Air Quality Management - National Ambient Air Quality Standards (NAAQS) for Criteria Pollutants

The EPA established the National Ambient Air Quality Standards (NAAQS) for six common air pollutants, called criteria pollutants. The criteria pollutants are: carbon monoxide (CO), nitrogen dioxide (NO2), sulfur dioxide (SO2), lead (Pb), particulate matter (PM), and ozone (O3). Ambient air is the air to which the general public has access, as opposed to air within a facility or at a smokestack. The NAAQS is based on comprehensive studies of available ambient air monitoring data, health effects data, and material effects studies. NAAQS regulates criteria pollutants by setting ambient air concentration and time standards and taking actions to attain these standards. Most pollutants regulated by the NAAQS have two limits. One limit, the "primary" standard, protects everyone including children, people with asthma, and the elderly from health risk. The other limit, the "secondary" standard, prevents unacceptable effects on the public welfare, e.g., unacceptable damage to crops and vegetation, buildings and property, and ecosystems. The primary and secondary standards for each of the criteria pollutants are shown in Table 3. Each NAAQS corresponds to a specific averaging time, and some pollutants have standards for more than one averaging time. The averaging time is the time period over which air pollutant concentrations are averaged for the purpose of determining attainment with the NAAQS.

A designation is the term EPA uses to describe the air quality in a given area for any of the criteria pollutants. A geographic area that meets or does better than the primary standard is called an attainment area; areas that do not meet the standards, or contribute pollution to nearby areas that do not meet the standards, are called nonattainment areas (NAAs). An area may be designated attainment for some pollutants and nonattainment for others. An unclassifiable area is any area that cannot be classified on the basis of available information as meeting or not meeting a national primary or secondary ambient air quality standard for the pollutant. Compliance with the NAAQS has been the driving force behind most air pollution regulatory programs. State governments have the primary responsibility for achieving compliance with the NAAQS. The principle mechanisms for achieving this goal are the State Implementation Plans (SIPs) and Tribal Implementation Plans (TIPs).