Ozone

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Ozone and the Ozone Hole
Heather Raven & Stefanie Spayd
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
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.
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
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
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
Earth’s 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.
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