The proposed revisions would establish a one-hour NO₂ standard at a level between 80 and 100 ppb, and retain the current annual average NO₂ standard of 53 ppb.

The EPA has proposed to tighten the nation's NO₂ air quality standard, the agency announced late Monday, June 29. The proposed revisions would establish a one-hour NO₂ standard at a level between 80 and 100 ppb, and retain the current annual average NO₂ standard of 53 ppb. The agency also proposed to 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.

"We're updating these standards to build on the latest scientific data and meet changing health protection needs," said EPA Administrator Lisa P. Jackson. "In addition to limiting annual average concentrations, we're preventing high NO₂ levels for shorter periods of time and adding stronger monitoring in areas near roadways, where the highest levels of NO₂ are often found. This will fill gaps in the current standard and provide important additional protections where they are needed most."

The 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 2009: one in Los Angeles and one in the Washington, D.C. area. The agency said will provide details on the public hearings in a separate notice issued later this summer.

In a court decision that canceled the agency's last NO_X program, the EPA was directed to issue a final decision on the NO₂ standard by Jan. 22, 2010.