The Environmental Protection Agency sets permissible levels, known as the National Ambient Air Quality Standards, 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.

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