Ozone Depletion

(i) Ozone layer is present in stratosphere at altitude of 23-25 km (conc. 0.3 ppm) and act as shield against UV radiation.

(ii) Large hole has appeared in ozone shield over Antarctica and smaller one over North pole. (Discovered by Farman 1985).

(iii) Ozone is commonly called as chemical weed, 'Bad' ozone is formed in troposphere that harms plants and animals. Good ozone is found in stratosphere as shield.

(iv) ODS: ozone depleting substances -CFC, CH4, CCl4, halons and N2O causes destruction of O3.

(v) CFC's are most damaging. They release Cl free radicals in stratosphere which destroy O3.

(vi) Thinning of the ozone-layer results in an increase in the UV-B radiation.

(vii) UV -B damages DNA and mutation may occur. It causes aging of skin, damage to skin cells and various types of skin cancers. A high dose of UV-B causes inflammation of cornea called snow blindness.

(viii) Nowadays CFC's are being replaced by Hydro Fluoro Carbons (HFCs).