Health and Environmental Effects
Reducing Ozone
Ozone Monitoring
Eight-Hour Ozone Info

Depending on the location of ozone in our atmosphere, it can be harmful or helpful. Ozone occurs naturally in the upper atmosphere, where it protects Earth from the sun's harmful ultraviolet rays. However, in Earth's lower atmosphere, ground-level ozone can hurt the environment and harm people and animals. At this level, ozone does not occur naturally; in fact, it is created when pollutants emitted by cars, power plants, factories, and other sources react chemically in the presence of sunlight. Specifically, heat and sunlight mix with volatile organic compounds, or VOCs, and nitrogen oxides, or NOx, to produce ground-level ozone. Typically, ozone pollution is worse during hot, dry summers because sunlight and warm temperatures speed up the formation of ground-level ozone.

Health and Environmental 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. The most susceptible segments of society include senior citizens and those with pre-existing respiratory conditions, such as asthma or emphysema. Children also are at increased risk from exposure to ground-level ozone because their lungs still are developing. In addition, healthy adults can experience problems breathing, especially if they exercise or work outdoors.

Ground-level ozone also may harm sensitive plants and ecosystems. Plants vary in their sensitivity to ozone, and some have shown no sensitivity. Depending on the ozone levels, sensitive plants may show stunted growth and/or yellowing. They also may die. Research is ongoing concerning the effects of ground-level ozone on humans and the environment.

Reducing Ozone

Simple everyday steps can help reduce the concentration of ground-level ozone. Adopting the following measures can help you reduce emissions of harmful pollutants from your vehicle and from coal-fired power plants that produce electricity.

  • Stop at the first click when getting gasoline. Do not top off your gas tank. This practice will ensure that your vehicle emits lower levels of gasoline vapors.
  • Use mass transit, carpools and bicycles. Walking is a great alternative to using your personal vehicle, too.
  • Avoid using gas-powered lawn equipment on hot, sunny days with little or no wind. Wait 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.
  • Aim to reduce utility bills by two percent, using the above tips and by lowering your thermostat in winter and raising it in summer. This can save money and protect air quality.
  • Keep tires properly inflated, which helps vehicles run more efficiently and burn less gasoline.
  • Consolidate trips to minimize the need to use your vehicle.
  • Avoid unnecessary idling. Use drive-through lanes at banks and restaurants. Turn off your engine while waiting to drop off and pick up passengers.

For more tips, access the department's publication "What You Can Do To Improve the Air."
STOP Idling. START $aving. Access the department's flier about anti-idling and its brochure.
To access related links, go to and

Monitoring of Ground-level Ozone

The Missouri Department of Natural Resources maintains and collects data from air monitors to determine whether our air quality meets standards set by the Environmental Protection Agency (EPA.) The department maintains approximately 50 monitors. Please see the department's interactive map of air monitors. Using the map, you can access the department's monitors for all pollutants, or you can limit your search by pollutant. Each dot on the map corresponds with an air monitor maintained by the department or by an industry source under the guidance of the department.

The current standard for ground-level ozone is 0.070 parts per million (ppm), or 70 parts per billion (ppb). The department works with areas that have difficulty meeting the standard to develop the most effective and economical measures for reducing concentration of ground-level ozone. During the last several decades, Missouri has made tremendous strides in reducing ground-level ozone; however, the EPA has tightened the standard several times since the passage of the Clean Air Act in the 1970s, a practice that continues to challenge government, industry and the public.

Ozone Monitoring Data

The department provides access to the data it collects from air-monitoring sites.

The U.S. Environmental Protection Agency tracks ozone data recorded by state monitors. Go to The charts, below, give an idea of the information available.




Eight-Hour Ozone Information

EPA sets standards for ground-level ozone and other pollutants. Called the National Ambient Air Quality Standards, these standards provide guidance for state and federal regulations. In 2015, EPA tightened the ozone standard to 70 parts per billion (ppb). For more information, see EPA regulatory actions related to ground-level ozone. When the EPA lowered the standard in 2015, the department's Air Pollution Control Program began working on its efforts to meet the new standard.

To learn about Missouri's efforts to attain these standards, you may read about boundary designations as well as Missouri's implementation plan.

Other Ozone Links

Air Quality Index - An explanation of the color-coded scale for air quality
The Darker Side of Ozone: An article about how ozone's effects differ, depending on its location in the atmosphere
EPA Ozone webpage
Kansas City SkyCast - Air quality forecast for Kansas City region
St. Louis Regional Clean Air Partnership - St. Louis Air Quality Forecast