Some time ago a post appear asking about the amount of ozone destroyed by
a single Cl atom. I don't recall seeing a reply, but I just picked up a
book that explains the entire process very well.
Earth Under Seige, by Richard P. Turco, Oxford Univ. Press, 1997
For those of you interested in these kinds of problems I recommend the book
highly. Very thorough and with much more complete explainations than are
given in more popular publications.
The quickndirty answer to the ozone question is that Cl acts as a catalyst
so in principle a single Cl can destroy an unlimited amount of ozone.
However, there is some hydrogen up there with the ozone and hence a chance that
a CL will find an H instead of ozone and make HCl. Then there is a chance
that the HCl will wander back to the troposphere and get washed out by rain.
On the average it takes 100 yrs to wash out a Cl, so in the meantime they
can mess up a lot of ozone. Another interesting item is that on the average
all the ozone is destroyed and regenerated every hour! Thus, even a small
shift in the rate of creation or destruction can add up in a hurry.