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Federal Register / Vol. 86, No. 120 / Friday, June 25, 2021 / Rules and Regulations
lotter on DSK11XQN23PROD with RULES1

For a percentage-based NOX
substitution to result in an equivalent ozone reduction, ozone formation must not only be NOX-limited, but also NOX
reductions must be at least as effective at reducing ozone as VOC reductions. In the 2017 Eastern Kern Ozone SIP, CARB
and the District concluded that ozone formation is NOX-limited, but again, they use that term to mean that NOX
reductions are more effective than VOC
reductions. That conclusion was based not only on the weekday-weekend evidence of NOX limitation but also on additional information, as described in the following paragraphs.
The 2017 Eastern Kern Ozone SIP also provides ample documentation that high ozone concentrations in Eastern Kern are mainly due to transport from the San Joaquin Valley SJV to the northwest and sometimes from the South Coast Air Basin SCAB to the southwest.30 Further, NOX and VOC
emissions in the western Kern County portion of the SJV are respectively 2.5
and 8 times those within Eastern Kern;
NOX and VOC emissions in the Los Angeles County portion of SCAB are respectively 10 and 37 times those within Eastern Kern.31 Eastern Kern is downwind of large urban areas, and CARB noted in the 2017 Eastern Kern Ozone SIP the recognized phenomenon that locations downwind of major urban areas have high VOC:NOX ratios and consequently are more sensitive to NOX
reduction than to VOC. The VOC:NOX
ratio of an urban air mass tends to increase as it moves downwind, since there is less input of NOX emissions from combustion sources but continued VOC emissions input from biogenic sources, and also NOX gets preferentially removed by other chemical and physical processes.32 In sources and farther away from the anthropogenic NOX sources, such that low NOX and high ROG
reactivity conditions are prevalent, which is consistent with the region being in a NOX-limited regime, F42. The CARB Staff Report on the Eastern Kern 2017 Ozone Plan see A9 of the Staff Report refers to NOX-limited conditions as discussed in Finlayson-Pitts and Pitts, 1993, p.1093, whose use of NOX-limited is consistent with both the relative and strict senses of the term, but given its context of control of VOCs versus NOX, is more relevant to the relative sense.
30 Eastern Kern 2017 Ozone Plan, Appendix H, H8H15; CARB Staff Report on the Eastern Kern 2017 Ozone Plan, A5.
31 Eastern Kern 2017 Ozone Plan, Appendix H, H20.
32 The VOC:NO ratio increases due to chemical X
conversion to HNO3 and due to the process of deposition to surfaces, which removes NOX in the form of HNO3 from the air more quickly than VOC.
Barbara J. Finlayson-Pitts and James N. Pitts Jr., 1993, Atmospheric Chemistry of Tropospheric Ozone Formation: Scientific and Regulatory Implications, Journal of the Air and Waste Management Association, 43:8, 10911100, https

