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

In a Dec. 22 decision, a three-judge panel of the U.S. Court of Appeals for the District of Columbia Circuit ruled unanimously that EPA's rule violated the Clean Air Act, adding that the agency's interpretation of the statute "in a manner to maximize its own discretion is unreasonable because the clear intent of Congress…was to the contrary."

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

Then in 1997, EPA issued a new ground-level ozone standard, of 0.08 ppm, averaged over eight hours. The court said EPA thus changed "the measuring stick and the target."

In April 2004, EPA issued a new rule saying that it would withdraw the one-hour ozone standard one year after designations of localities that failed to meet the eight-hour benchmark became effective. The 2004 regulation also provided that the more stringent requirements under the Clean Air Act would apply only to localities that fell short of both the eight-hour ozone and the one-hour standard.

EPA explained that the changes would put more areas under "more flexible provisions" of the Clean Air Act and give states "greater discretion in determining the mix of controls needed to expeditiously attain the eight-hour" ozone standard, according to the court decision.

The South Coast Air Quality Management District in California, along with several states and environmental groups filed challenges to the 2004 EPA rule. None objected to the eight-hour standard, but "how quickly it must be attained and under what constraints," according to the decision.

In response to the court ruling, EPA press secretary Jennifer Wood said: "EPA is committed to ensuring our nation's ozone air quality standards are implemented to protect public health and the environment." She added, "EPA will review the decision and will consider whether or not to seek a rehearing."

Environmentalists praised the decision. "The decision is a victory for clean air," said David Baron, an attorney with Earthjustice. "The rule allowed more pollution in cities where the air was already unhealthy to breathe."

Sen. Barbara Boxer (D), the incoming chairman of the Environment and Public Works Committee, said, "Sadly, we have once again had to rely on the court to tell EPA how to read the text of the Clean Air Act in a way that protects people, not polluters. When the new Congress convenes, we will scrutinize EPAšs approach to clean air very carefully to ensure that the health of our families is protected." 

The case is "South Coast Air Quality Management District v. EPA." The organization that brought the case is the air pollution control agency for Orange County and parts of Los Angeles and two other southern California counties.