7.75 - Ozone Depletion
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7.75 - Ozone Depletion Presentation Transcript

  • 1. Ozone Depletion
    • You should know and understand;
    • What is ozone, where does it occur and why is it important?
    • The difference between good and bad ozone
    • How human pollutants affect levels of stratospheric ozone leading to ozone depletion and the “ozone hole”
    • The impact of ozone depletion on plants and animals
    • How international treaties have addressed the ozone issue
  • 2. What is ozone, where does it occur and why is it important?
    • Ozone is trioxygen (O 3 )
    • Ozone is found in both the troposphere (lower atmosphere) and the stratosphere
    • In the stratosphere the ozone forms a “layer”, this layer is important as it protects us from UV radiation – ozone is responsible for filtering a very high percentage of UV radiation
  • 3. The difference between good and bad ozone
    • The ozone is the stratosphere is GOOD ozone as it filters the UV radiation
    • Ground level tropospheric ozone is BAD ozone as it can exacerbate asthma and cause other respiratory and associated health problems
    • When you investigate urban microclimates and pollution you will study ground level ozone
  • 4. Ozone Depletion
    • Ozone is continually created and destroyed within the stratosphere (O+O 2 =O 3 +O=2O 2 +O=O 3 etc.)
    • The total amount of ozone in the stratosphere is determined by the balance between photochemical production and recombination
    • This good ozone in the stratosphere can be destroyed by ozone depleting substances (ODS)
    • ODS include chlorofluorocarbons (CFCs), hydro-chlorofluorocarbons (HCFCs) and halons – these have anthropogenic sources such as coolants in air conditioning systems and propellants in aerosol sprays.
    • Whilst the source of much of the worlds ODS has been removed (see Montreal Protocol below) it is worth remembering that 1 chlorine atom can destroy 100,000 molecules of ozone and these chlorine atoms stay in the stratosphere a long time.
  • 5. The Ozone Hole
    • Whilst CFCs and other ODS led to a depleltion in global stratospheric ozone levels this was not distributed evenly.
    • In the tropics no noticeable declines have been recorded, whilst in middle latitudes declines of between 3 and 6% have been measured.
    • Reactions that take place in polar stratospheric clouds speed up the depletion of ozone – thus levels of depletion of Antarctica (where such clouds are common) were much faster than elsewhere.
    • This is where the concept of an “ozone hole” first emegred
  • 6. Ozone depletion over Antartica
  • 7. The largest Antarctic ozone hole ever recorded (Sept 2006)
  • 8. The Impacts of Ozone Depletion
    • Less ozone = more UV penetration into the troposphere and lower atmosphere
    • The most serious human impacts are skin cancer and cataracts
    • Increased tropospheric UV radiation can lead to greater levels of BAD tropospheric ozone
    • High levels of UV can also affect rice and plankton growth
  • 9. 1989 Montreal Protocol
    • This is a good example of a successful international treaty to tackle a climatic hazard issue
    • It has undergone 7 revisions since it was first ratified in 1989
    • Levels of CFCs and other ODS have declined
    • Even with these success it will be 2050 before the ozone layer will have fully recovered