Upper part of the atmosphere is called the stratosphere.
Ozone is a layer in the earth’s stratosphere which acts as a shield absorbing ultraviolet radiation from the sun.
Fig. ozone layer
UV rays are highly injurious toliving organisms as the chemical bonds within DNA and proteins of living organisms break by its high energy.
The thickness of the ozone in a column of air from the ground to the top of the atmosphere is measured in terms of Dobson units (DU).
Ozone gas is continuously formed by the action of UV rays on molecular oxygen, and also degraded into molecular oxygen in the stratosphere so there should be a balance between production and degradation of ozone in the stratosphere.
The balance has been disrupted due to enhancement of ozone degradation by chlorofluorocarbons (CFCs).
CFCs discharged in the lower part of atmosphere move upward and reach stratosphere.
In stratosphere, UV rays act on them releasing Cl atoms.
Cl degrades ozone releasing molecular oxygen, with these atoms acting merely as catalysts.
Ozone depletion resulted in formation of a large area of thinned ozone layer, commonly called as the ozone hole.
UV-B damages DNA and mutation may occur which causes aging of skin, damage to skin cells and various types of skin cancers.
In human eye, cornea absorbs UV-B radiation, and a high dose of UV-B causes inflammation of cornea, called snow-blindness cataract.
An international treaty Montreal Protocol, was signed at Montreal (Canada) to control the emission of ozone depleting substances.