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Federal Register / Vol. 86, No. 114 / Wednesday, June 16, 2021 / Rules and Regulations
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51.164, the EPA has determined, as explained in our proposal, that the ADEQs program now meets the relevant requirements for a minor NSR program.
In response to the commenters specific concerns here, we consider the two PM2.5 nonattainment areas in ArizonaNogales and West Central Pinal. Regarding the Nogales area, where the ADEQ has minor NSR
permitting jurisdiction, the ADEQs 2020 Minor NSR submittal explains that the Nogales PM2.5 nonattainment area was found to have attained the 2006 24hour PM2.5 NAAQS in 2017. 14 Further, while the ADEQs minor NSR program does not specifically regulate VOC as a PM2.5 precursor, minor sources of VOC
are, in fact, regulated by the ADEQs minor NSR program at a source-wide permitting threshold of 20 tons per year.
The 2020 Minor NSR submittal contains an analysis showing that this permitting threshold is expected to cover at least 86% of VOC emissions in areas subject to ADEQ permitting jurisdiction.15 For the West Central Pinal PM2.5
nonattainment area, the Pinal County Air Quality Control District, not the ADEQ, has primary permitting jurisdiction for minor sources.
Accordingly, the ADEQs minor NSR
permitting program generally does not apply in the West Central Pinal PM2.5
nonattainment area.16
Although the commenters mention certain types of operations that may emit ammonia and VOCs, the commenters do not provide information or explanation that demonstrates that the ADEQs regulating those pollutants as precursors to PM2.5 in the PM2.5
nonattainment areas under the ADEQs jurisdiction as part of the ADEQs minor NSR program is necessary to achieve the PM2.5 NAAQS in any such areas. As explained above, the only PM2.5
nonattainment area where the ADEQ
has primary jurisdiction for minor sources, the Nogales area, is already attaining the PM2.5 NAAQS. Moreover, in addition to regulating direct PM2.5
emissions, the ADEQs minor NSR
program regulates emissions of NOX and SO2 as PM2.5 precursors and regulates 14 2020 Minor NSR submittal at 19; section 4.4.3.2. See also 82 FR 21711 May 10, 2017 EPA
determination of attainment by the attainment date.
15 2020 Minor NSR submittal at 16; Table 42.
16 We also note that the ADEQs March 29, 2019
SIP revision related to ammonia as a PM2.5
precursor provides results from a 2010 ADEQ study that determined the speciation of PM2.5 emissions in the West Central Pinal nonattainment area. The study showed that 90% of PM2.5 emissions in the West Central Pinal nonattainment area originate from direct PM2.5 sources, and less than 10% from PM2.5 precursors. March 29, 2019 SIP submittal at 11; Table 33.

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VOC emissions in general. In light of the information described above, we find that the ADEQs determination to not regulate sources of ammonia and VOCs as PM2.5 precursors in its minor NSR
program in the PM2.5 nonattainment areas under its jurisdiction is reasonable and not necessary to ensure that the PM2.5 NAAQS are achieved.
The commenters also indicate that the EPAs approval of the 2020 Minor NSR
submittal conflicts with the requirement in CAA section 110l that the EPA
shall not approve a revision of a plan if the revision would interfere with any applicable requirement concerning attainment and reasonable further progress. . .or any other applicable requirement of this chapter. Our December 23, 2020 proposed approval contained our analysis that our action met these requirements of CAA section 110l: We have determined that our action on the 201920 NSR submittals would, as described herein, strengthen the applicable SIP. This action is primarily intended to correct numerous deficiencies in the ADEQs NSR
program and provides other revisions to enhance and update the program.
Accordingly, this action will not interfere with attainment and reasonable further progress, or any other applicable requirement. 17 The commenters did not address this analysis or explain how this action to correct deficiencies in the ADEQs minor NSR program will interfere with any applicable requirement concerning attainment and reasonable further progress or any other CAA requirement in the PM2.5
nonattainment areas under the ADEQs jurisdiction that are of concern to the commenter. This action strengthens the overall SIP and does not relax any SIP
requirements related to attaining the PM2.5 NAAQS in Arizona.
The commenters make the related argument that the ADEQs SIP revision does not satisfy section 2.2d of Appendix V to 40 CFR part 51 because it does not regulate VOCs and ammonia as precursors to PM2.5 and therefore interferes with attainment of the PM2.5
NAAQS in areas under ADEQs jurisdiction that are designated nonattainment for PM2.5.18 As described above, the 201920 SIP submittals contain sufficient information to 17 85

FR 83868, 83876 Dec. 23, 2020.
18 The commenters reference the portion of section 2.2d that requires SIP submittals to demonstrate that the national ambient air quality standards, prevention of significant deterioration increments, reasonable further progress demonstration, and visibility, as applicable, are protected if the plan is approved and implemented. See 40 CFR part 51, Appendix V, section 2.2d.

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support our conclusion that the ADEQs decision not to specifically regulate VOC and ammonia as PM2.5 precursors for its minor NSR program is acceptable and will not interfere with attainment of the PM2.5 NAAQS.
Lastly, in response to the commenters argument that the ADEQ should have included a modeling demonstration relating to ammonia and VOC as PM2.5
precursors to meet the requirements of section 2.2e of Appendix V to 40 CFR
part 51, the commenters have not accurately characterized these requirements.19 We do not interpret section 2.2e of Appendix V to require that every SIP submittal contain a modeling demonstration, as implied by the commenters. Instead, when a modeling demonstration is necessary and is therefore included in a submittal to support the SIP revision, then the submittal must also contain the underlying modeling information outlined in section 2.2e. We find that section 2.2e of Appendix V is not applicable to the 2020 Minor NSR
submittal because modeling was not used to support this SIP revision nor was a modeling demonstration required in this instance.
Comment: The commenters consider the ADEQs minor NSR thresholds of one-half the significant emission rates SERs in the PSD program 20 to be arbitrary and unsupported by modeling or other evidence demonstrating protection of the NAAQS, in violation of CAA section 110l and sections 2.2d and e in Appendix V to 40 CFR part 51. The commenters argue that merely comparing the percentage of emissions regulated by the ADEQs program to other programs does not address whether thresholds are protective of the NAAQS. The commenters assert that the ADEQ misplaced focus on the contributions of current sources in nonattainment areas under its jurisdiction and whether those areas are now violating the NAAQS. Instead, the ADEQ should have focused on ensuring that additional sources or new modifications of existing sources do not jeopardize attainment or maintenance of the NAAQS in the future.
Response: We respectfully disagree with the commenters that the ADEQ has not provided an adequate rationale for 19 Section 2.2e of Appendix V requires that a SIP
submittal include the modeling information required to support the proposed revision, including input data, output data, models used, justification of model selections, ambient monitoring data used, meteorological data used, justification for use of offsite data where used, modes of models used, assumptions, and other information relevant to the determination of adequacy of the modeling analysis.
20 See 40 CFR 51.166b23i.

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