Tag: commercial applications

The region of stratosphere, at an altitude of 16-50km over equator and at a slightly lower altitude elsewhere having a thick sheet of ozone is known as ozonosphere. Decline in the thickness of ozone layer over a restricted area is called ozone hole. It was first discovered over Antarctica in 1985 by Dr. Joe C. Farman and his colleagues in the British Antarctica surveys. Chlorofluorocarbons are mainly responsible for ozone depletion in the stratosphere. CFC's are used as coolants in refrigerators and air conditioners, as propellants, cleaning solvents. Once released into the atmosphere, CFC'S reach the stratosphere and produce active chlorine in the presence of UV radiations. These radicals through chain reaction destroy ozone by converting it into oxygen.

Ozone layer is a region of concentration of ozone molecule. $O _3 (O _2+ O)$ in the earth's atmosphere. The layer lies in the stratosphere at an altitude of 18-50 kms. The ozone layer naturally Shields earth's life from the harmful effect of the Sun's ultraviolet radiations. A severe depletion of ozone (ozone hole) in a region of the ozone layer was found particularly over Antarctica.  The depletion is caused by chlorofluorocarbons and by other compounds like $CCI _4, CF _4$ etc. So, the correct answer is 'Thinning of the ozone layer'.

We know that surrounding the troposphere of earth, there is a layer of the stratosphere. It is made up of ozone molecules that are formed by the effect of UV rays in these areas. Due to excessive chlorofluorocarbon compounds, and emission of carbon dioxide, it is getting depleted. At the poles, it is constantly getting thinner and thinner. This is called the ozone hole. 

Depletion of ozone layer is noticed all over the earth.
Ozone is destroyed by collisions with other atoms and molecules.

• 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.