OZONE

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OZONE OZONE LOSS
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Ozone (O3)

• Discussed previously.
• Highly reactive air pollutant in lower
  troposphere.
• Valuable UV screen in stratosphere.

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Ozone (O3)

• How Ozone blocks UV
• O2 UV ? 2 O atoms
• O O2 ? O3
• O3 UV ? O O2 ? O3 , etc.

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Ozone (O3)

• Concentration in ozone layer decreasing, more UV
  reaching ground.
• ozone thinning
• Reason Chlorofluorocarbons
• CCl3F
• CCl2F2

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Ozone Thinning

• How CFCs degrade ozone
• CCl3F UV ? CCl2F Cl atom
• Cl atom O3 ? ClO O2
• ClO O atom ? O2 Cl atom
• etc.
• ClO and Cl atom slow to clear from stratosphere

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Ozone Thinning
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Ozone Thinning

• Other ozone damaging chemicals
• Halons
• Methyl bromide
• Carbon tetrachloride
• Trichloroethane ( methylchloroform)
• Hydrogen chloride ( HCl, hydrochloric acid)

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Ozone Thinning over Poles

• Atmospheric ice crystals with Cl2O2,
• Release of Cl atoms in polar spring,
• Effect first noticed, measured over Antarctica
  later over Arctic.
• Effects on nearby regions,
• Australia
• Southern Africa

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Ozone Thinning and UV

• Effects of UV radiation at Earth surface
• Sunburn
• Cataracts in eye lenses
• Skin cancers
• Skin is largest organ of human body.

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Ozone Thinning and UV

• Skin cancers
• Basal cell carcinoma
• Squamous cell carcinoma
• Melanoma

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Effects of UV radiation

• On animals plants
• Cataracts, blindness
• Leaf damage, reduced photosynthesis
• Damage to bacteria, fungi on soil surface, etc.
• On commercial materials
• Fading of paints
• Damage to plastics

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Effects of UV radiation

• Montreal Protocol, 1987
• Copenhagen Protocol, 1992
• Both encourage reductions of CFC production use
  ( of other ozone destroying chemicals)
• Methyl bromide still widely used as fumigant in
  stored grain.
• CFC production in industrialized countries down
  80 since 1989
• Stratospheric ozone expected to regain 1980
  concentration about 2050
• Assumes no further releases of ODCs