A five-year fight to establish tougher federal air quality rules is over.
A federal appeals court has issued a ruling allowing the U.S. Environmental Protection Agency to put in place tougher air quality standards, including requiring state and local governments to impose tougher controls on smog-causing chemicals and microscopic soot, including that from diesel exhaust.

The ruling follows a U.S. Supreme Court decision a year ago saying the federal government does not have to consider the financial costs when it writes rules to cut harmful engine exhaust. The Supreme Court ruling upheld some portions of the plan but sent other parts back to the lower court for further review - thus this week's appeals court ruling.
The 1997 plan fore the first time limited "fine particle" pollutants, including airborne soot from sources such as diesel trucks and power plants.
Plans to institute these rules proposed during President Clinton's administration received stiff opposition from several business groups, including the American Trucking Associations and the U.S. Chamber of Commerce, who argued the rules were enacted arbitrarily.
The EPA says it will develop a proposal by the summer for implementing the tougher clean air standards and identifying states that could be out of compliance in limiting pollutants.
While this most recent decision could be appealed, it most likely won't be due to the earlier Supreme Court ruling. ATA officials were not available to comment on the ruling.