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Ozone

Ozone is a gas that plays different roles at different levels in the atmosphere. At lower levels it can be harmful to human and plant life. However, in the upper atmosphere (20 to 40 kilometres) it is vital for providing a barrier to ultraviolet (UV) rays, and thus protects the earth from the harmful effects of UV light.

This protective ozone shield is under threat when reactive human-made chemical pollutants, such as chlorine based chlorofluorocarbons (CFC) reach the stratosphere and cause the layer to deplete. Loss of stratospheric ozone between 2 to 4% per decade has occurred in mid-latitudes since the 1950s with emergence of a hole in the ozone layer over Antarctica in the 1980's.

Use of ozone depleting substances has been gradually phased out under the 1987 UN Montreal Protocol and it is now believed that stratospheric ozone levels are beginning to recover. Scientists have been able to measure a slowdown in the accumulation of chlorine in the atmosphere. However the hole is influenced by climatic conditions as well as pollution so it will take years to accurately ascertain the rate of change.

Last Updated: Friday 27 May, 2005

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