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2014 Mecklenburg County State of the Environment Report

Ground-level Ozone

Ground-level Ozone indicatorOzone levels are improving. The 2008 change to the NAAQS ozone standard (from 0.08 to 0.07​5ppm) means that Mecklenburg County will be classified as nonattainment for ground-level ozone.



Ground-level Ozone
Ground-level ozone is the primary constituent of smog, and is the criteria air pollutant of greatest concern in Mecklenburg County. Ozone is not emitted directly into the air, but is created by chemical reactions between oxides of nitrogen (NOx) and volatile organic compounds (VOC) in the presence of sunlight. Under the Clean Air Act, EPA has set protective health-based standards for ozone in the air we breathe.

Mecklenburg County was designated as a non-attainment area for the ozone National Ambient Air Quality Standards (NAAQS) (0.12 parts per million) in March 1978 and remained non-attainment through the 1980's. Based on monitoring data collected from 1990 - 1992, Mecklenburg County was designated as attaining the 1979 NAAQS on July 5, 1995.

In July 1997, EPA revised the ozone standard to an 8-hour standard with a level of 0.08 ppm. The compliance value measured in the Mecklenburg County network from 2001-2003 was 0.098 ppm therefore on June 15, 2004, Mecklenburg County was designated non-attainment for the 8 hour NAAQS. Mecklenburg County demonstrated compliance with the 1997 ozone standard at the end of the 2010 ozone season with a compliance value of 0.082 ppm. In 2011 Mecklenburg County's compliance value remained below the 1997 ozone standard at 0.079 ppm. A Redesignation Demonstration and Maintenance Plan for the region was submitted to the U.S. Environmental Protection Agency (EPA) on November 2, 2011. The EPA announced on December 2, 2013 that it is taking final action to approve the state of North Carolina's request to redesignate the Charlotte area to attainment of the 1997 8-hour ozone standard. This action is based on air quality monitoring data for the three-year period of 2008, 2009, and 2010 that meets the standard. The area continues to attain this standard.

On March 12, 2008, EPA again significantly strengthened the NAAQS for ground-level ozon​​e. EPA revised the 8-hour "primary" ozone standard, designed to protect public health, to a level of 0.075 ppm. The 2010-2012 compliance value for Mecklenburg County was 0.083 ppm, which exceeds the level of the 2008 NAAQS.
What does this mean for my health?
The amount of air pollution that is measured is compared to a health-based National Ambient Air Quality Standard (NAAQS) and converted into an Air Quality Index (AQI) value. This AQI value can range from 0-300 and communicates the amount of air pollution that is measured and how that affects our health. The compliance value of 0.083 ppm is converted to an Air Quality Index (AQI) value of 119, as shown in the graph above. When the AQI value is higher than 100, the air quality has exceeded health-based standards set by the EPA and is considered Unhealthy for Sensitive Groups. Read more about the Air Quality Index and how it relates air pollution to your health.

For more information on this topic, see the links included or go to "Contact ​Us" on the MCAQ home page.

What you can do to reduce air pollution in Mecklenburg County

More Information:

Mecklenburg County Air Quality Ozone Information
NCDENR - Ozone - The Good and The Bad
Stationary Sources
Mobile Sources
Area Sources
Health Effects of Air Pollution

Return to Air Quality Chapter Page

The trends shown in the State of the Environment Report are not all based on tests of statistical significance. Data analysis, anecdotal evidence, and best professional judgment have been compiled to represent these trends. The State of the Environment Report takes a snapshot of important environmental indicators in an effort to educate the public while highlighting challenges, successes and the general direction of change for each indicator. For additional information on these indicators and the determination of trends, please follow the links and feel free to contact the appropriate resources.

Last updated 2/24/14