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Federal Register / Vol. 86, No. 150 / Monday, August 9, 2021 / Proposed Rules
EPA.20 On September 30, 2020, NDEP
submitted the 2020 Ozone Maintenance Plan Revision to the EPA as a revision to the Clark County portion of the Nevada SIP.21 The 2020 Ozone Maintenance Plan Revision also includes a technical support document appendix A of the plan revision and documentation of the public review process appendix B of the plan revision.
Through the 2020 Ozone Maintenance Plan Revision, Clark County DES is updating the emissions projections for the ozone maintenance plan horizon year of 2022 based on the latest available emissions models, vehicle mix and speed data, and transportation activity projections and is revising the budgets for 2022 to reflect the updated projections for that year and to include a reduced safety margin compared to the corresponding budgets from the 2018
Ozone Maintenance Plan Revision. The 2020 Ozone Maintenance Plan Revision also presents a new emissions inventory for year 2017 that provides the basis to evaluate the new budgets with respect to continued attainment of the 2008
ozone NAAQS and progress towards attainment of the 2015 ozone NAAQS in Las Vegas Valley.

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IV. Procedural Requirements for Adoption and Submittal of SIP
Revisions Sections 110a1 and 2 and 110l of the CAA require a state to provide reasonable public notice and opportunity for public hearing prior to the adoption and submittal of a SIP or SIP revision. To meet this requirement, every SIP submittal should include evidence that adequate public notice was given and an opportunity for a public hearing was provided consistent with the EPAs implementing regulations in 40 CFR 51.102.
The Clark County Board of County Commissioners and NDEP have satisfied applicable statutory and regulatory requirements for reasonable public notice and public hearing prior to adoption and submittal of the 2020
Ozone Maintenance Plan Revision. In the September 30, 2020 SIP submittal,22
20 Clark County Board of County Commissioners Meeting, Meeting Summary, October 16, 2018, 14
and 15.
21 Letter dated September 25, 2020, from Greg Lovato, Administrator, NDEP to Elizabeth Adams, Director, Air Division, EPA Region IX, submitted electronically on September 30, 2020 with enclosures.
22 Appendix B provides evidence that reasonable notice of a public hearing was provided to the public and that a public hearing was conducted prior to adoption. Specifically, notice of the availability of, and opening of a 30-day comment period on the draft ozone maintenance plan
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Clark County DES provided evidence of the required public notice and opportunity for public comment prior to the August 18, 2020 public hearing and adoption of the 2020 Ozone Maintenance Plan Revision. Therefore, we find that the submittal of the 2020
Ozone Maintenance Plan Revision meets the procedural requirements for public notice and hearing in CAA
sections 110a and 110l and 40 CFR
51.102.
V. The EPAs Evaluation of the 2020
Ozone Maintenance Plan Revision Clark County DES and NDEP
submitted the 2020 Ozone Maintenance Plan Revision to fulfill commitments made in connection with the EPAs conditional approval of the 2018 Ozone Maintenance Plan Revision to reduce the safety margin allocations in the budgets to ensure that the Clark County ozone SIP will not interfere with RFP or attainment of the 2008 and 2015 ozone NAAQS consistent with CAA section 110l. As described further below, we have reviewed the 2020 Ozone Maintenance Plan Revision for compliance with the relevant requirements for maintenance plans under CAA section 175A and for noninterference under CAA section 110l, and we have evaluated the budgets in the 2020 Ozone Maintenance Plan Revision for compliance with the budget adequacy criteria in 40 CFR
93.118e.
A. Emissions Inventories The 2020 Ozone Maintenance Plan Revision includes inventories of emissions of ozone precursors VOC and NOX for years 2017 and 2022. The 2017
inventory provides estimates of actual emissions that occurred in that year.
Clark County DES selected 2017 as the base year for the 2020 Ozone Maintenance Plan Revision for the following reasons: It is the most recent year for which National Emissions Inventory 23 NEI emissions estimates were available at the time the plan was being developed; it is an attainment year for the 2008 ozone NAAQS; and it is the base year for SIP planning purposes for the 2015 ozone NAAQS. Clark County DES used the 2017 inventory to revise the 2022 emissions inventory from the 2018 Ozone Maintenance Plan Revision revision was published on June 25, 2020, on the Countys webpage. No comments were submitted.
23 The NEI is a comprehensive and detailed estimate of air emissions of criteria pollutants, criteria precursors, and hazardous air pollutants from air emissions sources. The NEI is released every three years based primarily upon data provided by State, Local, and Tribal air agencies for sources in their jurisdictions and supplemented by data developed by the EPA.

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based on the latest methods and planning assumptions.
As a general matter, base year emissions inventories must be 1
consistent with the EPAs most recent guidance on emissions inventories available at the time, 2 comprehensive, including emissions from stationary point sources, area sources, nonroad mobile sources, and on-road mobile sources, and 3 based on actual ozone season data i.e., summertime emissions.24
The 2017 year inventory in the 2020
Ozone Maintenance Plan Revision is comprehensive in that it includes estimates of summertime average weekday VOC and NOX emissions from all of the relevant source categories, which the plan divides among point sources,25 nonpoint sources,26
commercial aviation, federal aviation i.e., Nellis Air Force Base, on-road mobile, nonroad mobile, and biogenic 27
sources.28 For comparison, the 2018
Ozone Maintenance Plan Revision did not include a 2017 inventory, but emissions for 2017 can be interpolated from 2015 and 2022 emissions.
Appendix A to the 2020 Ozone Maintenance Plan Revision contains source-specific descriptions of emission calculation procedures and sources of input data used for the update.
Table 2 below compares the 2017
inventory from the 2020 Ozone Maintenance Plan Revision with the corresponding interpolated inventory from the 2018 Ozone Maintenance Plan Revision. As shown in Table 2, the change in the 2017 inventory in the 2020 Ozone Maintenance Plan Revision is primarily due to the update to the onroad mobile source category and the nonroad source category as well as a change in the methodology for biogenic emissions.
24 In Clark County, Nevada, the highest ambient ozone concentrations generally occur during the months of the year when the highest temperatures occurtypically from May through September. For SIP planning purposes, Clark County has selected weekdays in the month of July as the basis to estimate typical summertime weekday emissions.
25 The 2020 Ozone Maintenance Plan Revision uses the term, point sources, to refer to those stationary source facilities that are required to report their emissions to Clark County DES or NDEP.
26 The 2020 Ozone Maintenance Plan Revision uses the term, nonpoint sources, to refer to those stationary and area sources that fall below point source reporting levels and that are too numerous or small to identify individually.
27 For the 2020 Ozone Maintenance Plan Revision, biogenic sources include the following:
Agricultural crops; lawn grass; forests that produce isoprene, monoterpene, alpha-pinene, and other VOC emissions; and soils that generate trace amounts of NOX.
28 See Table 21 in the 2020 Ozone Maintenance Plan Revision.

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