Ozone Air Pollutant and Sources

A white cloud with the chemical formula for ozone, which is O3

Ozone, or O₃, is a gas composed of three atoms of oxygen in each molecule. Ozone in the upper atmosphere, or stratospheric ozone, occurs naturally and forms a protective layer that helps to shield us from the sun's harmful ultraviolet rays. Ozone near ground level, or tropospheric ozone, is a harmful air pollutant, and it is one of the main ingredients in photochemical smog.

Ground level ozone is not emitted directly into the air, but is created by chemical reactions involving nitrogen oxides, volatile organic compounds and oxygen. The energy for the reactions is provided by sunlight. The precursor pollutants that enter these reactions are emitted by cars, power plants, industrial boilers, refineries, chemical plants and other sources. The picture illustrates some of these sources and the complex reactions that form photochemical smog, including ground level ozone. More information is available on EPA's Ground-level Ozone Pollution webpage.

How ground level ozones form – see text prior to this image for text version. — Click to view a larger version of this image.

Missouri monitors ozone concentrations in the air at several locations across the state. Most of these monitoring sites are operated during March through October, because ozone formation in the air is more likely in the summer months. Click on the Air Monitoring Sites tab to learn more about these sites. Click on the Monitoring Data tab to learn more about the data collected from this sites.

For information about other ambient air pollutants that the department monitors, visit Air Pollutants and Sources.

Health Effects

Ozone can be good or bad for health and the environment depending on where it’s found in the atmosphere. Stratospheric ozone protects living things from ultraviolet radiation from the sun. Ground-level ozone can trigger a variety of health concerns.

Exposure to ground-level ozone can contribute to health and environmental problems. Ground-level ozone can irritate the eyes, nose and throat, damages lung tissue and aggravates asthma and other respiratory diseases, including bronchitis. 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 and many spend a large amount of time outdoors. Healthy adults can experience problems breathing, especially those who exercise or work outdoors when ozone levels are high.

For information about today's air quality forecast, visit Current Air Quality.

Monitoring Data

Ozone Pollutant

The primary National Ambient Air Quality Standard (NAAQS) for ozone is 0.070 parts per million (ppm) averaged over eight hours (annual fourth-highest daily maximum 8-hour concentration, averaged over three years). The federal ozone monitoring season runs from March 1 to Oct. 31.

Air Quality Analysis for Ozone - Weekly Monitor Data

Eight-hour ozone design values
Four highest eight-hour ozone values from beginning of ozone season
Running list of sites with exceedances from beginning of season
Monthly number of exceedances
Daily maximum average eight-hour concentration for each site from beginning of season
Map of Missouri's ozone monitoring sites

Preliminary one-hour ozone averages from all sites in parts per million

Preliminary eight-hour ozone averages from all sites in parts per million

Air Pollutant Design Values - Quarterly Report

Additional information about Ozone State Planning efforts

Flags in Air Monitoring Data

Technical issues can affect ability to deliver quality data. Access a table of symbols with explanation of the problems they represent.