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Vol. 50-2 Air Quality

February 11, 2021

By John Turney and Jacob Gildan

Air Quality

TCEQ Adopts Proposed Bexar County 2015 Eight-Hour Ozone Nonattainment Area FCAA, §179B Demonstration SIP Revision


On July 1, 2020, the Texas Commission on Environmental Quality (TCEQ) adopted the propose State Implementation Plan (SIP) Revision for Bexar County concerning the 2015 Eight-Hour National Ambient Air Quality Standard (NAAQS) for Ozone.[1] The SIP revision demonstrates, pursuant to Section 179B of the Federal Clean Air Act (FCAA), that the Bexar County marginal ozone nonattainment area would attain the 2015 standard “but for” anthropogenic emissions emanating from outside the United States.[2]  Given emissions and air flow trajectories, the proposal concludes sufficient ozone transport occurs from Mexico to prevent Bexar County’s from attaining the standard.[3]


Brief Overview of the Ozone Standards Under the FCAA

As authorized by the FCAA, the United States Environmental Protection Agency (EPA) issues NAAQS that individual states are required to meet by proposing and completing SIPs.[4] Previously, the EPA’s requirements for ozone levels were based on a one-hour standard, but this was phased out in favor of eight-hour standards.[5]

The 1997 eight-hour standard was 0.08 parts per million (ppm), or 80 parts per billion (ppb).[6] In 2008, the standard was lowered to 0.075 ppm (75 ppb) and in 2015, it was lowered again to 0.070 ppm (70 ppb), with anti-backsliding requirements for areas that did not qualify as attaining the standard.[7] Under the ozone standard, nonattainment areas can be designated as marginal, moderate, serious, severe, or extreme—depending on the extent of exceedance.[8]

Bexar County’s Status Under the 1997 EPA Eight-Hour Ozone NAAQS

The San Antonio area, along with twelve other Early Action Compact areas, reached attainment under the EPA’s 1997 Eight-Hour Ozone Standard in 2008.[9] Upon reaching this attainment, the one-hour ozone standard was revoked for the San Antonio area in April 2009.[10] As a result of being designated as attainment for the 1997 standard, the San Antonio area was no longer required to make any additional SIP revisions if the area continued to monitor attainment for the standard.[11]

Purpose of the Bexar County SIP Revision Proposal

Bexar County is currently working toward attainment under the 2015 Eight-Hour Ozone NAAQS and proposed a SIP revision to adjust its requirements for satisfying this standard.

On September 24, 2018, EPA designated Bexar County as marginal nonattainment (the least severe nonattainment level) under the 2015 NAAQS eight-hour ozone standard of 0.070 ppm, with a deadline of September 24, 2021 to achieve attainment.[12] Under EPA’s standards, attainment is measured based on three full years of monitoring data for marginal nonattainment areas, so Bexar County will need to meet the NAAQS standard based on its monitor data in 2018, 2019, and 2020.[13]

For nonattainment areas that might be influenced by emissions sources outside of the United States, states are allowed to submit to the EPA an analysis of the influence of international emissions on the nonattainment areas under FCAA §179B, and seek relief from some of the NAAQS requirements.[14] If a nonattainment area can show that it is affected by emissions from outside of the United States, EPA has discretion to approve a plan that demonstrates that the area will achieve NAAQS standard attainment by the required date, without including these international emissions in the calculation.[15] This is very beneficial for a nonattainment area because if the EPA approves such a revision, the area would no longer be required to meet certain benchmarks that normally apply, such as mandatory reclassification provisions for failing to reach the NAAQS standard by the deadline.[16]

Bexar County’s SIP Revision

The Bexar County’s 2015 eight-hour ozone nonattainment area is seeking this EPA approval under FCAA §179b to prevent being reclassified from marginal to moderate nonattainment if the area were not to meet the NAAQS standard during the 2018-2020 monitoring period.[17] With EPA approval, the area would still be designated as marginal nonattainment until it ultimately meets the 2015 standard, even if it doesn’t meet the requirements during the 2018-2020 monitoring period.[18]

