The ozone hole and its causes

HYPERLINK http//en.wikipedia.org/wiki/FileUars_ozone_waves.jpg HYPERLINK http//en.wikipedia.org/wiki/FileUars_ozone_waves.jpg o Enlarge Ozone hole in North America during 1984 (abnormally warm reducing ozone depletion) and 1997 (abnormally cold resulting in increased seasonal depletion). Source NASA HYPERLINK http//en.wikipedia.org/wiki/Ozone_depletion l cite_note-13 14 The Antarctic ozone hole is an area of the Antarctic stratosphere in which the recent ozone levels have dropped to as low as 33 of their pre-1975 values. The ozone hole occurs during the Antarctic spring, from September to early December, as strong westerly winds start to circulate around the continent and create an atmospheric container. Within this HYPERLINK http//en.wikipedia.org/wiki/Polar_vortex o Polar vortex polar vortex, over 50 of the lower stratospheric ozone is destroyed during the Antarctic spring. HYPERLINK http//en.wikipedia.org/wiki/Ozone_depletion l cite_note-14 15 As explained above, the primary cause of ozone depletion is the presence of chlorine-containing source gases (primarily CFCs and related halocarbons). In the presence of UV light, these gases dissociate, releasing chlorine atoms, which then go on to catalyze ozone destruction. The Cl-catalyzed ozone depletion can take place in the gas phase, but it is dramatically enhanced in the presence of HYPERLINK http//en.wikipedia.org/wiki/Polar_stratospheric_cloud o Polar stratospheric cloud polar stratospheric clouds(PSCs). HYPERLINK http//en.wikipedia.org/wiki/Ozone_depletion l cite_note-15 16 The HYPERLINK http//en.wikipedia.org/wiki/Photochemistry o Photochemistry photochemicalprocesses involved are complex but well understood. The key observation is that, ordinarily, most of the chlorine in the stratosphere resides in stable reservoir compounds, primarily hydrochloric acid (HCl) and chlorine nitrate (ClONO2). During the Antarctic winter and spring, however, reactions on the surface of the polar stratospheric cloud particles