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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.

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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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