The ozone hole in the Earth's atmosphere Ozone is a gas composed of ozone molecules which consist of three atoms of oxygen (O 3 ). Many studies has discovered that in every 10 million molecules in the stratosphere up from the earth's surface to about 10-50 km, only 3 molecules of ozone are found. The stratospheric o zone absorbs every radiation from the sun, especially UV-B which is harmful to many lives and also interrupts the equilibrium of nature. Exposure to radiation, human eyes can be damaged, as found from studies that a 1% decrease of stratospheric ozone causes a 0.6-0.8% increase in eye cataracts. Besides, this UV-B radiation is also known to cause skin cancers, among of which is Coetaneous Malignant Melanoma mostly found on white people, and weaken human immune system causing much easier infection on human beings. Further to human impact, animal and plants are also adversely affected. In particular to aquatic organisms, UV-B interrupts the first phase of their evolvement by decreasing populations of planktons which are the base of most marine food chains. The ultraviolet radiation causes changes in the chemical composition of several species of plants and synthetic materials i.e. plastics rubbers as well as other natural materials including woods. These negative impacts heighten the importance of ozone which acts as the shelter preventing any harmful radiation from every life on earth. In 1978, Scientists who had been observing the concentration of gases in the atmosphere found that the density of ozone was continually decreasing. Seven years later, English explorers also found a 50-95% declination of ozone concentration in spring over Antarctica . This phenomenon was then called by the scientists as “Antarctic Ozone Hole”. Since the finding, the awareness had been widely spreaded and series of attempt had been dedicated to seek the cause of ozone depletion. The decrease of ozone concentration was found to have a relation with the increase of chlorine oxide. The studies of origin of chlorine in the atmosphere came out with reliable proofs that the increasing chlorine in the stratosphere was occurred from Halocarbons categorized chemicals including chlorine, fluorine, bromine, carbon and hydrogen, all of which are then called Ozone Depleting Substances (ODSs). The most widely known ODS is Chlorofluorocarbons or CFCs which are synthesized to be a variety of useful products, for instance, refrigerant in refrigerators and air conditioners, foam blowing agent in foam industry, solvent in electronic industry and aerosol propellant in canned spray etc. Due to positive characteristics of CFCs, namely hardly dissolve and toxic, cheap and easy to maintain, the uses of these chemicals had been quickly spreaded over and doubled in every 5 years since 1970. The main chemicals of CFCs are CFC-11, CFC-12, CFC-113, CFC-114 and CFC-115. Apart from CFCs, Halon, Carbon tetrachloride, Methyl chloroform, Methyl Bromide, and Hydro chlorofluorocarbons (HCFCs) are also found as ozone depleting substances, but their depletion potentials are less than CFCs. Like CFCs, these chemicals are hardly dissolved. They destroy ozone by drifting up to the stratosphere layer and breaking down into chlorine radicals when touching the solar radiation. The chlorine radicals set off chain reactions with ozone molecules, resulting in the decrease of the ozone concentration and eventually the ozone hole.
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