Ozone (O3) is produced by the combination of three oxygen atoms (O). The concentration of atmospheric ozone is small, approximately 3 molecules of ozone for every ten million air molecules. Through absorption of ultraviolet radiation (UV), ozone plays a fundamental role in the radiation budget and life on earth. Absorption of UV energy causes a heating that produces the increasing temperature with altitude, a characteristic feature of the stratosphere. Ozone absorption of UV also keeps this harmful radiation from reaching the surface.
Ozone primarily occurs in the stratosphere though some ozone, approximately 10% of the total amount, exists in the troposphere. The maximum ozone concentration is between 20 and 25 kilometers (about 12 to 15 miles) above the surface. The layer of maximum ozone concentration in the stratosphere is referred to as the ozone layer. The altitude of the ozone layer varies with latitude. Stratospheric ozone is beneficial to life because it absorbs ultraviolet radiation that is biologically damaging. Absorption of UV energy heats the atmosphere and is responsible for the temperature inversion observed in the stratosphere.
Ozone is a chemically active molecule and is considered a corrosive gas. High levels of ozone can damage plant and animal tissues when they come into contact with ozone due to chemical reactions. When atmospheric ozone is present near the surface it is a pollutant. High concentrations of ozone reduce crop production and are detrimental to human health. Thus, while decreased amounts of stratospheric ozone are dangerous to human health, decreased amounts of tropospheric ozone near the surface are beneficial! Ozone is a major component of smog, a type of air pollution that forms during the day.
In addition to strongly absorbing radiation at ultraviolet wavelengths, ozone also absorbs and emits electromagnetic radiation at wavelengths in the vicinity of 9.6 microns.