East Tennesseans can breathe a little easier - at least for now.
Seven years of work finally paid off Thursday when federal regulators declared Knox County's air to be in compliance with national ozone standards.
The U.S. Environmental Protection Agency gave Knox and six other East Tennessee counties, along with the Great Smoky Mountains National Park, a failing air-quality grade in 2004, saying ozone, a primary component in smog, in those areas often reached unhealthy levels. The region has made "significant progress" since then, according to the EPA.
"Now it's just a matter of staying in attainment," EPA spokeswoman Dawn Harris-Young said. "As far as we understand, the city and county intend to keep it that way."
That compliance might not last long. The EPA plans to publish revised ozone standards this summer, based on updated health studies and other scientific data, that could push the area back into violation. Knox County still remains above the air-quality standard for particulate matter.
"It's good news, but we have to be cautious," Knox County Mayor Tim Burchett said. "We need to be prepared for another fight, or this victory could be short-lived."
Achieving compliance required the county to present the EPA with three years' worth of air-quality measurements that showed improvement.
Knox and the other counties - Anderson, Blount, Jefferson, Loudon, Sevier and part of Cocke - worked together with the state Department of Environment and Conservation to reach the current standard, set in 1997. The process included lowering interstate speed limits and banning some burning in Knox County.
"We tried to get people focused on ideas of things they could do," said Lynne Liddington, Knox County director of air-quality management. "TVA did a lot to reduce emissions by putting scrubbers on most of their coal-fired power plants."
Knox County's ozone level last year averaged around 77 parts per million, Liddington said. She expects the new EPA standard to be somewhere between 60-70 parts per million.
"Looking at our numbers, we would not meet it," she said. "The biggest problem right now is motor vehicle traffic. That's not something we're going to be able to affect much at the county level. We can't stop vehicles at the county borders."
Liddington said she expects some improvement on that front as automakers continue to produce cleaner, more efficient cars.
Some environmental groups believe it might take more than that.
"We think this is important work, and we think it's necessary," said Stephen Smith, executive director of the Southern Alliance for Clean Energy, an environmental advocacy group. "All this helps to improve health and lower costs in the long run."