The Clean Air Act is the most sweeping of all the federal environmental laws, affecting most U.S. residents and businesses.
States carry out most of the enforcement powers under the federal standards.
A surprise court ruling in May 1999 has called into question how EPA set its new stricter air quality standards for ozone and particulate matter. The ruling threatens EPA s plan to change the way ozone attainment is measured, going from the peak level reached in any one hour to the much tougher measurement of averaging ozone levels over an eight-hour period. EPA began phasing out the one-hour standard in 1997, citing scientific reviews that indicated it did not adequately protect the public from adverse health effects. While EPA has asked for a rehearing in the federal case, the federal agency is keeping tabs on all ozone levels across Texas, including any exceedances of the eight-hour standard. EPA has proposed the one-hour standard be reinstated to regulate air quality while the new standard is in litigation.