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KNOXVILLE, Tenn.–Coal and cars are the major reasons Tennessee has some of the nation’s unhealthiest air, a University of Tennessee civil and environmental engineer said Friday.

“Some areas use more natural gas or nuclear power to generate power, but in Tennessee we burn more coal,” Dr. Wayne Davis said. “Burning coal releases nitrous oxides — a key factor in forming smog. That is why we have more of a smog problem than other states.”

The U.S. Public Interest Research Group reported that Tennessee had 74 days in 1999 when air quality violated the federal standard for ozone smog.

The report says only Texas recorded more smog days, with 79. Data were not available for California, but Davis said that state is likely to have made the top of the list.

Davis said Tennessee air problems are worsened because its coal-fired plants are exempt from national emissions standards under the Clean Air Act of 1970.

The other smog factor is automobile emissions, which are increasing rapidly in Tennessee, Davis said.

“From an automobile standpoint, we have a relatively high growth rate in total vehicle miles traveled in Tennessee, which is growing at a rapidly increasing rate,” Davis said.

Davis said the Tennessee Valley Authority, which operates several coal-fired boilers providing power to the region, is moving towards better emissions controls under orders from the U.S. Environmental Protection Agency. Such action would help reduce the state’s smog problem, he said.

“TVA is in the process of looking at controls for smog-forming emissions on certain power plants,” Davis said. “The impact certainly would be a reduction in emissions, and that translates into less smog.

“It would take some sophisticated modeling to determine the exact amount of reduction, but it would certainly be an improvement.”