Ozone is a form of oxygen that has three atoms (O3) rather than the more common two atoms (O2).
It is created in the upper atmosphere by the action of solar radiation on oxygen molecules.
It is found in the form of a thin layer in the stratosphere between 15 to 48 kilometre.
About 90% of all atmospheric ozone is found in this layer.
Ozone constitutes only less than 0.002 percent of the volume of the atmosphere.
However, its role is very critical as far as a life on the earth is concerned.
It strongly absorbs ultraviolet radiation from the sun.
Ultraviolet radiation is biologically destructive in many ways.
Ultraviolet radiation causes skin cancer and cataracts, suppresses the human immune system, diminishes the yield of many crops, and disrupts the aquatic food chain by killing micro-organisms on the ocean surface and many other negative effects which are still undiscovered.
Depletion is mainly caused by chlorofluorocarbons (CFCs), halons, methyl chloroform and carbon tetrachlorides.
These chemical substances are mainly either chlorine or bromine which can reach the stratosphere and catalytically break down ozone into oxygen.
Not only is the ozone layer thinning, in some places it has temporarily disappeared.
A hole in the layer has developed over Antarctic since 1979 and that hole has persisted for a longer and longer time every year.
In 1988, an ozone hole was found over the Arctic for the first time and it too has lasted longer and longer each year since then.
Since the last two decades, certain actions have been initiated at global level.
Among these Montreal Protocol of 1987 and London Conference of 1992 are important.
In both these conferences it was decided that the developed countries would totally ban CFC production by 2000 and the developing countries by 2010AD.