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Ozone depletion

Ultra-Violet Radiation (U.V.): wavelength less than 0.4 μ m. 1.2% of the Sun's radiant energy occurs at  <0.3 μ m. U.V. with  <0.3 μ m (photon energy>4eV) is strongly ionising. Can lead to skin cancers, cataracts, etc. It can harm corps and disrupts aquatic ecosystems.

rashad-joyner
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Ozone depletion

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  1. Ultra-Violet Radiation (U.V.): wavelength less than 0.4μm. 1.2% of the Sun's radiant energy occurs at  <0.3μm. U.V. with  <0.3 μm (photon energy>4eV) is strongly ionising. Can lead to skin cancers, cataracts, etc. It can harm corps and disrupts aquatic ecosystems. The Ozone Layer is the peak in O3 concentration that occurs in the stratosphere. O3 absorbs almost all U.V. with  <0.290μm. hn + O2 O + O ; O + O2 O3 ; hn + O3 O2 + O  O3 The above occurs many times until some interference reaction removes either or both the O3 and O species. Ozone depletion

  2. Used as coolants, propellants, solvents, etc Very unreactive. Half-live 70- 200 years in the troposphere. Diffuse into the stratosphere where they are dissociated by U.V. releasing free Cl atoms. Cl atoms remove O3 and O in the catalytic chlorine cycle Cl + O3 O2 + ClO ClO + O  Cl + O2 RESULT Cl + O3 + O  Cl + 2O2 Each chlorine atom can destroy about 105 O3 molecules. Chloroflurocarbons (CFCs)

  3. Interference reactions e.g. Cl O + NO2 ClONO2 and H + Cl  HCl  rapidly remove the Cl. Experiment and calculation show that such reactions should keep the Cl in check. So CFCs should have little impact on the ozone layer. Interference Reactions

  4. British Antarctic Survey Have carefully monitored ozone levels above Antarctica for last 50 year

  5. First reported in 1985. In the Antarctic spring up to 80% of the ozone is lost. In December (Mid Summer) the Antarctic U.V. level is about 3 times normal. In late spring the low O3 air moves out from Antarctica leading to record low levels of O3 over southern Australia and New Zealand. Antarctic Ozone Hole

  6. In winter air gets trapped over the Antarctic in the Polar Vortex. In the extreme cold Polar Stratospheric ice clouds form which trap the NO2. The reaction HCl + ClONO2 Cl2 + HNO3 can occur efficiently on the crystals surfaces. Thus the interference reactions are stopped and the Cl is released as soon as the temperature rises slightly in spring. Polar VortexPolar Stratospheric Clouds

  7. Extent of the Ozone hole

  8. Sulphuric acid crystals, which are found throughout the stratosphere, can act in a similar way to PSCs. The 1990 Pinatubo volcanic eruption put very large quantities of aerosol material including H2SO4 crystals into the stratosphere. This led to strong reductions in ozone levels at more northerly latitudes including northern Europe. The Global implications

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