8. Our Environment
The amount of ozone in ozonosphere began to drop in 1980s. A spring time ozone hole (area of extreme thinness of ozone) was discovered over Antarctica in 1985 by Farman et al. Its area has been spreading subsequently. An ozone reduction of 1% increases the amount of high energy UV–B radiations reaching the earth by 2%. It means that there has been increase in UV–B radiations reaching the earth by 15–20%. ODS :
Ozone depleting substances or ODS are those substances which react with ozone present in the stratosphere and destroy the same. The main ozone depleting substances are chlorofluorocarbons (CFCs), halons, nitrous oxide, methane, carbon tetrachloride and chlorine. Chlorofluorocarbons are highly stable, odourless, synthetic gaseous substance used as aerosol propellants, coolants, refrigerants, blowing agents, etc.