The U.S. Environmental Protection Agency (EPA) tightened the one-hour standard for measuring emissions of nitrogen dioxide (NO2), but left the annual standard unchanged. The long-term exposure remains at a maximum of 53 parts per billion (ppb) while an acceptable short-term exposure limit is now 100 parts per billion. Short-term concentrations of NO2 were previously allowed to range from 100–200 ppb.
The EPA believes NO2 exposure has been linked to respiratory problems. The primary man-made sources for NO2 are motor vehicles, coal-burning power plants and factories. According to the EPA, all areas of the country currently meet the existing annual air-quality standard, and ambient concentrations of nitrogen dioxide dropped 41% between 1980 and 2006.
The agency will now, however, require more monitors along busy roads and in large urban areas by 2013. It will then collect data for several years to determine which areas are not in compliance with the new standard and whether additional steps are necessary to reduce emissions.
Questions: Contact Stuart Gosswein.