ozone
Ozone is a form of oxygen in which each molecule consists of three atoms instead of two as in the common form. Its scientific formula is O3. Ozone is often produced when a charge of electricity passes through the air. For this reason people sometimes notice ozone's distinct, unpleasant smell after a thunderstorm or around electrical equipment.
Ozone is a pale blue gas that is explosive and poisonous. It is 11/2 times as dense as common oxygen. Ozone gas condenses into a dark blue liquid at -170° F (-112° C). This liquid freezes at -420° F (-251° C).
Ozone is used in several industries. Because it reacts more easily with other chemicals than common oxygen does, factories use it in several chemical reactions that require oxygen. Ozone also kills germs, making it useful for removing bad smells and sterilizing drinking water. Ozone is used to bleach color out of many substances as well.
Ozone is a common form of air pollution. Even very small concentrations in the lower atmosphere can irritate eyes, cause coughing, and aggravate asthma. Automobile exhaust combined with sunlight can increase the amount of ozone in the air. People in many large cities suffer from health problems related to high ozone levels.
Although ozone in the lower atmosphere is a pollutant, ozone that is about 15 miles (24 kilometers) above the Earth's surface protects people. The ozone in the upper atmosphere absorbs harmful radiation from the sun. This radiation can injure eyes, damage genes, and promote skin cancer and other diseases. In the 1980s scientists recognized that some chemicals commonly used in industry were destroying this protective ozone. They noted a “hole” in the upper ozone layer over Antarctica. In 1987 more than 20 countries signed an agreement to reduce the use of chemicals that damage the ozone layer.
