During oral arguments October 17, the U.S. Court of Appeals for the District of Columbia questioned the stringency of Environmental Protection Agency rules implementing fine particulate matter standards. Specifically, Judge David Tatel asked why the agency would set more stringent standards for fine particles than coarse particles but implement the former through a less rigorous process. Petitioners argue that the standards should be implemented through a different section of the Clean Air Act, which would require tougher controls.