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Federal Register / Vol. 86, No. 156 / Tuesday, August 17, 2021 / Rules and Regulations
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detail in EPAs April 2021 SNPRM and summarized in this final rule. EPA also notes that in the April 2021 SNPRM, the Agency explains that with regard to the I/M program, NO2 is captured generally through consideration of NOX impacts.
B. Responses to Comments Related to the Non-Interference Demonstration EPA received technical comments asserting that the non-interference demonstration is inadequate to approve the SIP revisions. EPAs evaluation of these comments and responses is provided below.
Comment B1: In response to EPAs June 2020 NPRMs, a commenter asserts that the non-interference demonstrations cannot be considered technically complete without air quality modeling to simulate the impact of removing the I/M program. The commenter recommends a full air quality simulation of the impact of removing the I/M program specifically suggesting the use of a transport grid modelto ensure that increases in air pollutant concentrations do not exceed NAAQS and health-based recommendations. The commenter also recommends that the air quality simulation utilize the most current modeling platform and associated emission projections, as well as meteorological and base year inventories that meet EPA guidance.
The commenter cites EPA SIP modeling guidance in support of its recommendations. To further support its modeling recommendation, the commenter expresses concerns regarding the use of historical trends in air quality and emissions to evaluate impacts of I/M program removal due to annual variations in meteorology and actual emissions and the need for a solid conceptual model of how ozone or PM2.5 is formed in the areas. Also, in response to EPAs April 2021 SNPRM, the commenter reasserts its position that the non-interference demonstration should be based on air quality modeling, asserting that a case-by-case determination by EPA that air quality modeling is warranted with respect to the removal of the I/M program; the commenter further provides a number of comments related to the ozone sensitivity analysis that Tennessee provided in its SIP revisions. The commenter does not provide substantive comments on EPAs technical noninterference demonstration as provided in the April 2021 SNPRM.
Response B1: EPA does not agree with the commenter that air quality modeling is required in order for EPA or the State to assess, pursuant to section 110l of the CAA, whether removal of the I/M

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program from Tennessees SIP will interfere with attainment or maintenance of the NAAQS or any other requirement of the CAA. EPA
acknowledges that air quality modeling is an option that could be used to evaluate the impact of removal of the I/M program. However, other technical analyses that do not involve modeling may also be used for section 110l demonstrations.
EPA refers the commenter to EPAs April 2021 SNPRM for more detail related to EPAs non-interference analysis. Also, as further explained in EPAs June 2020 NPRMs and April 2021
SNPRM, the pollution control systems for light-duty gasoline vehicles subject to the I/M program are not designed to reduce and do not reduce emissions for PM, lead, and SO2 in Tennessee.
For CO and ozone, EPA reviewed Tennessees MOVES2014b mobile modeling which estimated emissions in 2022 with and without the I/M
program.21 Tennessee developed an inventory based on the best available information to the State at the time of the submissions for both Hamilton County and the Middle Tennessee Area.
EPA reviewed the inventory with and without the benefit of the I/M program for each area. As EPA noted in the June 2020 NPRMs and the April 2021
SNPRM, there was a slight increase in NOX and VOC on-road emissions for each area for 2022 for the scenarios without the I/M program, as compared to the scenarios with the I/M program.
For ozone, EPA agrees with a commenters statement that ozone formation in Tennessee is NOX-limited i.e., ozone concentrations are most effectively reduced by lowering NOX
emissions rather than VOC emissions.22
Nonetheless, as discussed in the April 2021 SNPRM, EPA evaluated both the increases in on-road VOC and NOX to determine whether the increase in total emissions in 2022 would interfere with attainment or maintenance of the ozone NAAQS in either area. EPAs analysis 21 Tennessee chose 2022 as the future year for the States non-interference demonstrations because it is the year when the State anticipated that the Areas will cease implementation of the I/M program due to the CAAs SIP processing timeframe and the language of Tenn. Code Ann. section 68201119.
22 As part of the Southeastern Modeling and Analysis Planning SEMAP project, Georgia Institute of Technology performed an analysis of the sensitivity of ozone concentrations in the Eastern U.S. to reductions in emissions of both NOX and VOC and determined that the Southeast is NOX
limited. This analysis was based off the 2007 and 2018 SEMAP modeling which used the Community Multi-scale Air Quality model, version 5.01 with updates to the vertical mixing coefficients and landwater interface. May 1st through September 30th was modeled using a 12-km modeling grid that covered the Eastern U.S.

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presented in the April 2021 SNPRM
demonstrates that total emissions in these areas are projected to decrease significantly from the 2014 base year to the 2022 future year, even if the I/M
program is discontinued. The small increase in on-road emissions resulting from removal of the I/M program in 2022 are overcome by the continued decrease in total emissions, despite increases in vehicle miles travelled, due to fleet turnover i.e., old vehicles being replaced with new vehicles that meet more stringent engine standards.
EPA disagrees with the commenters concerns regarding the use of historical trends in air quality and emissions to evaluate impacts of I/M program removal due to annual variations in meteorology and actual emissions and the need for a solid conceptual model of how ozone or PM2.5 is formed in the areas. EPA acknowledges the importance of understanding the factors affecting ozone and PM2.5 formation in an area, and Response A6 provides information about factors affecting ozone and PM2.5 in Tennessee. Concerns about annual variations in meteorology are addressed in Response A3. EPA
believes that the large decreases in emissions of NOX, VOC, and CO
described in the April 2021 SNPRM
overshadow the effects of annual variations in actual emissions.
Although Tennessee included photochemical modeling sensitivity analyses to provide additional weight of evidence in its submissions, as described by EPA above and in the April 2021 SNPRM, such analyses were not required and were not the basis for EPAs proposed determinations that removal of the I/M program from Hamilton County and the Middle Tennessee Area would not interfere with attainment or maintenance of the NAAQS or any other applicable CAA
requirements. Specifically, in the April 2021 SNPRM, EPA clarified that it was not the Agencys intention to rely on Tennessees ozone sensitivity analysis.
Thus, any comments related to the sufficiency of that ozone sensitivity analysis are not relevant to the actions that EPA are finalizing in this document. EPAs conclusion that these removals satisfy CAA section 110l is based on the technical analysis presented in EPAs April 2021 SNPRM.
Comment B2: With respect to the commenters concerns on the June 2020
NPRMs and the April 2021 SNPRM
regarding the nonlinearity of ozone formation related to Tennessees sensitivity analysis, the commenter
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