Ozone and the Ozone Hole Heather Raven & Stefanie Spayd

Background  Magnitude of polar O 3 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 O 3 loss)  Antarctic has larger polar vortex and colder temps than Arctic = more concerned with O 3 at the southern pole (greater O 3 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

 Catalyst to breaking up the ozone layer.  Breaks up O 3 into O 2 and O  Breaks up CFCs to produce Cl  Cl combines with Oxygen atoms, preventing them from combining with O 2 to form ozone.  Thus, creating a lack of ozone molecules in the atmosphere. Sunlight

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 Cl 2 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)  CO 2  H 2 O

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.