Ozone layer (Importance, depletion, effects and protection of ozone layer)

  • Ozone is a pale-blue gas that forms a layer in the stratosphere of our atmosphere called ozone layer.
  • This layer absorbs about 99% harmful solar radiations like UV rays, X rays, gamma rays etc. and protects living organisms from harmful ultraviolet radiation as well as helps to maintain the temperature of the earth.
  • Ozone layer is the protective layer present in our atmosphere.
  • Ozone formation is a natural process, which is formed by the combination of three oxygen atoms due to the influence of UV radiation.
  • When an oxygen molecule absorbs high energy solar radiation, it dissociates into nascent oxygen [O] which is highly reactive and thus it combines with oxygen molecule and forms a molecule of ozone.

Importance of ozone layer:

  • The ozone layer protects the earth from the harmful UV radiations.
  • It not only absorbs UV radiations but also the radiations of wavelength less than 3×10-7
  • It prevents us from dangerous diseases like cataracts (blindness), skin burns, skin cancer and weak immune system due to over exposure of UV radiations.
  • It also helps balance weather and temperature of the earth and to maintain greenhouse effect.

Depletion of ozone layer:

  • The decrease in the thickness of the ozone layer of formation of hole in it is called ozone depletion.
  • According to environmental scientists, the CFCs (chlorofluorocarbons) and oxides of nitrogen, when released from lower atmosphere reach the stratosphere and destroy the ozone layer.
  • CFC is a stable non-toxic, non-inflammable and cheaply produced chemical which is released by aerosol spray cans, refrigerators, air conditioners, industries, research laboratories etc.
  • When this CFC reaches the stratosphere, it undergoes photolytic dissociation due to influence of ultraviolet radiation, as a result of which, nascent chlorine is released and converts ozone to oxygen, which takes place as follows:
    • CFCl3 —-> CFCl2 + Cl (free chlorine)
    • Cl + O3 —-> O2 + ClO
    • 2ClO —-> 2Cl + O2
  • CFC is a major industrial chemical that depletes ozone layer. It is cheaper than ammonia and is used as a refrigerant.
  • Along with CFCs, methyl chloroform, methyl bromide, carbon tetrachloride etc. are also responsible for ozone layer depletion.
  • Similarly, oxides of nitrogen like nitric oxide (NO), nitrogen dioxide (NO2) etc. which is liberated by airplanes, rockets and chemical fertilizers react with ozone and convert it into oxygen. Hence, oxides of nitrogen also deplete ozone layer as follows:
    • NO + O3 —-> NO2 + O2
    • 2NO + O3 —-> N2O3 + 2O2
  • The extremely cold temperature, i.e. -85oC to -90oC in Antarctica plays a significant role in ozone layer depletion.
  • Ozone and chlorine containing molecules are absorbed on the surface of ice crystals at high altitudes in Antarctica and in the presence of solar radiation, chlorine ions are liberated that react with ozone and form oxygen gas.

Effects of ozone layer depletion:

  • The depletion of ozone layer affects physical as well as biological aspects of the earth.
  • In human beings, UV rays cause serious diseases like cataract, skin burns, eye burns, skin cancer, leukemia etc also weakens our immune system.
  • Over exposure to UV rays may lead to mutation (due to formation of thymine dimer in DNA) in different organisms.
  • Over exposure to UV rays also hampers the growth and development of plants and animals.
  • Due to ozone layer depletion, more solar radiation enters the earth’s surface which increases the temperature of the earth and causes global warming.
  • UV rays reduce the rate of photosynthesis and crop production in plants.
  • Due to more heat, various species of plants and animals may go extinct and also brings about significant changes in climatic conditions.

Protection of ozone layer:

  • Ozone layer can be protected by reducing the production of CFC and oxides of nitrogen or completely putting a ban on their production.
  • Alternative chemicals should be used in refrigerators, air conditioners and other machines instead of CFCs.
  • Public awareness should be generated about the importance of ozone layer, harmful effects from its depletion and its protection.

Ozone layer (Importance, depletion, effects and protection of ozone layer)