A federal appellate court has rejected  a 2004 Environmental Protection Agency ozone rule and directed it to rewrite the regulation. The decision is a setback for EPA and a victory for the California air pollution control agency that challenged the rule and for environmental groups that feel EPA’s action weakened air pollution standards. 

In a Dec. 22 decision, a three-judge panel of the Court of Appeals for the District of Columbia Circuit ruled unanimously that EPA’s regulation violated the Clean Air Act, stating that EPA’s interpretation of the law “in a manner to maximize its own discretion is unreasonable because the clear intent of Congress...was to the contrary.” The case is South Coast Air Quality Management District v. EPA.

The 1990 Clean Air Act amendments set up a new system for regulating ozone and five other pollutants and included a set of graduated requirements for localities that failed to comply with standards for ozone. The law set the ozone mark at 0.12 parts per million, using the yardstick of maximum average concentration for a one-hour span in a calendar year.

In 1997, EPA issued a new ozone standard, 0.08 ppm averaged over eight hours, thus changing “the measuring stick and the target,” the court said.

In April 2004, EPA issued another rule, saying it would withdraw the one-hour ozone standard a year after designations of localities that failed to meet the eight-hour mark became effective. That rule also said the more stringent Clean Air Act requirements would apply only to areas falling short of both the eight-hour and one-hour ozone standard. 

EPA claimed the changes would put more areas under “more flexible provisions” of the law and give states “greater discretion in determining the mix of controls needed to expeditiously attain the eight-hour” level, the ruling says.

Jennifer Wood, EPA’s press secretary, says the agency “is committed to ensuring our nation’s ozone air-quality standards are implemented to protect public health and the environment.” She says EPA officials will consider whether to ask the court to rehear the case.