It is a health hazard causing damage to human health, the environment, crops, and a wide range of natural and artificial materials. Asthmatics and children are most at risk. The chance of experiencing adverse health effects from elevated ozone levels increases during heavy exercise or outdoor activity. Ground-level ozone can also damage trees, plants, and reduce visibility. It is also a product of reactions between chemicals that are produced by burning coal, gasoline, other fuels, and the chemicals found in paints and hair sprays.
Oxidation occurs readily in the presence of sunlight.
Motor vehicles and industries are major sources of pollutants that cause ground-level ozone. Certain cities with high levels of ground-level ozone have started a program called Ozone Action Days. The voluntary initiative was put in effect by cooperative efforts among government, environmental, and business organizations in order to reduce ground-level ozone. Ozone Action Days are most often on hot days, above 90 degrees Fahrenheit, with little or no wind blowing. Predictions that a day may be an Ozone Action Day are announced on television and radio news prior to the day to warn the general public that their actions are especially important in preventing air pollution on those days.