Layers of the Atmosphere
The atmosphere consists of five layers: The troposphere, the stratosphere, the mesosphere, the thermosphere, and the exosphere. The thickness of these layers is slightly different around the globe, and also varies according to temperature and season. In this discussion, we will focus primarily on the troposphere and the stratosphere because human-made pollutants affect the function of the lower layers.
Consequently, weather phenomena such as clouds, lightning, thunder, storms and rain take place in this layer.
Carbon dioxide is much heavier than the other gases. So the amount of carbon dioxide is higher in this lower layer of the atmosphere. It tends to decrease as the altitude increases. Therefore the temperature decreases with the increasing altitude at the rate of 1'C per 165 metres. This ratio of decrease in temperature with the increase of altitude is called the lapse rate.
Among the above said layers of the atmosphere, the stratosphere filters the ultraviolet rays and protects the Earth. Let us now learn the significance of ozone layer and its depletion.
In the troposphere, 'bad' ozone is an air pollutant . It damages human health and vegetation. It is a key ingredient of urban smog. In the stratosphere, we find the 'good' ozone that protects life on earth from the harmful effects of the sun's ultraviolet rays.
Ozone is constantly being formed in the earth's atmosphere by the action of the sun's ultraviolet radiation on oxygen molecules. Ultraviolet light splits the molecules apart by breaking the bonds between the atoms. A highly reactive free oxygen atom then collides with another oxygen molecule to form an ozone molecule. Because ozone is unstable, ultraviolet radiation quickly breaks it up, and he process begins again.
About 90% of the zone in the earth's atmosphere lies in the stratosphere. Ozone forms a very thin layer in the stratosphere, where it is more concentrated than anywhere else. While both oxygen and ozone together absorb 95 to 99.9% of the sun's ultraviolet radiation, only ozone effectively absorbs the most energetic ultraviolet light, which causes biological damage.
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