Air Quality

The Clean Air Act requires the United States Environmental Protection Agency (EPA) to set National Ambient Air Quality Standards (NAAQS) for six “Criteria Pollutants” – Particulate Matter, Ozone, Nitrogen Dioxide, Carbon Monoxide, Sulfur Dioxide, and Lead in order to protect human health and the environment from unsafe levels of these pollutants.
These pollutants are regulated through the EPA setting maximum limits on exposure levels that are reviewed periodically based on current science and health studies. Regions which are found to be out of compliance with those limits based on actual measurements of pollution at monitoring sites may be designated by EPA as a “Nonattainment Area.”

Air Quality

The Knoxville Region was formerly designated non-attainment for two of the criteria pollutants (ground-level ozone and fine particulate matter) under federal NAAQS. Fortunately, actual air quality monitoring data showed significant improvements in recent years and the Region has come into compliance with both standards such that EPA has formally re-designated the area back to attainment status. The Region is now considered a Maintenance Area for both ozone and fine particulate matter and it is important that we continue to reduce pollution to continue meeting the current NAAQS as well as possible future more stringent NAAQS that may be set.


One consequence of being designated as a nonattainment or maintenance area is the requirement to demonstrate “Transportation Conformity” for the TPO’s Plans and Programs. Transportation conformity is the link between air quality planning and transportation planning and its purpose is to ensure that federal funds will not be spent on projects that cause or contribute to any new violations of the NAAQS or delay timely attainment of the standards. Since portions of the nonattainment area extend beyond the TPO Planning Area, the TPO has entered an agreement with the Tennessee Department of Transportation to conduct the transportation conformity process for the entire nonattainment area.