Ozone is a gas which is composed of three atoms of oxygen. The ozone concentration at earth surface is usually present in the range of 0.02 ppm to 0.04 ppm. Ozone varies globally with concentration of more than 1 ppm and is continuously present on upper atmosphere.
The pressure of ozone in the atmosphere plays as dual role. At ground level ozone enters the body through inhalation and exerts toxic effects directly on the lung. Exposure of ozone has been associated with being cancer, DNA breakage and visual impairment. However, the stratosphere ozone forms a protective shield against harmful UV radiation.
The atmospheric ozone is obtained in its two layers. The bottom layer extends up to 15 km from the earth and is known as troposphere; where as the top layer which extends from 15 to 50 km is known as stratosphere ozone.
Depletion of ozone layer has appeared, first over Antarctica in Northern hemisphere and Polar Regions. The primary cause for ozone loss is due to chlorofluorocarbons (CFCs). During the year 1980 and 1987 it was established that direct involvement of chlorine and some heterogeneous chemicals were responsible for depletion of ozone.
It has been established that various kinds of gases which are released in the atmosphere by human activity are main causes for depletion of ozone layer.
The stratosphere ozone is formed mist of equator which is displaced over the Polar Regions. It is because of this reason that the concentration of ozone is found to be maximum at poles. At these poles and Antarctic and Arctic regions the depletion of ozone has been found to be fastest. This is due to strong westerly winds around the poles moving at a speed of 90 to 100 metre per second.
Out of many reactions sequences which lead to the destruction of ozone, one of the most important reactions is associated with the breakdown of stable organic chlorine compounds of CFCs where air active chlorine atom can catalytically destroy ozone.
Accelerating ozone layer depletion has serious impact on most of the life forms. For every 10% depletion of the ozone layer, one can expect 20% increase in U.V. radiation arriving on earth. This radiation could change genetic character, after immune systems, damage crops, disrupt marine food web and enhance green house warming by affecting the CO2 absorption capacity of planktons in the ocean. The incidence of human cancer would increase and the sight of millions could be affected as more intense UV radiation damages eyes and causes cataracts.
Immune response may be depressed in people exposed to increased radiation levels, vaccination programmes may become less effective and infectious diseases may become more common and more severe. Plant growth may be inhibited and crop yields may be reduced. Adverse effects on nitrogen fixing bacteria in rice paddies may result in drastic drops in production.