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The Ozone hole – Dobson Units and CFC replacements

The Ozone hole – Dobson Units and CFC replacements. What is a Dobson Unit?. One Dobson units equals one-hundredth of a millimeter thickness of ozone layer at standard temperature and pressure (STP). Dobson Units. Ozone measured by Earth Probe TOMS over 43.00 Degrees Latitude

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The Ozone hole – Dobson Units and CFC replacements

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  1. The Ozone hole – Dobson Units and CFC replacements

  2. What is a Dobson Unit? • One Dobson units equals one-hundredth of a millimeter thickness of ozone layer at standard temperature and pressure (STP).

  3. Dobson Units • Ozone measured by Earth Probe TOMS over43.00 Degrees Latitude -74.00 Degrees Longitudeon 2004/09/16 is 275 Dobson Units

  4. http://toms.gsfc.nasa.gov/

  5. Why are there ozone holes above and below the poles? • Conditions • Cold • Light – dark periods (summer winter) • Swirling vortex of air

  6. Free radical sequestering • We left our discussion at the ‘sequestering’ of ClO. and Cl. ClO. + NO2 → ClONO2 Cl. + CH4 → HCl + CH3 Sequestered molecules can be “rained out when stratospheric and wet tropospheric air mix in the upper troposphere.” T.G Spiro and W.M. Stigliani

  7. Cold:Absorption on ice (solid surface) • However, the danger occurs when these can’t be rained out. Further danger occurs when solid surfaces are present. ClONO2 and HCl can be absorbed in ICE ClONO2 + HCl → Cl2 + HNO3 ClONO2 + H2O → HOCl + HNO3

  8. Light: Formation of Radicals From previous slide: ClONO2 + HCl → Cl2 + HNO3 ClONO2 + H2O → HOCl + HNO3 What happens to Cl2 in light and HOCl in light?

  9. Why are there ozone holes above and below the poles? • Conditions • Cold • Light – dark periods (summer winter) • Swirling vortex of air Ice formation Keeps ice crystals suspended in stratosphere Allows for accumulation of ClONO2

  10. CFC Substitutes and the ‘Protocols’ • Montreal protocol (1987) – 31 countries agree to cut CFC production by 50% by the year 2000 • London Protocol (1990) ban CFC production by 2000 • Helsinki and Copenhagen (1992) – ban CFC production by 1996.

  11. Ozone hole appears Ozone hole disappears

  12. F Cl H H C C F H C C F H F F H Cl Substitutes • HFC’s Blowing Agent Refrigerant Replaces CFC-11 Replaces CFC-12 95% less Damaging Than CFC11 HFC-134a HCFC-141b

  13. CFC Replacements • What substitutes did you find? • Refrigeration and Foaming agents

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