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Ozone

An important greenhouse gas that consists of three atoms of oxygen bonded together, in contrast to normal atmospheric oxygen that consists of two atoms of oxygen. Ozone is found in both the stratosphere (about 90 per cent of the total atmospheric loading) and the troposphere (about 10 per cent). In the stratosphere, ozone also provides a protective layer shielding the Earth from ultraviolet radiation and subsequent harmful health effect on humans and the environment. In the troposphere, oxygen molecules in ozone combine with other chemicals and gases to cause smog.