Notes On Air Pollution: Stratospheric Pollution - CBSE Class 11 Chemistry
The tanning and burning of the skin are the effects observed normally. However, these are the least harmful, because sunrays can also cause skin cancer and cataract. Sunrays contain ultra violet or UV radiations. The top-most layer of our atmosphere, called the upper stratospheric layer, contains ozone, which is produced when the ultra violet radiations strike the dioxygen molecules from the earth's atmosphere. The UV rays split a dioxygen molecule into a free oxygen atom. This oxygen atom then combines with another oxygen molecule from the atmosphere to form an ozone molecule. The ozone so created forms a thin layer surrounding the earth. It protects animals and plants from the harmful UV radiations by acting as an umbrella that absorbs most of the UV rays and allows a very little of it to reach the earth. Although oxygen is photolysed into ozone every day, it is observed that the ozone layer has been depleting rapidly over certain areas due to the increasing presence of chlorofluorocarbons or freons in the stratosphere. These compounds are non-reactive, non-inflammable and non-toxic organic compounds that are constantly being generated to be used in refrigerators, air conditioners and electronic industries…etc. When these compounds reach the stratosphere hit by the UV radiations split releases free chlorine radicals and reacts with the ozone and form chlorine monoxide radicals and oxygen. Cl(g) + O3(g) → ClO(g) + O2(g) The chlorine monoxide radicals release even more chlorine radicals while reacting with oxygen, causes depletion of ozone layer. In Antarctica, ozone depletion reactions occur in spring as it requires the presence of sunlight. During the dark days of the winter, the region gets covered with stratospheric clouds. Ozone has depleted completely from a large area over the southern hemisphere, forming a hole in the ozone layer, called the ozone hole. The increasing use of fossil fuels and electronic goods has led to increasing pollution has thinned down the ozone layer over many places at an alarming rate. As a result, more UV radiations are entering the troposphere causing aging, sunburn, skin cancer and cataract in most animals, besides damage to reproductive functions in some fish. In plants, UV radiations cause mutation of cells by affecting plant proteins, increase the evaporation of surface water through the stomata of the leaves, kill phytoplanktons. UV radiation also decreases the moisture content of soil and fades paints and fibre, causing huge economic losses. Therefore reduce stratospheric pollution by reducing the use of chlorofluorocarbons, nitrogen dioxides and methane-releasing compounds.

#### Summary

The tanning and burning of the skin are the effects observed normally. However, these are the least harmful, because sunrays can also cause skin cancer and cataract. Sunrays contain ultra violet or UV radiations. The top-most layer of our atmosphere, called the upper stratospheric layer, contains ozone, which is produced when the ultra violet radiations strike the dioxygen molecules from the earth's atmosphere. The UV rays split a dioxygen molecule into a free oxygen atom. This oxygen atom then combines with another oxygen molecule from the atmosphere to form an ozone molecule. The ozone so created forms a thin layer surrounding the earth. It protects animals and plants from the harmful UV radiations by acting as an umbrella that absorbs most of the UV rays and allows a very little of it to reach the earth. Although oxygen is photolysed into ozone every day, it is observed that the ozone layer has been depleting rapidly over certain areas due to the increasing presence of chlorofluorocarbons or freons in the stratosphere. These compounds are non-reactive, non-inflammable and non-toxic organic compounds that are constantly being generated to be used in refrigerators, air conditioners and electronic industries…etc. When these compounds reach the stratosphere hit by the UV radiations split releases free chlorine radicals and reacts with the ozone and form chlorine monoxide radicals and oxygen. Cl(g) + O3(g) → ClO(g) + O2(g) The chlorine monoxide radicals release even more chlorine radicals while reacting with oxygen, causes depletion of ozone layer. In Antarctica, ozone depletion reactions occur in spring as it requires the presence of sunlight. During the dark days of the winter, the region gets covered with stratospheric clouds. Ozone has depleted completely from a large area over the southern hemisphere, forming a hole in the ozone layer, called the ozone hole. The increasing use of fossil fuels and electronic goods has led to increasing pollution has thinned down the ozone layer over many places at an alarming rate. As a result, more UV radiations are entering the troposphere causing aging, sunburn, skin cancer and cataract in most animals, besides damage to reproductive functions in some fish. In plants, UV radiations cause mutation of cells by affecting plant proteins, increase the evaporation of surface water through the stomata of the leaves, kill phytoplanktons. UV radiation also decreases the moisture content of soil and fades paints and fibre, causing huge economic losses. Therefore reduce stratospheric pollution by reducing the use of chlorofluorocarbons, nitrogen dioxides and methane-releasing compounds.

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