Ozone and the Ozone Hole

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Ozone and the Ozone Hole
Heather Raven Stefanie Spayd
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Background

• Magnitude of polar O3 loss depends on chlorine
  activation which is controlled by polar
  stratospheric clouds that depend on temperature
  (Tilmes et al., 2006)
• What are the important factors?
• Sunlight, Greenhouse Gases, and Temperature
• The Arctic also has an ozone hole, but has
  greater total column ozone than in the Antarctic
  because of dynamical re-supply of ozone (less O3
  loss)
• Antarctic has larger polar vortex and colder
  temps than Arctic more concerned with O3 at the
  southern pole (greater O3 loss)
• New studies predict that no statistically
  significant change in ozone hole decrease will
  occur until about 2024 (Newman et al., 2006)
• Full recovery sometime between 2053 and 2084

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Sunlight

• Catalyst to breaking up the ozone layer.
• Breaks up O3 into O2 and O
• Breaks up CFCs to produce Cl
• Cl combines with Oxygen atoms, preventing them
  from combining with O2 to form ozone.
• Thus, creating a lack of ozone molecules in the
  atmosphere.

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Greenhouse Gases and Ozone Hole

• Greenhouse gases warm the troposphere and cool
  the stratosphere.
• Polar stratospheric clouds (PSCs) contain
  molecules with chlorine, when the molecules react
  they form Cl2 after which sunlight splits the
  molecule into Cl Cl.
• PSCs form only in very cold stratosphere.
• Global warming is effectively enhancing ozone
  depletion!
• Stopping emission of GHGs now does not get rid of
  them right away
• Important to note that CFCs have remained in
  atmosphere even after emission ceased due to
  Montreal Protocol (lifetime 65 400 years)
• The main players
• Chlorofluorohydrocarbons (CFCs)
• CO2
• H2O

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Temperature and Ozone

• Climate Change Changing Temperature in the
  Stratosphere
• GHG ? Temperature ? Ozone hole duration ? (In
  Antarctic)
• Cooling of lower-stratosphere contributes to
  ozone loss
• Chlorine activation below 195 K temps in
  stratosphere
• 195 K is threshold for formation of PSCs
• Antarctic below this threshold much of winter
  season
• Arctic below this threshold less in winter
  season, less ozone loss from chlorine

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Take Home Points

• Continued anthropogenic release of greenhouse
  gases, not only CFCs, into the atmosphere will
  enlarge the ozone holes, letting more harmful UV
  rays reach the Earths surface.
• Temperature of the stratosphere is a key factor,
  as is sunlight, in the depletion of ozone.
• These processes are all intimately connected
  through chemical, radiative, and dynamical
  feedbacks.