The Environmental Protection Agency did not include the San Antonio metro area in its list of places that meet federal health standards for ozone, a sign that the agency is considering pollution that wafts in from other places.

Bexar County and its neighbors — Atascosa, Bandera, Comal, Guadalupe, Kendall, Medina and Wilson counties — were not among the 2,646 counties designated as meeting the air quality standard in a rule the EPA issued this month.

“I think it’s very encouraging because I think it does indicate that EPA is taking time and really studying the data and the circumstances that we have that particularly make us unique,” said Diane Rath, director of the Alamo Area Council of Governments, a coalition of county and municipal governments whose staff studies ozone in the region.

Those 2,000-plus counties said to be in compliance “are sort of the easy ones,” she said.

“When you look at those counties that have not been designated, they’re really surrounding cities that have been borderline or in noncompliance in the past.”

Ground-level ozone — three oxygen atoms bound together — is a key component of smog that irritates and damages the lungs. It forms when emissions from power plants, industrial sites, engine exhaust and outdoor chemical use react in sunlight.

About a third of San Antonio’s ozone-forming pollution blows in from outside the U.S., from Mexico and South America, said Rath, citing AACOG computer modeling of ozone sources.

Another third comes from other parts of the U.S., and the remainder comes from the San Antonio area.

Some say San Antonio should not be overly focused on ozone coming from elsewhere and should continue to cut emissions here.

“Locally, we know the air quality is an issue for children, seniors, those with respiratory disease, what we call our most vulnerable,” said District 7 Councilwoman Ana Sandoval, who once worked for a local air quality regulator in California, at an October air quality forum.

Bexar County’s long-term ozone levels stand at 73 parts per billion, slightly above a standard of 70 ppb set in 2015. Ozone levels here have declined from a high of 91 ppb in 2004, according to AACOG reports.

If ozone levels drop below 68 ppb, 24 deaths per year in Bexar County could be avoided, according to a health study released in full by the city of San Antonio on Wednesday.

If concentrations return to 2012 levels of 80 ppb, Bexar County would see 19 additional deaths per year from lung conditions, the study by Ranboll Environ states.

In Texas, 49 counties with a decision still pending are clustered around Houston, Dallas, San Antonio and El Paso. EPA officials say they are “not yet prepared” to make a decision on those cities, according to a news release.

“In the spirit of cooperative federalism, EPA will continue to work with states and the public to help areas with underlying technical issues, disputed designations and/or insufficient information,” it states.

Specifically, the EPA is considering “international emissions and background ozone,” two factors that make a difference in the San Antonio’s air quality.

The phrase “cooperative federalism” comes directly from EPA Administrator Scott Pruitt, who in an October memo wrote that “EPA can work cooperatively with states to encourage regulations instead of compelling them.”

As Oklahoma attorney general, Pruitt repeatedly sued the federal government over Obama-era environmental regulations.

EPA officials did not immediately respond to requests for comment.

A recent AACOG modeling study states that San Antonio’s ozone levels will likely decline to 68 ppb by 2023 because of CPS Energy reducing coal plant emissions and improvements in vehicle efficiency.

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