EPA released the "Air Quality Criteria for Carbon Monoxide," a revision of the 1991 document.
The agency found that ambient (outdoor) concentrations in metropolitan areas of the United States have decreased significantly since the late 1980s.
This decline approximately follows the decline in motor vehicle emissions of carbon monoxide.
Exposure of the general population to carbon monoxide, particularly from indoor sources, cannot be precisely estimated at this time, according to EPA.
Under the Clean Air Act, carbon monoxide is one of six criteria pollutants for which EPA has established National Ambient Air Quality Standards.
Periodically, the agency reviews the scientific basis for these standards by preparing an Air Quality Criteria Document.
The document on carbon monoxide may be found at the EPA''s Center for Environmental Assessment Web site at www.epa.gov/ncea.
A notice of availability appeared in the Aug. 17 Federal Register.
by Virginia Sutcliffe