Criteria Pollutants

The Environmental Protection Agency (EPA), in accordance with the federal Clean Air Act, has set National Ambient Air Quality Standards (NAAQS) for six common pollutants to protect human health and welfare. These six pollutants, called “criteria” pollutants, are carbon monoxide, lead, nitrogen dioxide, ozone, particulate matter, sulfur dioxide. For more information about each criteria pollutant, please click on the buttons at the top of this page.

National Ambient Air Quality Standards (NAAQS)
EPA sets each NAAQS after years of study and review of medical studies. The NAAQS include primary and secondary standards. Primary standards provide public health protection, including protecting the health of “sensitive” populations such as asthmatics, children, and the elderly. Secondary standards provide public welfare protection, including protection against decreased visibility and damage to animals, crops, vegetation, and buildings. For a table of the current NAAQS, please visit EPA’s NAAQS Table.

Each standard differs in form based on how the pollutant affects human health or welfare. An example of a NAAQS is the 24-hour PM2.5 health-based standard of 35 mg/m3 (micrograms per cubic meter); this means some people may experience health effects if exposed to a full day of PM2.5 concentrations averaging more than 35 mg/m3.

Attainment Status and Trends
The Clean Air Act (CAA) Amendments of 1990 established rules for designating areas of the country in attainment or nonattainment of the NAAQS. EPA defines an area as attainment or nonattainment based on a design value, which is usually calculated from measured concentrations over a three-year period. An area is said to be “in attainment” if the design value is equal to or below the NAAQS threshold; it is “in nonattainment” if the design value is above the NAAQS.

The 1990 CAA Amendments require states to submit a state implementation plan (SIP) for nonattainment areas; a SIP is a set of technical analyses and documents outlining how the state plans to achieve attainment. If a previous nonattainment is re-designated to attainment due to improved air quality, it becomes a maintenance area and requires maintenance plans to ensure it continues to meet the standard. Learn more on NHDES’ State Implementation Plans.