Breathing air containing ozone can reduce lung function and aggravate asthma and other respiratory problems, according to the Environmental Protection Agency (EPA). At ground level, ozone is a harmful air pollutant created by chemical reactions between nitrogen oxides (NOx) and volatile organic compounds (VOCs). This often happens when pollutants emitted by cars, power plants, industrial boilers, refineries, chemical plants and other sources chemically react in the presence of sunlight.

The Clean Air Act requires the EPA to set National Ambient Air Quality Standards (NAAQS) for ozone and other pollutants considered harmful to public health and the environment. With these standards in place, states, tribes and the federal government are held responsible for reducing ozone air pollution.

The EPA is required by the Clean Air Act to reevaluate the NAAQS every five years. After new or revised NAAQS are established, the EPA works to designate areas as meeting (attainment) or not meeting (nonattainment) the standard. States and tribes then have an opportunity to submit initial area designation recommendations within 12 months after the EPA has issued a new or revised NAAQS.

These ozone air quality designations are based on air quality monitoring data collected over the three most recent years. States have monitors in various regions where they anticipate high and low levels of ozone.

Once designated, states with nonattainment areas submit a state implementation plan including how they will achieve attainment. Nonattainment areas could be classified as marginal, moderate, serious, severe or extreme.

Latest EPA Reclassifications

The EPA has published final action for 11 ozone nonattainment areas previously classified as moderate for the 2008 ozone NAAQS of 0.075 parts per million. Here’s what the reclassification breakdown looks like:

  • Two moderate areas — Baltimore, Maryland, and Mariposa County, California — attained the standards by their applicable attainment date; thus, moderate status will be maintained.
  • Two moderate areas in Sheboygan County, Wisconsin, were granted a one-year extension to achieve attainment with the standard.
  • Seven moderate areas failed to attain the standard and are being reclassified as serious nonattainment areas. These areas will now be required to submit state implementation plan revisions and implement controls to satisfy the statutory and regulatory requirements for serious areas for the 2008 ozone standard:
    • Chicago-Naperville – Illinois, Indiana, Wisconsin
    • Dallas-Fort Worth, Texas
    • Greater Connecticut
    • Houston-Galveston-Brazoria, Texas
    • Nevada County – Western California
    • New York-North New Jersey-Long Island
    • San Diego County, California

Serious nonattainment areas have additional control measures to reduce emissions, such as decreased permitting thresholds and strict standards of performance. These seven newly designated serious nonattainment areas must submit state implementation plans by August 2020.


When project plans are complicated by nonattainment permitting requirements, options such as purchasing emission reduction credits or reducing internal emissions can deliver solutions for your project success.

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Beth Freymiller is an environmental project manager at Burns & McDonnell who specializes in air quality permitting and environmental compliance.