EPA proposes hourly for nitrogen dioxide

29 June 2009 — The U.S. Environmental Protection Agency is proposing adding a one-hour nitrogen dioxide (NO2) air quality limit of between 80 to 100 parts per billion (ppb). EPA would retain the current annual average NO2 standard of 53 ppb.

The proposed rule would add NO2 monitoring within 50 meters of major roads in cities with at least 350,000 residents and continue monitoring “area-wide” NO2 concentrations in cities with at least 1 million residents.

The proposed standards and additional monitoring requirements would reduce people’s exposure to high, short-term concentrations of NO2, which generally occur near roadways.

EPA said current scientific evidence links short-term NO2 exposures, ranging from 30 minutes to 24 hours, with increased respiratory effects, especially in people with asthma.

EPA first set standards for NO2 in 1971, setting both a primary standard to protect health and a secondary standard to protect the public welfare at 53 ppb, averaged annually. Annual average NO2 concentrations have fallen by more than 40 percent since 1980. EPA said all areas in the United States are well below the current (1971) NO2 standards with annual averages ranging from 10 to 20 ppb.

EPA will accept public comments for 60 days after the proposal is published in the Federal Register. The agency will hold two public hearings in August: one in Los Angeles and one in the Washington, D.C. area. EPA said it must issue a final decision on the NO2 standard by Jan. 22, 2010.