I'm never looking for a fight, but I suggest reading the Web site that I offered in my reply. A general decrease in ozone concentration has been observed everywhere in the stratosphere, on the order of 5%, but polar conditions are such that ozone concentration is dramatically reduced in September-October of each year. The reactions with chlorine that is derived from CFCs have been studied, tested, and verified.
Now there is a very strong correlation between volvanic avtivity and ozone thinning in the respective hemisphere, particularly if the valvanoes in question are very active and generate a lot of chlorine. Measurable ozone thinning in the north did occurr, for example, after the very large Mt Pinatubo eruption. It just happens that the most active volcanoe in the world is Mt Erabus in, you guessed it, Antarctica. It's been more or less continuously erupting for decades.
Erebus has a lava lake, which is why it has been continuously erupting. Erebus emissions are low-level and never reach the stratosphere, and the form of chlorine is HCl, which is volatile and doesn't persist in the atmosphere. Pinatubo's violent eruption did inject a large amount of SO2 into the stratosphere, which had an effect on the ozone concentration for about 3 years after the eruption.
A general decrease in ozone concentration has been observed everywhere in the stratosphere, on the order of 5%, but polar conditions are such that ozone concentration is dramatically reduced in September-October of each year.
Without having looked, does this site explain why this reduction occurs in the South Pole (not near CFC sources)rather than the North (where there are lot's of them)?