<P> 1, 1, 1 - Trichloro - 2, 2, 2 - trifluoroethane, also known as CFC - 113a, is one of four man - made chemicals newly discovered in the atmosphere by a team at the University of East Anglia . CFC - 113a is the only known CFC whose abundance in the atmosphere is still growing . Its source remains a mystery, but illegal manufacturing is suspected by some . CFC - 113a seems to have been accumulating unabated since 1960 . Between 2010 and 2012, emissions of the gas jumped by 45 percent . </P> <P> Scientists have attributed ozone depletion to the increase of man - made (anthropogenic) halogen compounds from CFCs by combining observational data with computer models . These complex chemistry transport models (e.g. SLIMCAT, CLaMS--Chemical Lagrangian Model of the Stratosphere) work by combining measurements of chemicals and meteorological fields with chemical reaction rate constants . They identify key chemical reactions and transport processes that bring CFC photolysis products into contact with ozone . </P> <P> The Antarctic ozone hole is an area of the Antarctic stratosphere in which the recent ozone levels have dropped to as low as 33 percent 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 polar vortex, over 50 percent of the lower stratospheric ozone is destroyed during the Antarctic spring . </P> <P> 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 polar stratospheric clouds (PSCs). </P>

Where is the ozone layer depleted the most
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