ozone depletion

[helghast]

why is the ozone hole over antarctica and not over other places?

[pedant]

Ozone depletion is not restricted to Antarctica. A hole has also been detected above the Artic ice cap and ozone depletion has been measured in the Northern Hemisphere. However the nature of Antarctica ensures that Ozone depletion is more pronounced and that the 'hole' that develops is sustained over a longer period.

During the Antarctic winter the air masses over the continent form what is called the polar vortex. This, as the name implies, is a rotating mass of air over the continent, and serves to isolate the air, and hence ozone, within it.

Without sunlight during the winter the temperatures can obviously fall to extremely low levels within the vortex. These low temperatures are required for the formation of polar stratospheric clouds (PSC). There is no clear scientific consensus as to exact composition of these clouds but it is generally agreed that the nitric acid and nitric acid trihydrides in the PSCs enable chlorine (from CFCs etc) and to a lesser extent bromine to form much more active compounds than they otherwise would have. This results in a much greater depletion of ozone.

As already mentioned the ozone within the area covered by the polar vortex cannot be replaced by diffusion from the ozone outside the polar vortex because of its isolating effect. Thus the ozone within the area covered by the polar vortex can only be replaced by the reappearance of the sun which forms ozone and the disappearance of the polar vortex during the summer months resulting in ozone diffuses in from areas of higher concentrations.

If you want further details have a look at this site http://www.atm.ch.cam.ac.uk/

[Canas]

i don't know

[Peter Pedant]

Pedant is different to peter pedant, and reading his answer, he seems to be brighter as well!

[JohnPPotts]

The centrifugal force of the Earth will tend to make the atmosphere thinner at the poles (in the same way that the Earth itself is thicker around the equator), so as the ozone layer depletes it will tend to be thinnest over the poles.