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Ozone layer depletion:

Ozone (O3) occurs naturally in the atmosphere. It forms a layer which is denser towards the poles and thinnest in the tropics (around the equator). Ozone is formed in the atmosphere when ultraviolet radiation from the sun strikes the stratosphere splitting oxygen molecules (O2) into atomic oxygen (O). The atomic oxygen quickly combines with further molecules to form ozone.

O2 + hv → O + O                                  (1)

O + O2 → O3                                        (2)

Ozone is a pollutant in the troposphere because in the presence of sunlight it breaks into O2 and O and reacts with oxides of nitrogen and hydrocarbon which result in smog whereas in the stratosphere it absorbs the UV radiation of sun and protects the living organisms and hence a life saver in the stratosphere.

Although the UV radiation splits the ozone molecule, ozone can reform through following reactions resulting in no net loss of ozone

O3 + hv → O + O2                               (3)

O + O2 → O3                                        (4)

Ozone is destroyed by the following reaction with atomic oxygen

O + O3 → 2O2                                     (5)

The reactions 1-4 are known as the “Chapman reactions” and the layer of ozone formed in the stratosphere by these reactions is known as “Chapman Layer”.



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