15 May 1999

In a ruling of May 14, the tougher National Ambient Air Quality Standards (NAAQS) for ozone and particulate matter (PM) adopted in the USA in 1997 have been remanded by US Court of Appeals for the District of Columbia. The judges ruled by a 2-1 vote that the section of the Clean Air Act on which the EPA relied in coming up with the ozone and PM rules amounted to an "unconstitutional delegation of legislative power."

The court remanded the new particulate matter standard for fine particles (PM2.5) to the EPA for reconsideration. The particulate matter standard for coarse particles (PM10) was vacated. The decision did not set aside altogether the new ozone standards, but said they could not be enforced under the section of the Clean Air Act.

The 1997 regulation introduced a new standard for fine particulates of diameters below 2.5 µm (PM2.5), and tightened the existing standards for coarse particulate matter of diameter below 10 µm and for ozone. Diesel emissions, among other sources, contribute to PM2.5, as well as to ozone through the emission of ozone-forming NOx.

The standards were opposed by industry which estimated that the cost of complying could be as high as $45 billion a year. The ruling was hailed as a victory by a range of industry groups, led by the American Trucking Association, which had sued.

White House spokesman Joe Lockhart said the Clinton administration was "deeply disappointed" by the ruling, especially in view of the "court's explicit recognition that there is a strong scientific and public health rationale for tougher air quality protections." He said the administration was studying the ruling closely and would decide soon what to do next.

The EPA said that it "stands by the need for the health protections embodied by the clean air standards and the science behind them." The agency said it planned to recommend an appeal to the Justice Department. If it loses in the courts, the EPA said it would then call on Congress to "preserve these protections."