 To determine the extent of international emissions on Bexar County’s 2015 eight-hour ozone nonattainment area, TCEQ conducted an analysis that examined several factors.[19] The analysis looked at the nonattainment area’s modeled 2020 future-year design value (DVF), the estimated international anthropogenic contribution, the effect of local versus boundary conditions, and the area’s current monitored design value.[20] The analysis included sophisticated photochemical modeling utilizing meteorological and detailed emission inputs to simulate the formation and transport of ozone.[21] TCEQ determined that while most of the air flow trajectories across Mexico correspond to monitored ozone concentrations under the 70 ppb standard, a sufficient number of those trajectories corresponded to concentrations above 70 ppb, to compromise Bexar County’s status.[22]  Accordingly, the analysis concludes that the Bexar County nonattainment area would achieve the NAAQS standard by the end of the 2018-2020 monitoring period, “but for” international anthropogenic contributions.[23]

A complicating factor affecting the proposal is that the EPA has not yet published guidance regarding FCAA §179B transport demonstrations, though such guidance is under development.   The proposal notes this lack of guidance and commits to appropriate amendments when it is issued.[24]

Bexar County officials supported the TCEQ analysis and requested its submittal to the EPA as sufficient under the requirements of FCAA §179B, as discussed above.[25] On January 15, 2020, the TCEQ approved this request.[26] Following TCEQ approval, the proposed SIP revision was subject to a public comment period from January 17 through February 19, 2020. There was a public hearing scheduled for February 18, 2020. TCEQ adopted the SIP revision on July 1, 2020.[27]

John Turney is retired Senior Counsel of Richards Rodriguez & Skeith and represented regulated companies in a variety of environmental and administrative matters before the TCEQ and other regulatory agencies. He is a graduate of Texas A&M University and The University of Texas School of Law.

Jacob Gildan is a third-year student at The University of Texas School of Law and a senior editor for the Texas Environmental Law Journal.


[1]               San Antonio: Latest Ozone Planning Activities, Tex. Comm’n on Envtl. Quality (Aug. 11, 2020), https:/ /

[2]               Id.

[3]               See Tex. Comm’n on Envtl. Quality, Agenda Item Request for Proposed Revision of the State Implementation Plan 1 (Jan. 15, 2020).

[4]               Evan Z. Pearson & John B. Turney, TCEQ Redesignation Request and Maintenance Plan for the HGB Area’s One-Hour and 1997 Eight-Hour Ozone National Ambient Air Quality Standards, 49 Tex. Envtl. L.J. 339 (2019).

[5]               Id.

[6]               Id.

[7]               Id.

[8]               Id.

[9]               San Antonio: Latest Ozone Planning Activities, Tex. Comm’n on Envtl. Quality (Aug. 11, 2020),

[10]             Id.

[11]             Id.

[12]             Tex. Comm’n on Envtl. Quality, Agenda Item Request for Proposed Revision to the State Implementation Plan at 1 (Jan. 15, 2020).

[13]             Id.

[14]             Id.

[15]             Id.

[16]             Id.

[17]             Id.

[18]             Id.

[19]             Id. at 2.

[20]             Id.

[21]             Revisions to the State of Texas Air Quality Implementation Plan for the Control of Ozone Air Pollution at 2-3, supra note 3. 

[22]             Id. at 2–41.

[23]             Tex. Comm’n on Envtl. Quality, Agenda Item Request for Proposed Revision to the State Implementation Plan at 2 (Jan. 15, 2020).

[24]             Id. at 3.

[25]             Id. at 2.

[26]             Id.

[27]             San Antonio: Latest Ozone Planning Activities, Tex. Comm’n on Envtl. Quality (Aug. 11, 2020),