After decades of trying to clean up its dirty air image, Chattanooga finally is meeting what proved to be the toughest of its challenges to completely comply with federal clean air standards.
The U.S. Environmental Protection Agency announced Tuesday that Chattanooga now meets two - not just one - federal smog standards.
The city now is in compliance with regulations that limit fine-particulate emissions - fine particles of dust, soot or smoke that contain microscopic solids or liquid droplets so small they can get deep into the lungs and cause serious health problems.
Since 2008, Chattanooga has been in compliance with ground-level ozone requirements. Ground-level ozone comes primarily from vehicle and power plant emissions.
Both particle pollution and ground ozone contribute to smog.
Chattanooga's breakthroughs - met with burning bans, emissions testing and power plant pollution reductions - mean that new and recruited industries soon will not have to depend on offset pollution emissions from other businesses to get local air permits.
"The private and corporate citizens of Hamilton County again have shown that they can meet any challenge," said Bob Colby, director of the Chattanooga-Hamilton County Air Pollution Control Bureau.
Might the breakthroughs also mean less need for emissions testing and burning bans? Not likely, Colby said.
"With tighter standards always coming down the pike [from EPA], I don't think that is likely. Certainly not in the near future," he said.
EPA's Richard Schutt, chief of the air planning branch for the Southeast Region, said the final requirement for Chattanooga to be taken off what is known as the "nonattainment list" maintained by the EPA is for federal regulators and officials in the city's tri-state region to negotiate a 10-year plan to maintain the successful clean air effort.
That could take several months, he said, but the official notice that Chattanooga now complies with the three-year average on fine particulates was published in Tuesday's Federal Registrar.
EPA announced similar attainment of its smog standards for Knoxville in March and for Rome, Ga., in April.
"It's really what we're seeing as the trend in the Southeast," Schutt said. "Chattanooga is just another area we've seen bring improvements to air quality."
Chattanoogans, still smarting from the 1969 EPA designation as the "dirtiest air" city in the country, see the accomplishment as monumental.
After instituting auto emissions controls and open burning bans in 2005, the Chattanooga region squeaked by to obtain a "pending" tag of ozone compliance for the three-year period ending in 2007. Had monitors logged two additional bad ozone air days during that period, the city wouldn't have made it, Colby said at the time.
A year later, the city officially was declared "in attainment" for ozone, but not before arguing to EPA that raging Florida wildfires created some of the unhealthy air days here.
But fine particulate pollution proved a tougher challenge.
To meet EPA's fine particles limit of 15 micrograms per cubic meter of air, Chattanooga had to drop its three-year annual average from 17.5 to 11.7 micrograms, Colby said.
Now EPA is contemplating dropping the standard "to between 11 and 13," he said.
Schutt said the intent is to continue getting the air cleaner and cleaner.
"Some of these particles - there's not really a bright line [for where to set the standard]," he said. "As we get better informed, we know we need to do more. So the job's not done yet."
Staff writer Dave Flessner contributed to this story.