• Earth has a protective umbrella in the form of ‘Ozone Layer’, of  24 kilometer thickness in the stratosphere about 15 km away from the earth’s surface.
  • The concentration of ozone in the stratosphere ozone layer is about 10 ppm compared to 0.05 ppm (about 0.0000017%) in the troposphere.
  • Higher ozone concentration in the troposphere are highly injurious to man on earth.
  • The stratospheric ozone layer is essential for life to sustain on earth.
  • The Ozone layer observed dangerous ultraviolet radiation from the sun and converts it to heat and chemical energy. For this response it is rise in temperature.The Ozone layer is not of uniform thickness, its profile is shaped like that of Earth, being highest at the equator and lower at the poles.
  • In ozone is continuously formed and destroyed through photo chemical interaction and an equilibrium in ozone concentrations is ensured. This is equilibrium due to discharge of anthropogenic air pollution, such as Chlorofluorocarbons (CFC’s) into the atmosphere.
  • CFC’s released free radicals of chlorine, fluorine or bromine, which destroy the stratospheric ozone in which Ozone layer is thinned.
  • The patches of the thinned ozone layer are known as ‘Ozone Holes’.
  • The ‘Ozone Holes’ represents only a depletion of Ozone concentration, but not an empty space in the atmosphere.
  • The British Antarctic Survey Team (BAST) research revealed that the ozone level was dropped by 50% from August,15,1987 to October,7,1987 and the ozone dropped by 100% in some parts literally forming ‘Ozone Holes’.


  • Chloro Fluro Carbons are a group of synthetic chemicals developed in 1930 by Dr. Thomas Midgley.
  • The compound CCl₂F₂ marketed such as “Freon” and “Genetron”. The low toxicity, non inflammability and least chemical reactivity of CFC’s made them very popular in being used as refrigerants.
  • In 1940 ” DU Pont” developed a series of chlorofluorocarbons. Prior to CFC’s, ammonia and sulfur dioxide were used as refrigerants. They are highly corrosive and toxic hence it is used very much limited.
  • The use of CFC’s is of a wide range. Freon – 11, Freon – 12, Freon – 22, Freon – 113 and Freon – 114 are used in aerosols, aerosol propellants, cleaning foams, air conditioning, refrigeration and sterilization. Halon like CF₂BrCl are used in fire extinguishers.
  • The CFC’s in such clouds react with sunlight to form smog. This raises the temperature of the atmosphere and also causes the thinning of the ozone layer.
  • The main ozone depletion reactions are:
  • O₃ ——> O₂ + O
  • Cl + O₃ ——> ClO+O₂
  • CCl₃F(Freon) ——hv—–> CCl₂F+Cl
  • ClO+O₃ ——- h  ——> Cl + 2O₂
  • Every molecule of chlorine can destroy lakhs of molecules of ozone without itself being destroyed.
  • CFCs are the main pollutants responsible for Ozone depletion.

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