UV rays are very harmful to living things and can cause diseases like skin cancer and can also alter the climate drastically. The ozone layer protects us from these harmful rays and is essential for life on earth.
The ozone layer is not uniform throughout the earth; it is found in a thick layer at some places and a thin layer at others. If this layer becomes too thin, it cannot stop the UV rays from entering the earth and we say that a hole is formed in the ozone layer. Antarctica has the biggest ozone hole followed by the Arctic region and the Tibetan plateau. In these places, the layer was naturally thin, but over the years due to air pollution, these holes have grown bigger and thinner.
The blue region is the hole over Antarctica which has grown enormously since 1979.
The ozone layer is a thin layer in the atmosphere at an altitude of about 20-30 km that has a high concentration of ozone gas. It is made up of three atoms of oxygen and is represented as O3. Ozone (O3) is formed by the absorption of Ultra-Violet (UV) light by oxygen (O2) molecules. These molecules react with each other and form ozone (O3). In this process, they absorb the UV rays from the sun earth where they may damage many forms of life and prevent it from reaching the earth’s surface. The high energy ultraviolet radiation splits ozone into molecular and atomic oxygen. Thus, ozone layer acts as UV filter – the earth’s natural sunscreen.
Reduction in the concentration of ozone layer is called ozone depletion.
The major cause of the thinning of the ozone layer is the use of chloro-fluoro-carbons or CFCs such as carbon tetrachloride, CC13; dichlorodifluoromethane, CC12F2 and Hydro- Chloro-fluoro-carbons or HCFCs. They are compounds of chlorine, fluorine, and carbon such as CF3Cl, CHCl2F etc. These are used as refrigerants in refrigerators, ACs, and cooling plants. These molecules can destroy (O3) molecules and hence make the (O3) layer thinner.
Besides, nitrogen oxides such as nitrous oxide are also very reactive to (O3) and are also responsible for holes in the ozone layer. These molecules are released by burning fossil fuels by cars and especially airplanes which fly near the ozone layer.
Depleting ozone layer allows more ultraviolet (UV) radiations to pass through it, which reach the earth’s surface. Since 1975, the hole has increased in size due to depletion in the ozone layer. Reductions of up to 70% have been found in some areas.
These UV rays cause various harmful effects on human beings, animals, plants and environment such as:
Countries around the world have agreed to stop the production and use of CFCs and HCFCs and have also introduced the application of bio-control agents for controlling the plant pests. The Montreal protocol was signed in January 1989, to limit the use of CFCs and HCFCs. 197 countries have ratified this protocol which has reduced CFC production by 98% today. It remains the most successful environmental treaty to this date.
There are better CFC free refrigerants available now that do not pollute the atmosphere. Almost all the air-conditioners and refrigerators do not contain harmful pollutants. The depletion of the O3 layer has almost stopped today and there are signs that it can grow back.
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