Ozone Basics and Health Effects

Ozone (O₃) is a colorless gas found both in the Earth's upper atmosphere and at ground level. It is a very active form of oxygen that reacts rapidly and strongly with living tissues, plant-derived fabrics, dyes, rubber and many other man-made materials. Ozone has no odor except near high energy sources such as strong electrical arcs, sparks or close to a lightning strike. Ozone can be good or bad, depending on where it is found.

Good ozone

Ozone occurs naturally in the Earth's upper atmosphere, 10 to 30 miles above the Earth's surface. Ozone this high forms a layer that protects life on Earth from the sun's harmful ultraviolet rays. Find out more about this "good" ozone by following the links below.

Bad ozone

In the lower atmosphere, ozone is harmful to health. At ground level, ozone is created by a chemical reaction between nitrogen oxides (NOx) and volatile organic compounds (VOCs) in the presence of heat and sunlight.

Vehicle exhaust, industrial emissions, gasoline vapors and chemical solvents are some major sources of NOx and VOCs that form ozone. Wind can carry ozone hundreds of miles from its source. Ozone may damage plants and trigger health problems even at low levels -- people with respiratory illnesses such as asthma are most affected. Peak ozone levels typically occur during hot summertime conditions.

To reduce ground-level ozone, the DNR regulates NOx emissions from power plants and industrial combustion sources, requires low-emission vehicles and cleaner gasoline, and reduces VOC emissions by improving vehicle inspection programs. Many communities around the United States have "action day" or "clean air" programs in which businesses, schools, government agencies and citizen work together to voluntarily reduce air pollution.

The highest ozone levels in Wisconsin typically occur from mid-May to mid-September, especially in hot hazy weather with southerly winds. Depending on the weather, ozone can remain in an area several days, with the highest levels building up in the afternoon and continuing into the evening. High ozone concentrations are more common in southern Wisconsin than in the north.

It was once believed that unhealthy levels of ozone were confined to urban areas. However, in recent years the WDNR has measured ozone levels exceeding national health standards in some of Wisconsin's rural areas as well. These rural concentrations may result from the transport of ozone and emissions contributing to ozone formation over long distances, indicating the regional (rather than local) nature of this air pollution problem.

Ozone Basics and Health Effects

Good ozone

Bad ozone

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