Ozone is a colorless gas that is a variety of oxygen.
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.