San Antonio’s air is indeed too polluted to meet federal health standards, a Fifth Circuit Court of Appeals panel ruled Wednesday in a decision backing the U.S. Environmental Protection Agency.

In July 2018, the EPA declared levels of ozone in San Antonio’s air quality as too high to meet standards under the federal Clean Air Act. The State of Texas appealed the EPA’s decision to the Fifth Circuit in October of that year, seeking to avoid new air quality regulations.

Citing public health concerns, environmental groups later intervened in the case. The Sierra Club, one of the largest such groups in the U.S., said the EPA didn’t go far enough and wanted to expand the pollution designation to three surrounding counties.

Neither Texas officials nor Sierra Club members got what they wanted, with a panel made up of U.S. Circuit judges Edith Brown Clement, Jennifer Walker Elrod, and Stuart Kyle Duncan issuing a ruling Wednesday that upheld the EPA’s designation.

In the ruling, the judges wrote that the “EPA, not the State, has the primary responsibility” for deciding whether localities meet health standards under the federal Clean Air Act. States are primarily responsible for planning how to improve air quality enough to meet the standards, the ruling states.

A spokesperson for the Texas Attorney General’s office didn’t immediately respond to emailed questions Wednesday.

Peter Zalzal is senior counsel for the Environmental Defense Fund (EDF), which intervened in the case to support the EPA’s Bexar County decision. Zalzal was also involved in a 2017 case in California federal court that prodded the agency to act on San Antonio’s ozone levels in 2018.

“It’s been a long time in the works,” Zalzal said. “We’re glad to see guarantees reflected in the Clean Air Act have been affirmed.”

Ozone – three oxygen atoms bound together – is a key ingredient of smog. It irritates and damages the lungs and has been tied to chronic conditions such as asthma. Air quality is one of several factors contributing to San Antonio’s high child asthma rates.

In San Antonio, high ozone season generally lasts from March through November. That’s when conditions are perfect for nitrogen oxides from power plants, industrial sites, and vehicle tailpipes to interact with volatile organic compounds from outdoor chemical use and other sources in the presence of heat and sunlight.

Since the EPA’s designation in 2018, the State has sought to overturn the decision. Officials from Texas Gov. Greg Abbott’s office and the Texas Commission on Environmental Quality have argued that San Antonio would meet standards if not for air pollution wafting in from foreign countries.

In their legal fight with the EPA, Texas officials also pointed to computer modeling they said showed that San Antonio’s air quality would improve enough without new regulations to meet the ozone standard by 2020.

The Fifth Circuit panel concluded that the State’s argument was “based not on fact but on supposition.”

“Even with the best available modeling data, Texas could not be certain of future events and future attainment,” the ruling states.

The State’s modeling didn’t prove correct. Even with coronavirus lockdowns in March and April that cut vehicle traffic and cleared skies over major Texas cities, San Antonio’s current three-year regulatory ozone level remains at 72 parts per billion, slightly above the 70 parts per billion standard.

But over the long term, San Antonio’s ozone levels have been dropping. From 2015 to 2017, the period of record for the EPA’s decision, San Antonio’s ozone averaged 74 parts per billion. The recent high was 90 parts per billion in 2004, with the reduction in ozone levels since then mostly attributed to better vehicle emissions standards.

San Antonio would have met an earlier 75-parts-per-billion ozone standard set in 2008, but the Obama-era EPA ratcheted it down to 70 parts per billion in response to public health concerns. On Wednesday, the EPA declined to strengthen the standard further, despite pressure from public health advocates.

In its legal filings, the Sierra Club said that the EPA should also have designated Atascosa, Comal, and Guadalupe counties as out of line with the ozone standard, arguing that pollution in those counties contributed to poor air quality in Bexar County.

In this matter, Fifth Circuit judges also deferred to the EPA, saying the agency had “determined that the prevailing winds were more likely to carry particles from Bexar County to two of the three contested counties, not the other way around.”

Brendan Gibbons is a former senior reporter at the San Antonio Report. He is an environmental journalist for Oil & Gas Watch.