MadSci Network: Earth Sciences
Query:

Re: Why is the ozone hole formed above Antarctica?

Date: Mon Feb 16 14:27:02 2009
Posted By: Edward Hyer, Post-doc/Fellow, Aerosol Group, Marine Meteorology Division, Naval Research Lab
Area of science: Earth Sciences
ID: 1232876099.Es
Message:

Daphne,

Basically, the conditions above the South Pole are unique in how they
permit dramatic ozone depletion. During the polar winter, when sunlight is
absent, the air over the pole gets cold enough that chemicals that could
remove chlorine freeze and form clouds. This is "de-nitrification" and it
has two consequences: first, the clouds formed by the freezing chemicals
speed up the reactions that turn chemically inert CFCs into reactive free
chlorine. Second, the clouds of frozen chemicals become heavy and sink,
leaving the chlorine. Once the sunlight returns, the built-up chlorine
begins reacting very quickly to destroy ozone, and this is why there is an
"ozone hole" over Antarctica from August (the end of Antarctic winter)
until November.

You can find a more complete description of this process here (it's pretty
complicated): http://www.atm.ch.cam.ac.uk/tour/part3.html




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