Despite decreased road emissions across San Antonio during the early days of COVID-19, Bexar County still experienced more high-ozone days in the spring of 2020 than it did the previous year.

That is proof that pollution generated outside of the county is wafting in and negatively affecting San Antonio’s air quality, according to the local agency responsible for air quality monitoring.

And that’s why the San Antonio region shouldn’t be moved from “marginal” to “moderate” nonattainment for ground-level ozone by the U.S. Environmental Protection Agency, said Dianne Rath, AACOG’s executive director during a virtual hearing hosted by the federal agency Monday.

“There are a number of factors beyond local control,” Rath told regulators during the meeting, that “cause high levels of ozone” in San Antonio.

This data from early COVID-19 lockdowns, when vehicle traffic plummeted, “corroborates the modeling demonstrating most of our ozone comes from outside the area.” Because there were so few cars on the road during that time, the agency said it would have expected to see fewer high ozone days.

AACOG has long estimated that only 20% of San Antonio’s ground-level ozone is caused by local sources, whereas the other 80% comes from the rest of Texas, other states and even other countries, most notably Mexico.

Although nitrogen oxide emissions were down significantly during COVID-19 lockdowns due to reduced traffic, Bexar County still saw more high ozone days in the spring of 2020 than it did in 2019. AACOG argues this backs up their data that most of the area’s ozone-causing emissions are coming from outside of the county.
Although nitrogen oxide emissions were down significantly during COVID-19 lockdowns due to reduced traffic, Bexar County still saw more high ozone days in the spring of 2020 than it did in 2019. AACOG argues this backs up their data that most of the area’s ozone-causing emissions are coming from outside of the county. Credit: Courtesy / Alamo Area Council of Governors

Under the federal Clean Air Act, a city’s air quality must meet the ozone standard of 70 parts per billion (ppb) or less to safeguard the health of people with chronic lung conditions and prevent additional illnesses from developing. Ozone is a key ingredient of smog, which irritates and damages the lungs and has been tied to chronic conditions such as asthma. 

For many years, San Antonio was one of the few large cities that met national air quality standards, until those standards were tightened in 2015. The region was given until 2018 to lower its ground-level ozone to 70 ppb or below; that deadline was pushed back to 2020 at the state’s request.

San Antonio failed to meet the standard by the later cutoff date, prompting the EPAs action. If the federal agency does reclassify the region, the move could have serious economic impacts on the cost of growth and development, businesses and residents.

That’s why AACOG and others want the EPA to make allowances for outside pollution affecting the region; the latest data on high ozone days last spring, they say, backs up its previous data.

AACOG data shows double the number of high ozone days in April 2020 than in April 2019, from four to eight, AACOG spokesman Miguel Segura said.

“It’s clear that there are other forces outside our local control that are driving the county’s continued [nitrogen oxides] violations,” Rath said during the hearing Monday, “and we request that the EPA not reclassify Bexar County as moderate nonattainment at this time. Furthermore, AACOG urges the EPA to research the nationwide effects of COVID-19 on ozone precursors and on ozone itself.”

Lyle Hufstetler, natural resources project coordinator for AACOG, told the San Antonio Report that Texas Commission on Environmental Quality data also shows most of the area’s air pollutants are from outside sources.

Hufstetler said. “Ozone, like any air pollutant, is subject to winds, right? So we get a lot of pollution transported from other areas into our region,” Hufstetler said.

It’s unclear if the EPA will take this new data into account. In an emailed statement last week, EPA spokesman Joe Robledo told the San Antonio Report the EPA “did not find that any other state contributed significantly to the ozone levels in San Antonio,” and that “emissions from within the State of Texas are the most significant cause of high ozone in the San Antonio area.”

Regardless of the EPA’s decision, AACOG “will continue educating our regional stakeholders and state and federal partners about the studies we perform, the potential effects that ozone nonattainment has on public health, the environment, and our economies,” the agency stated in an email to the San Antonio Report.

The comment period for citizens and organizations to remark on the EPA’s proposed action closes on June 13.

Lindsey Carnett

Lindsey Carnett is the Science & Utilities reporter for the San Antonio Report.