Ask A Scientist Chemistry Archive

(Created prior to 1993)

Question: What is the mechanism by which CFC's (Chloral Fluoral Carbon) 
generated at or near sea level by "non-natural" sources effect high level 
ozone at or near the South Pole?   Most explanations about this issue do not 
fully explain how a dense, heavy molecule generated at moderate latitudes 
effect only ozone at high levels but not at sea level.  If CFC's are so 
unstable that they deteriorate, does not Pascal's law of fluid dynamics take 
over?  In that case should not levels of ozone be depleting evenly throughout 
our (almost) perfectly fluid atmosphere?
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This is a very detailed question, some references that may be 
able to help are:  "Chemistry of Atmospheres" by Richard P. Wayne (Clarendon 
Press, Oxford, 1991).  There is a whole chapter on ozone depletion and the 
"hole" over Antarctica.  First, it seems that there is some very unusual 
chemistry going on above the Antarctic!  The weather patterns there conspire 
to make this happen.  First, the low temperatures lead to the formation of 
polar stratospheric clouds, which are high-altitude.  The second is that as 
air cools and descends towards the poles in the winter, a vortex at the polar 
region is formed, with a westerly circulation at the South Pole.  This vortex 
has a very cold core, and anything that gets dumped into its interior, such as 
atmospheric chlorine radicals, (i.e., ClO) stays there for a long time.  This 
vortex comes and goes seasonally; it breaks down in November as the air gets 
warmer.  In other words, the vortex acts as a giant "reaction chamber" in 
which exotic reactions (which can only happen at low temperatures) have all 
the time in the world to happen.
Topper
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