A slight thinning of ozone layer occurs naturally for a few months every year over Antarctica. It decreases by \(67 ~\%\) every year. The primary chemicals responsible for ozone depletion are a group of chlorine containing compounds called chloroflurocarbons (CFCs), used as coolants in air conditioners and refrigerators (freon) and propellants for aerosol cans and form blowing agents for insulation and packaging and also as solvents. Besides halons, methyl bromide, methyl chloroform, carbon tetrachloride and nitrous oxide are also responsible for \(\mathrm{O}_3\) loss. After their release into troposphere, CFCs and other chlorine containing compounds go to stratosphere where these are broken down by UV-radiations releasing chlorine. Similarly bromine is released by breakdown of halons and methyl bromide. The sunlight catalyzes the chemical reaction by which chlorine or bromine break \(\mathrm{O}_3\) molecules and convert them into \(\mathrm{O}_2\) molecules. This chemical reaction does not change chlorine or bromine and thus single chlorine or bromine atom can breakdown many thousands of \(\mathrm{O}_3\) molecules.