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If you thought that limitations on CFC production and usage would solve the ozone "hole" problem, unfortunately you were mistaken. A number of factors play a role. First, as noted in prior posts, some of the replacement chemicals turn out to not be ozone neutral, one might say, but attack ozone in a manner akin to CFC's. Second, a lot of CFC piracy is still going on. It is produced, used, and released into the atmosphere in many parts of the world. Third, as shown by this year's events, temperatures and weather patterns can exaccerbate the problem.
The spring thinning of Arctic ozone commences in February and has been far less severe than the hole that begins developing over the Antarctic each October, owing to a host of factors that affect ground-level weather in and around the poles. This year, however, conditions aligned to make the Arctic stratosphere especially cold (below -78°C), a key requirement for heavy ozone losses. In some parts of the polar stratosphere, temperatures plummeted to below -85°C. Researchers speculate that global warming, ironically, may be playing a role. When greenhouse gases trap heat near Earth's surface that energy does not rise to warm the stratosphere. Additional factors may act to keep that heat from rising, such as a paucity of winds and active atmospheric waves that could reach into the stratosphere and destabilize the polar vortex.
A key factor that causes ozone depletion to differ from one year to the next is temperature; this year, the polar vortex was very stable and its temperature especially frigid. When this happens, chlorine is converted from a benign form (known as "reservoir species") to a very reactive form ("radicals"). 2011 saw very high levels of radicals in the polar vortex, triggering lots of ozone depletion because when the vortex is cold and stable, polar stratospheric clouds of ice crystals can form. These cloud particles serve as the platform on which radicals instigate unusual reactions that break apart ozone. This year proved a good year for cloud formation. Unfortunately, even after the vortex breaks apart, it might take weeks for the radicals to dissipate, eventually shutting down ozone destruction.
Unfortunately, this Arctic ozone thinning is not without human impacts. Ozone-depleted Arctic air masses did not remain over the polar region alone; they recently drifted over southern Finland. Predictions were that the ozone-depleted stratospheric air masses might move over parts of Russia and perhaps extend to the Russian-Chinese border. Portions of Central Europe might also be affected, including regions as far south as the Mediterranean. Wherever these air masses moved, exposure on the ground to ultraviolet radiation increased with its attendant increase in skin cancer risk.
The science of ozone depletion has shown, once again, that it is not simple. The problem has unfortunately not been solved.
Further information can be found at http://europa.agu.org/?view=article&uri=/journals/gl/gl0404/2003GL018844/2003GL018844.xml&t=2004,rex, http://europa.agu.org/?view=article&uri=/journals/gl/gl0623/2006GL026731/2006GL026731.xml&t=2006,rex, http://books.google.com/books?id=52zXIwAUVa8C&pg=PA154&lpg=PA154&dq=ozone+depletion+arctic+cause+factors+weather&source=bl&ots=Tmfzbh9yDm&sig=BAukw-EWAXvJDJXj9PviHPKYuM4&hl=en&ei=SnqmTcL2LYuisAPDnoX5DA&sa=X&oi=book_result&ct=result&resnum=2&ved=0CB8Q6AEwAQ#v=onepage&q&f=false, http://www.sciencedaily.com/releases/2011/04/110405102202.htm, and http://cordis.europa.eu/fetch?CALLER=EN_NEWS&ACTION=D&RCN=33189.