In a report released April 30 by the EPA, U.S. air pollution levels continued to decline in 2006 over the long term. Emissions of six key pollutants have dropped by more than half since 1970 and the national average concentration for each criteria pollutant is below the level of its air quality standard.

During the same time period: the U.S. gross domestic product increased 203 percent, vehicle miles traveled increased 177 percent, energy consumption increased 49 percent, and U.S. population grew by 46 percent. In addition, emissions of air toxics in 2002 were 35 percent lower than 1990 levels.

Under the Clean Air Act, the EPA set national air quality standards for six key pollutants, including NO₂, ozone, SO₂, particulate matter and lead. Each year, the agency examines the levels of these pollutants in the air and the emissions from various sources to see how both have changed over time and to summarize the current status of air quality. While national average concentrations of the six key pollutants are below national standards, results vary by site. Annual pollution levels at some monitoring sites do remain above one or more of the national air quality standards, with ozone and particulate matter remaining as the most persistent problems.

Visit: www.epa.gov/airtrends/econ-emissions.html.