2 November 1999

In a last week ruling of October 29, the US Court of Appeals for the District of Columbia upheld the earlier decision remanding tougher National Ambient Air Quality Standards (NAAQS) for ozone and PM established by the Environmental Protection Agency (EPA) in 1997.

The 1997 regulation introduced a new ambient air standard for fine particulates of diameters below 2.5 µm (PM2.5), and tightened the existing standards for 10 µm particulate matter (PM10) 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 1997 standards were challenged by industry groups, which opposed the estimated high costs to comply. As a result of a law suit, which was led by the American Trucking Association, the standards were remanded as unconstitutional in a 2-1 vote by a three judge panel in May, 1999. That ruling was appealed by the EPA.

In last week decision, nine judges of the Court of Appeals reviewed the original appeals court decision and five agreed that the nation's clean air standards were constitutional. Because the Court has 11 active members - two of whom were absent - the original court's interpretation remanding the EPA standards was left standing.

The EPA said, it will now recommend that the Justice Department seek a review before the Supreme Court.

The NAAQS set the ambient air quality targets in the USA and influence all other federal and state emission regulations, including those pertaining to diesel and gasoline engine emissions.

Source: EPA