Clearing the air

According to findings of a new report issued by the Environmental Protection Agency, emissions of six air pollutants nationwide have been cut by 25% over 30 years despite growth factors including a 161% increase in gross domestic product, increased energy consumption of 42% and an increase in vehicle miles traveled of 149%.

The six tracked pollutants in the report, titled "Latest Findings on National Air Quality: 2001 Status and Trends," were: nitrogen dioxide, ozone, sulfur dioxide, particulate matter, carbon monoxide and lead.

Measurements in recent years by EPA, states and tribes have revealed that the Southeast, Mid-Atlantic and Midwest regions and California have unhealthy air quality due to fine particles suspended in air. In the eastern U.S., particulates tend to come from power plants and motor vehicles, in combination with local emissions from transportation and other sources. High particulate concentrations come from mobile sources in California.

The report also stated that, of the six pollutants tracked, progress has been slowest for ground-level ozone. Ground-level ozone is formed when volatile organic compounds and nitrogen oxides react in the presence of heat and sunlight. Although emissions of the organic compounds have decreased 16% over the past 20 years, nitrogen oxide emissions have not been cut significantly.

The EPA stated that most of the 9% increase in nitrogen oxide between 1982 and 2001 was traceable to engines operated off-road and diesel-powered vehicles.