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The Ozone hole Dobson Units and CFC replacements
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What is a Dobson Unit?

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

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Dobson Units

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

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http//toms.gsfc.nasa.gov/
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(No Transcript)
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Why are there ozone holes above and below the
poles?

• Conditions
• Cold
• Light dark periods (summer winter)
• Swirling vortex of air

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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

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ColdAbsorption on ice (solid surface)

• However, the danger occurs when these cant 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

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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?

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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
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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.

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Ozone hole appears
Ozone hole disappears
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Substitutes

• HFCs

Blowing Agent
Refrigerant
Replaces CFC-11
Replaces CFC-12
95 less Damaging Than CFC11
HFC-134a

• HCFC-141b

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CFC Replacements

• What substitutes did you find?
• Refrigeration and Foaming agents