Geographic area which does not meet one or more of the National Ambient Air Quality Standards for the criteria pollutants designated by the Clean Air Act. Also any geographic region of the United States that the U.S. Environmental Protection Agency (EPA) has designated as not attaining the federal air quality standards for one or more air pollutants, such as ozone and carbon monoxide.
Any geographic area that has not met the requirements for clean air as set out in the Clean Air Act of 1990.
A locality where air pollution levels persistently exceed National Ambient Air Quality Standards. Designating an area as nonattainment is a formal rulemaking process and EPA normally takes this action only after air quality standards have been exceeded for several consecutive years.