As we know that at around 23 kilometres from the surface of the earth there is a thick layer of ozone gas. It is formed by the action of sun’s rays on oxygen. The thicker layer of ozone also called ozone blanket is very effective in absorbing ultra-violet radiations given out by the sun. Thus, it produces the earth from the harmful effects of ultra-violet rays. Recently, in the year 1980 scientists have noticed a ‘hole in the ozone blanket covering the upper atmosphere around Antarctica. This fact is of great concern as harmful ultra-violet rays can now come to the earth though this hole. This wills the level of ultra-violet rays reaching the earth. An increased level of ultra-violet rays is very harmful as it can skin cancer and genetic disorders.
One of the causes of depletion of ozone layer is chlorofluorocarbons (CFCs). Another cause of depletion of ozone layer is emissions from jet aeroplanes. Chlorofluorocarbons have the largest ozone depletion potential (ODP). Chlorofluorocarbons when released from air conditioners, refrigerators, spray can sand industrial solvents drift in the stratosphere very slowly. Therefore each chlorine atom from chlorofluorocarbons gets sufficient time to destroy a large number of ozone molecules (approx. 100,000). The first chlorofluorocarbons produced in 1931 are still in the sky today. Now all over the world, the use of chlorofluorocarbons is being banned.
The currently available substitutes of chlorofluorocarbons are hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs). HCFCs contain one chlorine atom less than CFCs and are less harmful than CFCs. HFCs have no chlorine and hence ozone friendly. So the ideal solution seems to be to use HFCs. But all the three gases are green-house gases and have global warming potential.