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Federal Register / Vol. 86, No. 120 / Friday, June 25, 2021 / Rules and Regulations isopleth diagrams together with conservative assumptions about the amount of allowable NOX substitution.
Response to Comment 3: First, we disagree that the plural concentrations in CAA section 182c2C necessarily means that equivalence must be demonstrated throughout the nonattainment area.
However, in this instance, it does not matter because all locations within the Eastern Kern nonattainment area are downwind of, and more NOX-limited than, the SJV and the SCAB, for which NOX reductions are more effective than VOC. Therefore, NOX reductions are more effective than VOC for all locations in the Eastern Kern nonattainment area.
Second, we disagree that equivalence demonstrations necessarily must be quantitative estimates. Analytical information that establishes equivalence may be quantitative or qualitative, or both, depending on the facts and circumstances of any given area. In this instance, as discussed above, some of the evidence relied upon could be termed qualitative, such as the known tendency for ozone formation to become more NOX-limited with distance downwind of an urban area, and the relative sizes of emissions inventories for Eastern Kern and the upwind areas.
This relatively qualitative evidence was coupled with more quantitative assessments of the degree of NOXlimitation weekday-weekend differences. Qualitative evidence can be just as useful as quantitative evidence.
For NOX substitution to yield an equivalent ozone decrease as required in section 182c2C, we only need to know that reductions of NOX are at least as effective as reductions of VOC for reducing ozone concentrations. Further, the estimate that NOX emissions reductions are 13 times as effective as VOC reductions is quantitative, not qualitative.
With respect to post-2015 emissions changes, we note that NOX and VOC
emissions in Eastern Kern are projected to decrease slightly after 2015 through year 2021, largely due to reductions in mobile source emissions offsetting increases from stationary and area sources.52 In the upwind areas of SJV
and SCAB, the same is true but NOX
emissions are projected to decrease at a faster rate than VOC emissions,53 which would have the effect of increasing the VOC:NOX ratio, making Eastern Kern even more NOX-limited. The emissions projections in the 2017 Eastern Kern 52 Eastern 53 CARB

Kern 2017 Ozone Plan, Appendix A.
Staff Report on Eastern Kern 2017 Ozone
Plan, A8.

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Ozone SIP take into account long-term trends for the various source categories, including electricity generation. The commenter has not cited any particular natural-gas power plant closure that would affect the Eastern Kern area, and we are not aware of any such closure.
The possible replacement of NOXproducing electricity generation by wind and solar power cited by the commenter would also tend to make the area more NOX-limited. The geographic distribution of the emissions changes is also not of concern. Emissions from the upwind areas are channeled through a small set of mountain passes regardless of their precise upwind location.
Emissions within Eastern Kern itself are so much lower than those of the upwind areas that their particular location within the nonattainment area does not affect the NOX-limited conditions there.
Because the VOC:NOX ratio of emissions input to the model increases between 2012 and 2020, if additional modeling were carried out using 2020 emissions, it is expected that ozone formation would be even more NOX-limited.54
Thus neither the magnitude nor the geographic distribution for the post2015 emissions would change the EPAs conclusion that the NOX substitution used for the RFP demonstration in the 2017 Eastern Kern Ozone SIP meets the requirements of CAA section 182c2C.
Lastly, we note that CAA section 182c2C, in contrast to CAA section 182c2A, does not explicitly prescribe the use of photochemical grid modeling or equivalent analytical method to demonstrate the equivalence of NOx emission reductions relative to VOC emissions reductions on ozone concentrations. The NOX equivalence demonstration for RFP purposes need not be based on the same analytical methods used in the attainment demonstration. Therefore, we are approving the RFP demonstration and its reliance on NOX substitution for a portion of the VOC emissions reductions otherwise required based on both qualitative and quantitative technical analyses.
54 This is an approximation based on SJV NO
X and VOC emissions in tons per day as shown in the bar chart in CARB Staff Report on the Eastern Kern 2017 Ozone Plan see A8; SJV is the area most often upwind of Eastern Kern, and its photochemical modeling includes both areas. The VOC:NOX ratios increase because NOX declines more than VOC. Specifically the VOC:NOX ratios for 2010, 2015, and 2020, respectively are 380/400
= 0.95, 315/267 = 1.18, and 300/205 = 1.46, an increasing sequence that spans the 20122020
period. Another estimate can be made using the SJV
emissions from the 2016 SJV Ozone Plan. The summer tons per day VOC:NOX emissions ratio increases from 337.3/339.6 = 0.99 in 2012 to 300.2/
212.7 = 1.41 in 2020.

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Comment 4: CBD asserts that the EPA fails to give notice of how the submittal addresses the demonstration required under CAA section 182c2C
and thus the EPAs proposal is not in accordance with procedure required by law. In particular, the commenter states that EPA has failed to give adequate notice of its proposed interpretation of section 182c2C. The commenter observes that Table 3 of the proposed rule treats a percentage of NOX
reductions as equivalent to an equal percentage of VOC reductions, but asserts that the proposed rule does not explain why a percentage reduction in NOX emissions results in equivalent ozone reductions to an equal reduction in VOC emissions, as required by section 182c2C. The commenter suggests that the proposed rule may have used the procedure recommended in a December 1993 guidance document from the EPAs Office of Air Quality Planning and Standards entitled NOX
Substitution Guidance. The commenter argues that because the NOX
Substitution Guidance is non-binding, the notice must indicate whether the EPA intends to adopt the Guidances interpretation of the CAA, and that if the EPA instead believes that the Eastern Kern calculation is a legitimate demonstration for other reasons, it must re-propose the action.
Response to Comment 4: The EPA
disagrees with the commenter that the proposed rulemaking fails to give adequate notice regarding our proposed approval of the Districts use of NOX
substitution, or that we would be required to re-propose with additional justification prior to taking final action on this portion of the proposal. As described in responses to comments 2
and 3 above, the modeling and analysis submitted to support the Districts control strategy and attainment demonstration highlight the need for significant NOX reductions in the upwind San Joaquin Valley and South Coast Air Basin for the Eastern Kern to attain the 2008 ozone NAAQS, and demonstrate that these NOX reductions will be more effective on a percentage basis than VOC reductions at reducing ozone concentrations in the nonattainment area. As described below, our proposal includes a summary and analysis of relevant portions of the SIP submittals, including NOX substitution in the RFP
demonstration.
Section III.C of the proposed rulemaking describes our proposed approval of the Districts RFP

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