The Missouri Department of Natural Resources monitors ozone across the state during the ozone season, which begins April 1 and ends October 31. Naturally occurring ozone in the upper atmosphere protects the earth from the sun's harmful rays. Ground-level ozone, commonly known as smog, is a gas that is created when pollution from vehicles, businesses and power plants combine in the presence of sunlight. The pollutant is formed when heat and sunlight mix with volatile organic compounds, or VOCs, and nitrogen oxides, or NOx, in the lower atmosphere. Typically, ozone pollution is more of a problem in the hot summer months because sunlight and warm temperatures speed up the formation of ground-level ozone.

EPA regulatory actions related to ground-level ozone.

Health Effects

Exposure to ground-level ozone can contribute to health and environmental problems. Ground-level ozone is an irritant that damages lung tissue and aggravates respiratory disease. Ozone can trigger a variety of health problems. Those most susceptible to ozone include children, the elderly and individuals with pre-existing respiratory problems. Children are at increased risk from exposure to ground-level ozone because their lungs are still developing. Healthy adults can experience problems breathing, especially those who exercise or work outdoors.

Reducing Ozone

Simple everyday steps can help reduce the emission of harmful pollutants that are derived from vehicles and coal-fired power plants that produce our energy. These emissions contribute to the formation of ground-level ozone.

Ozone-reducing activities include:

  • Use mass transit, carpool, bike or walk.
  • Do not top off gas tanks. Stop at the first click.
  • Do not use gas-powered lawn equipment on hot, sunny days with little or no wind. Consider waiting until early evening to mow your lawn.
  • Conserve energy by turning off lights and appliances when leaving a room to reduce emissions from power plants. Purchase Energy Star® appliances.
  • Set goals to reduce utility bills by two percent. This can save money and protect air quality.
  • Keep tires properly inflated.

For even more tips, visit

Ozone Monitoring

The department maintains and collects data from air monitors across Missouri to see if Missouri’s air quality meets the Environmental Protection Agency’s National Ambient Air Quality Standards (NAAQS). If an area monitors or contributes to violations of the ozone standard, actions must be taken to reduce the emissions that contribute to the formation of ground-level ozone. The department works with affected areas to develop emission reducing measures that are the most effective in terms of cost and emission reductions.

Ozone Monitoring Data

U.S. Ozone Review 2013, 2012 and 10 year average

Eight-Hour Ozone Information

  • The 2008 8-Hour Ozone NAAQS

On September 22, 2011, the U.S. Environmental Protection Agency released a memorandum to clarify for states the status of the 2008 Ozone NAAQS. In this document, EPA explicitly stated that the current standard is 0.075 parts per million, or 75 parts per billion. EPA then moved forward with boundary designations under the 2008 NAAQS. EPA is expected to release a SIP requirements rule in the Fall of 2014 that will explain the State Implementation Plan (SIP) submittals required of states that contain nonattainment areas under the 2008 standard.   

  • Boundary Designations for the 2008 Ozone NAAQS

In March 2009, Missouri submitted its original boundary recommendation for the 2008 ozone NAAQS to EPA, based on the ozone air quality monitoring data for the three years of 2005–2007.  Then in December 2011, Missouri updated the boundary recommendations based on air quality data for the three years of 2008–2010.

On May 21, 2012, EPA finalized the area designations. The St. Louis area was designated nonattainment area and classified as marginal for the 2008 ozone standard. The boundaries of the Missouri portion of the nonattainment area remained the same as for the 1997 ozone standard but its classification changed from moderate. Marginal nonattainment areas have until December 31, 2015 to attain the 2008 Ozone NAAQS.

Since the St. Louis Ozone Area is a bi-state nonattainment area, Illinois went through a similar designation process for its portion – the Metro-East side of the St. Louis area. For the Illinois portion under the 2008 ozone NAAQS, Jersey County is no longer designated as nonattainment as it was for the 1997 ozone standard. For more information on EPA’s final state designations for the 2008 ozone NAAQS, click here.

Information about past and present boundary designation processes for recently revised NAAQS is available on Missouri’s NAAQS Boundary Designations webpage.

  • State Implementation Plans for Ozone

After a new NAAQS is finalized, States have three years to develop an infrastructure SIP that demonstrates the State’s ability to implement, maintain, and enforce the NAAQS.  The State developed the infrastructure SIP for the 2008 ozone NAAQS and submitted it to EPA for approval in June 2013.

Because the St. Louis area was classified as a marginal nonattainment area, additional nonattainment related SIP elements must be submitted to EPA. As new SIP elements are released for public notice, they will be available for public review and comment online at the State Plans on Public Notice webpage. 

For information regarding past SIP submittals addressing ozone, including SIPs submitted to address the previous 1-hour standard and the 1997 8-hour standard, click the link below.

Ozone State Implementation Plan

Other Ozone Links

Air Quality
APCP Calendar of Events
The Darker Side of Ozone
EPA Ozone webpage
Help fight ozone this summer!
Kansas City AirQ - Kansas City Air Quality Forecast
Missouri Air Quality Monitoring Network
Other Environmental Links
Ozone - Something you can easily reduce!
St. Louis Regional Clean Air Partnership - St. Louis Air Quality Forecast