OZONE DEPLETION AND THEIR EFFECT
The Ozone is found in the upper part of the atmosphere called the stratosphere, and it acts as a shield absorbing ultra violet from the Sun.
UV rays a are highly injurious to living organisms since DNA and PROTEINS of living organisms preferentially absorb UV rays, and it’s high energy breaks the chemical bond within these molecules.
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.There should be a balance between production and degradation of ozone in the stratosphere. Of late , the balance has been disrupted due to enhancement of ozone degradation by chlorofluoroarbons ( CFCs ).
CFCs fined by use as refrigerants.
CFCs discharged in the lower part of atmospher move upward and reach stratosphere. In stratosphere, UV rays act on them realising C1 atoms. C1 degrades ozone realising molecular oxygen , with thise atoms acting merely as catalysts ; C1 atoms are not consumed in the reaction.
Hence, whatever CFCs are added to the stratosphere,they have permanent and continuing affects on Ozone levels. Although ozone depletion is occurring widely in the stratosphere, The depletion is particularly marked over the Antarctic region. This has resulted in formation of a large area of thinned ozone layer, commonly called as the ozone hloe.
UV radiation of wavelengths shorter than UV- B, are all most completely absorbed by Earth’s atmosphere, given that the ozone layer intact. But , UV- B damages DNA and mutation may occur. It causes aging of skin,damge to skin cells and version type 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 and cataract etc. Such exposure may permanently damage of cornea. Recognition the deleterious affect of ozone depletion, an international traety , known as the Montreal Protocol, was signed at Montreal in 1987 to control the emission of ozone depleting substance.
The development of the fertile top soil takes centuries . But it can be removed very easily due to human activity like over cultivation, unrestricted grazing , deforestation and poor irrigation practices, resulting in arid patches of land. When large barren patches extended and meet over time , a desert is created. Internationally , it has been recognised that desertification is a measure problem nowadays, particularly due to increased urbanization.
Irrigation without proper drainage of water leads to waterlogging in the soil. Besides effecting the crops , waterlogging draws salt to the surface of the soli. The salt then is deposited as a thin crust on the land surface or starts collection at the roots of the plants. These increased salt content is inimical to the growth of crops and is extremely damaging to agriculture .