan Revision, as proposed, they will replace the corresponding budgets for the 1997
ozone NAAQS from the 2018 Ozone Maintenance Plan Revision that we previously found adequate and
In relevant part, CAA section 110l provides that the EPA shall not approve a SIP revision that would interfere with any applicable requirement concerning attainment or RFP of any of the NAAQS
or any other applicable requirement of the CAA. The 2018 Ozone Maintenance Plan Revision established budgets that are larger than those that were previously approved from the 2011
Ozone Maintenance Plan. Thus, approval of the 2018 Ozone Maintenance Plan Revision accommodated a higher level of VOC
and NOX emissions from on-road mobile source emissions than would otherwise be allowed under the previous budgets.
In our approval of the 2018 Ozone Maintenance Plan Revision, we evaluated the higher level of VOC and NOX emissions with respect to the potential for interference with RFP and
As noted in Section II.B of this document, in 2012, the EPA designated all the hydrographic areas within the State of Nevada as unclassifiable/
attainment for the 0.075 ppm 2008
ozone NAAQS based on ambient ozone concentration data for years 2009
2011.42 After the original designation, the 8-hour ozone design values within Clark County exceeded the 2008 ozone
38 In this context, safety margin means the amount by which the total projected emissions from all sources of a given pollutant are less than the total emissions that would satisfy the applicable requirements for reasonable further progress, attainment or maintenance. With respect to the 2020 Ozone Maintenance Plan Revision, the safety margin is the difference between the projected emissions in 2022 of NOX and VOC and the actual emissions of NOX and VOC in the 2008 attainment year as updated in the 2018 Ozone Maintenance Plan Revision. The anthropogenic emissions i.e., excluding biogenic emissions of NOX and VOC in 2008 were approximately 178 tons per day tpd and 157 tpd, respectively. The 2020 Ozone Maintenance Plan Revision continues to provide for maintenance of the 1997 ozone NAAQS because the anthropogenic emissions of NOX and VOC in 2022
including the ERCs and transportation conformity
safety margins would be approximately 114 tpd and 122 tpd, respectively, which is substantially less than the emissions in the attainment year 2008 for the 1997 ozone NAAQS.
39 See 40 CFR 93.124a.
40 Memorandum dated April 20, 2021, from Karina OConnor, Air Planning Office, EPA Region IX, Adequacy Documentation for Plan Motor Vehicle Emission Budgets in August 2020 Clark County Revision to Ozone Maintenance Plan. This memorandum has been uploaded to the docket EPAR09OAR20210368 for this rulemaking.
41 As a general matter, VOC and NO are also X
considered precursors for course particulate matter PM10 and fine particulate matter PM2.5. In our conditional approval of the 2018 Ozone Maintenance Plan Revision, we concluded that the revised budgets, even with the substantial safety margins, would not interfere with attainment or
maintenance of the PM10 or PM2.5 NAAQS. 84 FR
33035, at 3304333044 July 11, 2019 proposed rule, finalized at 84 FR 44699 August 27, 2019.
Clark County is designated as attainment for the PM10 NAAQS and unclassifiable/attainment for the PM2.5 NAAQS. 40 CFR 81.329. In this document, we are proposing approval of budgets that have been revised to substantially reduce the safety margins, and thus, the potential for interference with attainment or maintenance of the PM10 or PM2.5
NAAQS is even less than it was previously. As such, we find that approval of the 2020 Ozone Maintenance Plan Revision would not interfere with attainment or maintenance of the PM10 or PM2.5 NAAQS in Clark County.
42 Letter dated December 9, 2011, from Jared Blumenfeld, Regional Administrator, EPA Region IX, to Brian Sandoval, Governor, State of Nevada.

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