The battle between Texas pollution regulators and the Environmental Protection Agency grows more contentious and complex by the day. Gov. Rick Perry accused the EPA on Wednesday of "seek[ing] to destroy Texas’s successful clean air program and threaten tens of thousands of good Texas jobs in the process." Environmentalists fired back, in their own news conference, threatening to sue the EPA if the agency doesn't make the state shape up.

The back-and-forth follows the EPA's announcement last week that it will strip the state of permitting authority for a huge refinery in East Corpus Christi. The Texas Commission on Environmental Quality, the EPA said, was doing a shoddy job — and the agency threatened to take more plants away from TCEQ jurisdiction unless it changes its permitting system.

So does all the hubbub mean that Texas' air is dangerous to breathe? Mostly no. But exactly how safe it is and exactly who gets the credit are open questions.

In general, even the EPA acknowledges, the air above Texas cities is getting better. "Progress has been made over the years," says Dave Bary, a spokesman for the EPA's Region 6, the five-state area that includes Texas. Only Dallas-Fort Worth, Houston-Galveston and Beaumont-Port Arthur are "non-attainment" areas for ozone, which means that they do not meet federal standards developed under the Clean Air Act. The EPA forces improvements in city air quality by threatening to withhold federal transportation money, but it has never carried out this threat.

The governor's office trumpets the improvements. "The air Texans breathe today is significantly cleaner than it was in 2000," it said in a news release Wednesday. Between 2000 and 2008, the release said, Texans have cut ozone by 22 percent and nitrogen oxide by 27 percent — more than the national average.

Things aren't quite so simple, environmentalists say. First, they argue, credit for improvement belongs to the EPA, not Texas. "It was the feds who came in and said, we're going to cut off transportation funding" unless things improve, says Tom "Smitty" Smith, the state director of the environmental and consumer advocacy group Public Citizen. Federal requirements for cleaner cars and trucks have also been crucial.

Second, environmentalists say that the EPA could still be doing more to force improvements in Texas. On Wednesday, the Sierra Club and Earthjustice sent out a notice of intent to sue the EPA unless it enforced ozone standards in Texas more strictly. Enforcement has been slowed, they said, by foot-dragging by the Perry governor's office — as well as lax regulation during the eight years that George W. Bush was in the White House. The EPA plans to issue new ozone standards by the end of August, and when it does, more areas of the state — including Austin, San Antonio and northeast Texas — will be designated "non-attainment," according to Neil Carman, the clean air program director for the Sierra Club's Texas chapter.

Los Angeles, another badly polluted city, has improved faster than Texas cities, says Smith of Public Citizen. In addition, according to Bary of the EPA, only one non-Texas city in his five-state region currently fails to meet EPA standards: Baton Rouge.

In addition to broad battles over urban air, environmentalists say problems persist with localized pollution hotspots. Texas has the biggest industrial base in the country, and concerns center on the land and water near big plants such as refineries, chemical factories and cement kilns.

It is on these individual plants that the original battle — the one set off last week by the Corpus Christi refinery announcement — hinges. The TCEQ issues vast numbers of permits every year, and only 120 are flexible permits, the commission says. But the flexible permits are granted to some of the biggest plants, including the Corpus Christi refinery. Environmentalists say these "flexible" permitting arrangements for big plants are an outrage, and the EPA seems to agree.

So what are flexible permits? In essence, they put a cap on the overall emissions of a facility. The plant must meet the cap but can choose the most expeditious manner. Texas has had flexible permitting in place since the mid-1990s (environmentalists have been fighting the system ever since). The EPA's permitting procedures are more precise, specifying limits for the units within each facility.

The flexible permits create three problems, says Ilan Levin, the Texas program director for the Environmental Integrity Project, a nonprofit that advocates for better enforcement of environmental laws. First, TCEQ sets the overall emissions cap too high — allowing higher total pollution levels than what EPA-recommended caps on individual units within the facility would permit. "Those caps don't really do anything; they don't mean anything," Levin says. Second, they may result in pollutants that are too concentrated in one area of the plant — harming a school, waterway or neighborhood nearby. Third, the flexible permitting scheme means that emissions from units within the plant are not monitored and reported properly.

"There's no other state out there that has anything like Texas's flexible permit program," Levin says. "These flex permits do nothing. They're worthless."

The TCEQ, not surprisingly, "strongly disagrees that Texas air permits violate the Clean Air Act," as the agency's chairman, Bryan Shaw, said in a statement last week. Shaw also said that the environmentalists' criticism of the flexible permitting scheme are "all incorrect." To ensure no particular unit of the plant has dangerous emissions, the TCEQ does “worst-case modeling," he said. And plants must also provide emissions reports from individual units within the plant "upon request."

More broadly, Perry and industry representatives fiercely argue that revoking the flexible permitting scheme will harm the big plants by depriving them of, well, flexibility. In other words, the more rigid permitting scheme would be cumbersome and expensive. The EPA is far too obsessed with process and not enough with results, TCEQ says.

Bary emphasizes that the Corpus Christi refinery issue — and the possibility of the EPA taking over permitting for more plants — should be considered separately from the larger ozone issues facing Texas cities. Carman, for his part, offers an analogy: Decades ago, cars spewed filth into the atmosphere; now they are fairly clean. Why can't industrial plants — some of them built decades ago — also clean up at a similar rate?

"I have been waiting for 15 years for this to hit the fan," Carman says. "It's a huge mess."