The Environmental Protection Agency sets permissible levels for six common air pollutants: ozone, lead, particulate matter, sulfur dioxide, carbon monoxide and nitrogen dioxide. EPA bases these levels, or  standards, on the concentrations at which pollutants become health and environmental hazards. These standards are known as the national air ambient quality standards (NAAQS).

The Missouri Department of Natural Resources maintains approximately 50 air monitors across the state to track concentrations of these six common air pollutants as well as many other pollutants. To access an interactive map depicting the network, click on the partial map at right.