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Perhaps this should be a chemistry question, but it seems to have physics attributes. There's a perennial ozone "hole" around the south pole created by destruction from Cl based chemicals like CFCs. Given that most CFC emissions originated in the northern hemisphere, why isn't there a significantly similar effect around the north pole?

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And what is evidence, that that hole is not older? –  Georg Apr 25 '11 at 15:06
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The relationship between ozone depletion and CFC emissions is and has long been established science. –  Colin K Apr 25 '11 at 15:45
    
There's a ozone hole in the Arctic as well. They aren't constant, though, but oscillate with the time of the year. –  Lagerbaer Apr 25 '11 at 15:49
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@Colin K is correct. In fact I remember the days when the CFCs ban went into effect. It was sometime in the early 90s if memory serves ... as it does, the Montreal protocol banning CFCs was signed in 1987. Thanks to the ban much of the population living near and below the polar regions was saved from a disastrous epidemic of skin cancer. As for how do we know why it is not older? Because [we looked](en.wikipedia.org/wiki/…. –  user346 Apr 25 '11 at 16:00

3 Answers 3

up vote 7 down vote accepted

From the Wikipedia article:(My emphasis)

Some people thought that the ozone hole should be above the sources of CFCs. However, CFCs are well mixed globally in the troposphere and the stratosphere. The reason for occurrence of the ozone hole above Antarctica is not because there are more CFCs concentrated but because the low temperatures help form polar stratospheric clouds.[82] In fact, there are findings of significant and localized "ozone holes" above other parts of the earth.[83]

The chemical processes are complicated and involve UV-dissociation of the CFCs to release chlorine which then destroys the ozone. However:

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).

The first quote states that the conditions over the Antarctic are more favorable for the chemical process of ozone depletion to occur.

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I think processes on the ice particles of the PSCs are impicated. It is mainly a springtime phenomena, as the UV hits the still cold upper atmosphere. Differences in circulation make the Antarctic more susceptable than the Arctic, however the last couple of years have been favorable for norther hemisphere ozone holes. –  Omega Centauri Apr 25 '11 at 15:59
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As I said, the processes are complicated. The Wikipedia article is well-referenced and explains it in sufficient detail, with the main emphasis on the role of the PSCs. –  Lagerbaer Apr 25 '11 at 16:00
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Lagerbaer: Thank you for the interesting site. I didn't know the arctic ozone depletion was so variable. –  Michael Luciuk Apr 25 '11 at 16:18
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Unnecessarily argumentative side comments removed. –  dmckee Apr 26 '11 at 21:19

Sometimes the world of physics is influenced by the 'real politik' and I bold read in the same WP-Ozone link:

A critical DuPont manufacturing patent for Freon was set to expire in 1979 ... The United States banned the use of CFCs in aerosol cans in 1978...
Dr. Mostafa Tolba, former head of the UN Environment Programme, who was quoted in the 30 June 1990 edition of The New Scientist, '...the chemical industry supported the Montreal Protocol in 1987 because it set up a worldwide schedule for phasing out CFCs, which [were] no longer protected by patents. This provided companies with an equal opportunity to market new, more profitable compounds.'"

Simply put: without regulation = small business due to the low manufacturing price; with regulation = new protected compounds and big business, as usual;

The subject was born, grew up in a short time and bore fruits (a regulation and a Nobel). It is now almost dead and buried.
Now back to physics speculation:
I wonder: Would have been ruled out other possible explanations for the phenomenon? For example: variation of the Earth magnetic axis, some characteristic of the solar cycle, cosmic rays, a mix of causes, etc...
As protons and electrons are differently attracted to North and South magnetic Poles a distinct pattern could arise and explain your question in a different way.

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this is because the gases that are heavier than air, sink to the bottom of the globe thanks to the centrifugal effect of the earths rotation.

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-1 for nonsense. –  Georg May 2 '11 at 12:42

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