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Eastern Kern, biogenic VOC emissions are 10 times as high as anthropogenic VOC in 2005 and upwards of 20 times as high during peak biogenic years,33
which also tends to increase the VOC:NOX ratio in Eastern Kern.
EKAPCD estimated biogenic VOC
emissions to be 169 tpd during the period of 2012 through 2020,34 which is over five times the total baseline NOX
inventories used in the RFP
demonstration in Table 3.35 CARB states in the 2017 Eastern Kern Ozone SIP that This region is in close proximity to biogenic ROG emissions sources and farther away from the large anthropogenic NOX sources in the SJVAB and SCAB, such that low NOX
and high ROG conditions are prevalent, which is consistent with a NOX-limited regime. 36 While some of this evidence could be termed qualitative, the EPA
finds that it makes a compelling case that NOX emissions reductions are more effective than VOC reduction at decreasing ozone in Eastern Kern, and therefore that percentage-based NOX
substitution results in ozone reductions at least equivalent to those that would result from the VOC reductions required for RFP.
The 2017 Eastern Kern Ozone SIP
clearly documents that the Eastern Kern nonattainment area is strongly affected by transport of ozone from the SJV and SCAB.37 Although the EPAs proposed action did not discuss in detail the impact of transport on RFP, we are providing additional technical information to further clarify the relationship between transport from the SJV and SCAB and ozone formation in the Eastern Kern nonattainment area.
Photochemical modeling results in the 2016 Ozone Plan for 2008 8-Hour Ozone Standard for the San Joaquin Valley SJV 2016 Ozone Plan 38 and analyses of the San Joaquin Valley portion of the 2018 Updates to the California State Implementation Plan 2018 SIP Update 39 also support the conclusion that NOX reductions are doi.org/10.1080/1073161X.1993.10467187; cited in CARB Staff Report, p. A9.
33 Eastern Kern 2017 Ozone Plan, Appendix H, H21.
34 Eastern Kern 2017 Ozone Plan, Table 14, 37.
35 85 FR 68268, 6827568276.
36 Eastern Kern 2017 Ozone Plan, Appendix H, H22. As already noted, the 2017 Eastern Kern Ozone SIP primarily uses NOX-limited to mean NOX reduction are more effective than VOC
reductions. SJVAB is an acronym for the San Joaquin Valley Air Basin.
37 CARB Staff Report on the Eastern Kern 2017
Ozone Plan, A9, A13A18.
38 SJV 2016 Ozone Plan, San Joaquin Valley Unified Air Pollution Control District, June 16, 2016.
39 2018 SIP Update, CARB, October 25, 2018.

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more effective than VOC at reducing ozone in the Eastern Kern nonattainment area. The EPA approved a modeled attainment demonstration for the SJV 2016 Ozone Plan that used the same meteorological and photochemical models, model domains, and setup parameters, and covered the same 2012
ozone season as the Eastern Kern modeling.40 The SJV 2016 Ozone Plan contained an ozone isopleth diagram for the Clovis monitor,41 the SJV site with the highest ozone design value in 2031.
In support of the 2018 SIP Update, CARB provided supplemental documentation that used the isopleth diagram to show that the SJV attainment demonstration remained valid.42 As part of the EPAs approval of the SJV portion of the 2018 SIP Update,43 the EPA used the ozone isopleth diagram to estimate the sensitivity of ozone to VOC and NOX
emissions reductions.44 We determined that ozone changes by 0.313 ppb per percent change in NOX emissions, and by 0.0234 ppb per percent change in VOC emissions.45 On a percentage basis, NOX is 13.4 times as effective as VOC
at reducing ozone at the Clovis monitor.
The ozone response to emission changes is expected to be similar in western Kern County because both areas have similar meteorological conditions and a similar mix of emissions sources.
Eastern Kern is directly downwind of western Kern County. The mountain ranges to the northwest separate sparsely populated Eastern Kern from the more densely populated areas in the southern SJV, including western Kern County. However, the Tehachapi pass connects the SJV to Eastern Kern, facilitating the transport of emissions and pollutants into the region.46 For the reasons discussed earlier in this section, ozone formation in Eastern Kern is more NOX-limited than the larger urban areas of the southern SJV and western Kern County. Putting these together, ozone in Eastern Kern is expected to be 13 times or more as sensitive to NOX emissions 40 84

FR 3302 February 12, 2019.
2016 Ozone Plan, Appendix H, Figure 15, H54. Clovis is located in Fresno County, approximately 7 miles northeast of downtown Fresno.
42 Email dated October 19, 2018, from Sylvia Vanderspek, CARB to Anita Lee, EPA Region IX, with attachments.
43 83 FR 61346 November 29, 2018; See also the related final rule at 84 FR 11198 March 25, 2019.
44 Technical Support Document, Proposed Phase 2 Approval of Portions of the SJV 2016 Ozone Plan and 2018 SIP Updates, Docket: EPAR09OAR
20180535, EPA Region 9, November 14, 2018, including two attachments: Scale attainment demonstration with updated emissions and Effect of Updated Emissions Estimates on San Joaquin Valley Attainment Demonstration.
45 Id.
46 Eastern Kern 2017 Ozone Plan, H16.
41 SJV

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