A the upper stratosphere. Once those CFCs

A refrigerant is a substance that is normally a fluid, applied in the system of a refrigeration cycle. Throughout the refrigeration cycles, the refrigerant undergoes phase changes from a liquid to gas back and forth.The refrigeration systems back from earlier era used chemicals such as ammonia (NH3), sulfur dioxide (SO2) and methyl chloride (CH3Cl). However, ammonia, sulfur dioxide and methyl chloride are toxic in nature. In the year of 1920s, numerous lethal accidents were reported which was triggered by the leakage of methyl chloride from refrigerators. Following that incident, there had been a joint effort by scientists and researchers to develop a less hazardous refrigerants. The collaborative investigation of less dangerous refrigerants eventually led to the discovery and development of chlorofluorocarbons (CFCs) in the 1950s. CFCs are a class of compound consists of carbon, chlorine, hydrogen and fluorine. Because of its non – toxicity, inert and low flammability characteristics, CFCs rapidly replaced sulfur dioxide and methyl chloride and dominated the refrigerant market. However, in the year of 1974, Sherry Rowland and Mario Molina discovered the contribution of CFCs to ozone depletion in the upper stratosphere. The key finding from Sherry Rowland and Mario Molina was that the low reactivity of CFCs allowed CFCs to have a lifespan long enough to diffuse into the upper stratosphere. Once those CFCs compounds reach the stratosphere, ultraviolet (UV) radiation by the sun is powerful to trigger the homolytic cleavage of the C-Cl bond. The chlorine atom broken off from C – Cl bond reacts and removes an oxygen atom from an ozone molecule (O3) to form chlorine monoxide (ClO). The chemical product of the reaction are chlorine monoxide and oxygen. The ClO can then reaches out to react with another molecule of ozone, releasing the chlorine atom and yielding two molecules of oxygen in the process. Ultimately, the amount of ozone in the ozone layer was decreased and a phenomenon known as ozone hole was observed. The ozone layer absorbs ultraviolet light radiated by the sun, thus serve as a barrier to shield the mankind from the damage of excessive ultraviolet light. The thinning of ozone layer results into the increase of UV light radiation penetrates through the Earth’s stratospheric layer. The excessive exposure to UV radiation is said to have an adverse effect on human health. Such health issues are skin cancer, cataracts and sunburns.    

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