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The ozone hole

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O. O. O. © NOAA. The ozone hole. © 2007 Paul Billiet ODWS. Ultra Violet light. © 2007 Paul Billiet ODWS. UV light and life. UV light is high energy light When it strikes molecules it can cause them to beak into ions or free radicals

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The ozone hole

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  1. O O O © NOAA The ozone hole © 2007 Paul Billiet ODWS

  2. Ultra Violet light © 2007 Paul Billiet ODWS

  3. UV light and life • UV light is high energy light • When it strikes molecules it can cause them to beak into ions or free radicals • The free radicals in turn damage large molecules such as proteins and DNA • Damage to DNA causes mutations • It is a mutagen • Mutations can lead to cancer © 2007 Paul Billiet ODWS

  4. UV light and life • UV light can have beneficial effects too • It stimulates the transformation dietary steroids into Vit D (calciferol) • UV light is used to sterilise foods and medical equipment • Some animals can see UV light • Insects use it to guide them to nectar sources in flowers © 2007 Paul Billiet ODWS

  5. ACGCTGGCTTAGT TGCGACCGAATGA ACGCTGGCT=TAGT TGCGACCGAATGA UV light & DNA • UV-B has a direct effect on DNA • DNA absorbs UV light of 260nm • The action of UV forms thymine dimers • This can cause a gene mutation when the DNA replicates UV-B Thymine dimer DNA © 2007 Paul Billiet ODWS

  6. Specific damage by UV light • Sunburn • Clouding of the cornea and formation of cataract • Skin cancer (melanoma) • Reduced rates of photosynthesis © 2007 Paul Billiet ODWS

  7. Ozone in the atmosphere • Ozone (O3) forms under the effect of UV light in the stratosphere • Ozone can also form in the troposphere • Naturally it forms from volcanic activity • It is produced by motor vehicules so it is a pollutant • Sunlight acts on NOx to produce O3 © 2007 Paul Billiet ODWS

  8. © Airparif Ozone pollution in the troposphere Safety limit

  9. The ozone layer • Ozone is an unstable gas • It rapidly breaks down • The ozone layer is only a few cm thick • If the rate of breakdown is faster than the rate of formation the ozone layer thins • This could develop into hole • An ozone hole was first observed over the Antarctic in 1985 © 2007 Paul Billiet ODWS

  10. The cause of the hole • Chlorofluorocarbons (CFCs) • The breakdown under the effect of UV light to release chlorine radicals (Cl) • Especially under cold conditions • The chlorine radicals react with O3 converting it to O2 and more radicals ClO © 2007 Paul Billiet ODWS

  11. What are CFCs? • Used as propellants in aerosol spray cans • Used as refrigerants in fridges, freezers and air conditioning units © 2007 Paul Billiet ODWS

  12. What can be done? • Reduce the use of CFCs • They are already banned in aerosols (1987) • BUT they are still used as refrigerants • Recycle fridges and air conditioning plants © 2007 Paul Billiet ODWS

  13. The current situation • The holes developing over the pole suggest that they may be show an improvement • BUT CFC molecules take 30 years to rise up to the stratosphere • The chlorine radicals last a long time • The peak ozone damage was supposed to be in 2000 • Damage could go on another 50 years © 2007 Paul Billiet ODWS

  14. © NASA The biggest yet September 2006

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