[Looking for Diogenes]

The graph [above] shows the measured total ozone above the Halley Bay station in Antarctica. Each point represents the average total ozone for the month of October. Note the sudden change in the curve after about 1975. By 1994, the total ozone in October was less than half its value during the 1970s, 20 years previous. This dramatic fall in ozone was caused by the use of man-made chemicals known as 'halogens' which include the well-known CFCs commonly used in fridges and so on. These CFCs had made their way into the upper atmosphere where the much stronger UV radiation from the Sun had broken them down into their component molecules, releasing the potentially damaging chlorine (and bromine) atoms, which, given the right conditions, could destroy ozone.
Cambridge University, Centre for Atmospheric Science

[Kermit]

I've never bought the Ozone Hole anyway. The sun makes ozone in a chemical reaction with the Earth's atmosphere. During the Antartic winter, there is very little sunlight, which causes a reduction in the amount of ozone.

Second, I may be wrong, but I thought CFC's were heavier than air and were overwhelmingly used in the northern hemisphere. How did the CFC's get to the southern hemisphere and up to high altitudes is sufficient quantities to affect the amount of ozone?

Why would that '75 law have an immediate effect? How much CFC's were still on the market, as the supply was used up? How long would it take for a CFC used by a consumer in Canada at ground level take to get to the southern hemisphere and up to the high altitude needed to have an effect?