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University of Bristol
Wellcome Trust
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PEEP for Physics & Ethics at GCSE


CFC’s and the Ozone Layer

What is the ozone layer?

  • 90% of the world’s ozone (O3) is found in the high atmosphere (upper stratosphere – 17km to 26km above the earth’s surface). Mount Everest is 9km high.
  • This is a renewable thin veil which is essential for life as it protects against 99% of harmful U.V. radiation reaching the surface of the Earth.
  • Ozone is formed by the action of U.V. radiation on oxygen.
    O2 is split by U.V. radiation into O + O
    O2 then combines with O to form O3
  • At low levels (the troposphere – surface up to 15km) ozone can be harmful.
    • It acts as a super-greenhouse gas (105 worse than Carbon Dioxide)
    • Traps pollution (dust and smoke) causing city ‘smogs’.
    • Direct irritation to eyes and lungs.
    • Damage to leaves and may reduce crop production by 10%.
    • Ozone at low level is produced by fossil fuel combustion.
      NO2 is released by combustion
      NO2 is split by U.V. radiation into NO + O
      O2 then combines with O to form O3

Value of the upper ozone layer.

  • Stratospheric ozone absorbs solar ultraviolet radiation which would otherwise reach the Earth’s surface.
  • Some UV-B (290-320nm) reaches the earth and causes:
    • Sunburn
    • Some forms of cancer
    • Eye cataracts
  • UV-C (240-290nm) does not at present reach the surface but laboratory tests have shown that it causes damage to DNA (increased mutation rates) and proteins.


 Ozone Holes


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