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. 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 the process, they absorb the UV rays from the sun and prevent it from reaching the earth’s surface. This layer acts as UV filter – the earth’s natural sunscreen!
UV rays are very harmful to living things. It 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 thick at some places and thin 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. They are a serious cause of worry across the world.
You can see that blue region is the hole over Antarctica which has grown enormously since 1979.
Causes of Ozone Layer Depletion
The major cause of the thinning of the ozone layer is the use of chloro-fluoro-carbons or CFCs 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.
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.
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.
All is not lost though. The depletion of the O3 layer has almost stopped today and there are signs that it can grow back. This is because countries around the world have agreed to stop the production and use of CFCs and HCFCs. They have also introduced the application of bio-control agents for controlling the plant pests.In January 1989, the Montreal protocol was signed 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.
Today there are better CFC free refrigerants available that do not pollute the atmosphere. Almost all the air-conditioners and refrigerators you buy today do not contain these harmful pollutants.
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