Tag: global environmental change

• An ozone hole is depletion of the ozone layer which is present in the stratosphere region around 26-30kms above the Earth surface. It was first detected in the stratosphere over Antarctica.
• It is caused by chlorofluorocarbons (CFCs) found in air conditioners, aerosol spray cans, refrigerants, etc. CFCs can not be removed in the troposphere and moves in the stratosphere layer where it reacts with ozone, thereby releasing of free chlorine atoms and causes the ozone layer to deplete. 

When the oxygen-depleting substances like CFCs, HFCs, methyl bromide etc. find their way to the stratosphere, the UV rays spilt them to release the reactive species of chlorine and bromine. These reactive species react with the ozone to release the oxygen, thereby causing the depletion of ozone. The ozone hole is the place where the thickness of the ozone layer is very thin and the concentration is less than 220 DU. It is seen over Antarctica due to the process of polar vortex and formation of polar stratospheric clouds.

The main cause of ozone depletion and the ozone hole is manufactured chemicals, especially manufactured halocarbon refrigerants, solvents, propellants and foam-blowing agents (chlorofluorocarbons (CFCs), HCFCs, halons), referred to as ozone-depleting substances (ODS). the United States National Academy of Sciences concluded that credible scientific evidence supported the ozone depletion hypothesis[59] a few countries, including the United States, Canada, Sweden, Denmark, and Norway, moved to eliminate the use of CFCs in aerosol spray cans. The United States banned the use of CFCs in aerosol cans in 1978.[60] The European Community rejected proposals to ban CFCs in aerosol sprays.

Ozone or O$ _3$ is a triatomic gas that forms a layer in the upper part of atmosphere called the Stratosphere. It acts as a shield against harmful radiations of the sun.

Ozone layer is present in the stratosphere which absorbs the harmful ultraviolet radiation Ultraviolet rays cause heritable mutational changes. They have the capability to destroy plants and animals and can cause skin cancer, cataracts to human beings. Existence of life on earth is possible only because of the presence of ozone layer around the earth. The main cause of the ozone hole was found to be gases that contained chlorofluorocarbons (CFCs), halons and freons. Found commonly in aerosol cans and released by many electronic appliances, these decrease the level of ozone in the stratosphere. All of these gases contain chlorine, which is a major cause behind the thinning of the ozone layer. The presence of chlorine within CFCs break down the ozone gases in ozone layer which increases the chances of ozone depletion. CFCs have accounted for about 80% of ozone depletion.