The federal court told the EPA to review some factors related to pollution control standards in 2007. However, it left in place its January 2000 rule that limited nitrogen oxide emissions from power plants and industries that the EPA says are polluting northeastern states in particular.
Nitrogen oxide combined with hydrocarbons in the atmosphere creates ozone, or smog.
The EPA ruled that stationary sources of smog from a number of states and the District of Columbia were blowing into northeastern states, making it difficult for these states to meet clean air rules. The cited states include Indiana, Kentucky, Maryland, Michigan, Virginia and West Virginia. A spokesperson for the EPA said the agency welcomed the court decision and pledged to work on making more progress to clean the air and protect public health. Frank O'Donnell, executive director of the Clean Air Trust environmental organization, said the court ruling would help alleviate smog pollution in many locales. He noted that efforts by utilities owning coal-burning power plants had failed to persuade the court that EPA acted wrongly.