Despite the reductions, 146.2 million Americans live in counties where air quality concentrations violate EPA air quality standards, although the severity of air pollution episodes has decreased in these areas, according to the report, "Latest Findings on National Air Quality: 2002 Status and Trends."

The report summarizes air quality information and facility emissions data for the six criteria air pollutants: carbon monoxide, lead, nitrogen dioxide, ozone, particulate matter and sulfur dioxide. It notes that new acid rain data show the agency's market-based cap-and-trade program has succeeded in reducing sulfur and nitrogen oxide emissions from power plants.

The report, based on monitoring at thousands of sites across the country, focuses on national trends for the 20-year period from 1983 to 2002 and the 10-year period from 1993 to 2002. Because of the phase-out of leaded gasoline, lead emissions and concentrations have decreased sharply over the past 20 years, with the 2002 average lead concentration at 94 percent lower than in 1983.

The annual air trends report comes on the heels of an EPA final ruling on the New Source Review (NSR) permitting program that would allow thousands of electric power plants, petroleum refineries and manufacturing facilities to make some upgrades without installing expensive equipment to fight air pollution.

Industry representatives have hailed the new ruling while environmental groups and politicians contend that it will lead to dirtier air and contradicts the original intent of the NSR permitting program. Several states have pledged to file lawsuits to block the final rule.

For more on the EPA's ruling, see www.epa.gov/nsr. For more on EPA's latest air trends report, see www.epa.gov/airtrends.