The 1990 Clean Air Act is the most recent version of a law first passed in 1970 to clean up air pollution. This law requires the Environmental Protection Agency (EPA) to set National Ambient Air Quality Standards for ground-level ozone (and five other pollutants) that are harmful to public health and the environment.The six (6) common air pollutants (also known as “criteria pollutants”) are found throughout the United States. They are particle pollution (often referred to as particulate matter), ground-level ozone, carbon monoxide, sulfur oxides, nitrogen oxides, and lead. Of the six pollutants, particle pollution and ground-level ozone are the most widespread health threats. For information about these common pollutants, visit EPA’s website at

Ground Level Ozone and “Non-Attainment”

Areas that violate air quality standards for ozone are designated by EPA as non-attainment. The Greater Charlotte Region, like other North Carolina urban areas, has often exceeded federal health standards for ozone and has been designated “non-attainment.” Breathing ozone can trigger a variety of health problems including chest pain, coughing, throat irritation, and congestion. It can worsen bronchitis, emphysema, and asthma. Ground-level ozone also can reduce lung function and inflame the linings of the lungs.

What is Ozone? Ground-level ozone is the main ingredient of smog. The two chemical emissions that combine, in the presence of sunlight, to create ozone are nitrogen oxide (NOx) and volatile organic compounds (VOCs). On the east coast, the primary sources that create ground level ozone are local emissions from vehicles and stationary sources.

National Ambient Air Quality Standards (NAAQS)

Mounting scientific health studies indicated that a more stringent ozone standard was necessary to protect human health and welfare. As a result, in 1997 EPA announced a more stringent ozone standard of 0.08 parts per million measured over an 8-hour period, the 8-hour ozone standard (since ozone is measured out to three decimal places, the standard effectively became 0.084 ppm as a result of rounding). Due to litigation and other factors, this standard became effective in June 2004.

Since that time, EPA has promulgated a new standard. On March 27, 2008 EPA announced that the 8-hour standard would be lowered to .075 parts per million to better protect the public’s health. The new lower standard became effective in May 2008. This resulted in an increased number of “high ozone days” in the summer of 2008 and going forward. The greater number of air quality alerts reflects the tighter standard, not a decrease in air quality. In addition, over the past several years, the EPA was reconsidering the 2008 standard and a more stringent .060-.070 parts per million threshold was expected. On September 2, 2011, however, President Obama sent a letter to the U.S. Environmental Protection Agency Administrator Lisa Jackson noting his lack of support for moving forward with issuing a new national ozone standard at this time, highlighting three key concerns: lack of predictability, the need for updated scientific evidence, and current activities are doing a lot to reduce air pollution and ozone. The Clean Air Act requires that the next review of this standard would have to occur by 2013.

Role of Transportation Planning and Air Quality

The Centralina Council of Governments is involved in the transportation linkages to air quality through the Centralina Clean Fuels Coalition and working with regional MPOs and RPOs. Centralina staff are involved in regional travel-demand modeling and conformity determinations as a part of the transportation plans for the region. Centralina staff can put you in touch with the correct transportation planning staff for your area if you want to learn more about the linkages between transportation and air quality.

If you have any questions, please contact:

Jason Wager, Planning Program Supervisor

Phone: (704) 348-2707 or

Links to more air quality information

US EPA Air and Radiation

North Carolina Division of Air Quality

Mecklenburg County Air Quality

NC Air Awareness Program

NC Sustainable Energy Association

NC Clean Energy Technology Center