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The Clean Air Act requires the Environmental Protection Agency (EPA) to set National Ambient Air Quality Standards (NAAQS) for six principal pollutants called criteria air pollutants, which can be harmful to public health and the environment.
A few air pollutants, called criteria air pollutants, are common throughout the United States. These pollutants can injure health, harm the environment and cause property damage. Criteria air pollutants include carbon monoxide, lead, nitrogen dioxide, ozone, particulate matter, and sulfur dioxide.
The Clean Air Act identifies two types of NAAQS (40 CFR Part 50).
The standards for criteria air pollutants are as follows:
Particulate matter (PM) pollution
PM2.5 (fine particles)
PM10 (inhalable particles)
Process for new or revised NAAQS. After EPA sets a new NAAQS or revises an existing standard for a criteria air pollutant, the Clean Air Act requires EPA to decide whether areas throughout the country meet the new standards. Within a year of setting a new or revised standard for a criteria pollutant, states and tribes submit recommendations to the EPA as to whether an area is attaining the standard. They base these recommendations in part on current air quality data from monitors.
EPA works with the states and tribes and considers all this information. The agency then designates an area based on whether it meets the standards. If it meets or is cleaner than the national standard, it is called an attainment area. If it doesn’t meet the standards, it’s called a nonattainment area.
Once designations go into effect, state and local governments with nonattainment areas must make implementation plans describing how areas will attain and upkeep the standards to lower air pollutant emissions. Tribes may decide to make these implementation plans but are not mandated to do so.