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( Article Type: Explanation )

The ozone layer occurs in the upper atmosphere (strato-sphere) surrounding the earth. It protects life on earth by absorbing most of the harmful ultra-violet rays (such as UV-B radiation) coming from the sun before they reach the earth. This layer is therefore very important in protecting all living things from UV-B radiation. This radiation can be very damaging to plants and animals as it suppresses the growth and functioning of the immune system. UV-B radiation is also a major cause of skin cancer and so any destruction of the ozone layer increases the health risk for humans. The layer is destroyed by ozone depleting substances (ODS), which are chemicals such as CFCs (chlorofluorocarbons) and halons, used in fridges, aerosols, fire extinguishers and released through other industrial processes.

Whilst ozone in the stratosphere performs a useful function, ozone in the lower atmosphere (troposphere) is harmful to living things at high concentrations and is thus a pollutant. Tropospheric ozone pollution is caused by the reaction of volatile organic compounds (VOCs) with sunlight, causing a photochemical reaction. Ozone is an unstable form of oxygen (the molecule contains three oxygen atoms) and is found in the atmosphere. The ozone in the stratosphere is more stable than tropospheric ozone and forms the so-called ‘ozone layer’ between roughly 15 and 50 kilometres above the earth. The chemistry of the atmosphere is still not fully understood but it is known that the stratospheric ozone layer protects life on earth from the harmful effects of short wave (UV) radiation.

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