Strengthened NO₂ Limit Proposed

EPA is proposing to strengthen the national air quality standard for nitrogen dioxide, a limit that has not been changed since it was established in 1971. Under a proposal released last week, the agency would, for the first time, set a short-term standard for NO₂ concentrations in outdoor air. EPA is considering a limit of between 80 and 100 ppb for a one-hour period. Meanwhile, the agency would retain the current NO₂ standard of 53 ppb, which is a yearlong average. EPA says a one-hour standard for NO₂ is needed because scientific studies link short-term exposures of between 30 minutes and 24 hours with increased adverse effects. "Breathing NO₂ can irritate the lungs, trigger asthma attacks, and lower the body's natural resistance to respiratory infections," says Norman H. Edelman, chief medical officer for the American Lung Association, a group favoring a short-term standard for the pollutant. Sources of NO₂ include vehicles, fossil-fuel-burning power plants, and industrial facilities.