U.S. District Judge Lacy Thornburg, ruling in a nationally watched case, said North Carolina had shown that untreated air pollution from three power plants in eastern Tennessee and one in Alabama harmed citizens in North Carolina and posed a public nuisance. Thornburg said the TVA had failed to install pollution controls in a timely manner, and he ordered installation of such controls.

The court rejected North Carolina's request to require that TVA install controls on seven other coal-burning plants more distant from North Carolina, saying the effect of pollution from those plants was not measurable in North Carolina.

North Carolina sued TVA in 2006, contending the pollution from its 11 coal-burning power plants in Tennessee, Alabama and Kentucky wafting across the border caused respiratory problems and threatened the health of millions of people. The state's environment and economy also are harmed by TVA's emissions, which pose a public nuisance, the state argued.

TVA, a federal government agency, operates the nation's largest public electricity-producing system, providing power to large portions of Tennessee, Kentucky, Mississippi and Alabama and small parts of western North Carolina and southwestern Virginia. TVA's 11 coal-burning plants range from 35 to 50 years old.