Outdoor Air Pollutants


The Clean Air Act, as amended in 1990, requires the federal Environmental Protection Agency to set National Ambient Air Quality Standards for six common air pollutants:

These pollutants can harm your health and the environment, and cause property damage. EPA calls these pollutants "criteria" air pollutants because it regulates them by developing human health-based and/or environmentally-based criteria (science-based guidelines) for setting permissible levels. The set of limits based on human health is called primary standards. Another set of limits intended to prevent environmental and property damage is called secondary standards.

Of the six pollutants, particle pollution and ground-level ozone are the most widespread health threats.  National Ambient Air Quality Standards are reviewed periodically by the EPA, with input from the Clean Air Scientific Advisory Committee (CASAC) and other stakeholder groups, and can be revised. 



What is a Nonattainment Area?

The Clean Air Act and Amendments of 1990 define a nonattainment area as a locality where air pollution levels persistently exceed National Ambient Air Quality Standards or a locality that contributes to ambient air quality in a nearby area that fails to meet 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. Nonattainment areas are given a classification based on the severity of the violation and the type of air quality standard they exceed.
Image of Ozone Pollution


Montgomery County and Nonattainment

Montgomery County's air quality planning falls within the Washington Metropolitan Council of Government's region air quality planning. The Washington region is a non-attainment area for ozone and fine particulate matter (PM2.5).

The region has had to demonstrate, through the development of a State Implementation Plan, or SIP, a plan of action to improve air quality in the region so that it would attain the NAAQS by a certain set date.

Efforts made based on the particulate matter and ozone SIPS have shown positive results. In May 2013, the Council of Governments petitioned the EPA to no longer classify the region as non-attainment for particulate matter.

State Implementation Plans: