With a deadline approaching for the U.S. Environmental Protection Agency to say whether San Antonio’s air meets federal health standards, a Trump administration memo indicates the agency will consider “pollution from foreign sources” in making its decision.

In a recent memo, President Donald Trump directed EPA Administrator Scott Pruitt to work more closely with the states “in identifying potential exceptional events and international emissions that may affect concentrations of” ozone and other pollutants.

Under a court-imposed deadline, the EPA must say by July 17 whether Bexar County faces more strict regulation of its air quality for not meeting a 2015 federal health standard for ozone, a key component of smog.

The standard for ozone is 70 parts per billion. San Antonio’s value for ozone from 2014 to 2016, the period of record for the EPA’s decision, was 73 parts per billion.

San Antonio is the only major city in the U.S. not under such regulations and will be the last city in the U.S. to find out its status under the 2015 standard. In Texas, the EPA has already said the Dallas-Fort Worth and Houston metro areas’ air doesn’t meet the standard.

The language about foreign emissions in the Trump administration’s April 18 memo closely mirrors arguments by Texas Gov. Greg Abbott and local officials, especially those of Diane Rath, director of the Alamo Area Council of Governments (AACOG).

At a June 21 hearing of a U.S. House subcommittee on the environment, Rath said that San Antonio’s air would meet the health standard if it weren’t for pollution blowing in from other countries.

“We urge the EPA to take advantage of the flexibility in the Clean Air Act to evaluate and actively consider … the impact of background ozone levels and all foreign transport on a region,” she said.

At the hearing, Rath cited ozone modeling efforts by AACOG staff that state that on high ozone days, only 21 percent of San Antonio’s ozone comes from the metro area, the rest coming from other parts of Texas, northern Mexico, Canada, and more far-flung regions.

That differs from modeling efforts by EPA staff. In a March technical document, released before the Trump administration memo, the EPA blamed most of Bexar County’s ozone pollution on vehicle traffic and pollution sources like power plants and cement kilns within county lines.

“It’s not at all uncommon to see battles of these models,” said Thomas McGarity, a University of Texas School of Law endowed chair in administrative law who has served as an advisor to the EPA and other federal agencies.

“To some extent, policy winds up creeping into those models, to be perfectly honest with you,” he said. “It all comes down to, of course, the assumptions that are built into the models, and that can get highly technical.”

With rare exceptions, courts have found in favor of the EPA’s modeling, McGarity said.

But it’s not yet clear whether the EPA will rely on the same modeling it conducted before the Trump administration’s April memo. Before his appointment to head of the EPA, Pruitt as Oklahoma’s attorney general fought with the agency over multiple environmental issues. That included joining Texas in a lawsuit challenging the 2015 ozone standard.

“EPA may change its model, now that it has a new administrator,” McGarity said. “He is ordering them to do all sorts of things with respect to cost-benefit analysis and modeling. … I think that’s to make it so that they don’t regulate as much.”

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Brendan Gibbons

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