Until working in Agroecology research (and learning a lot about the global Nitrogen-cycle) I thought we had solved the problem as well, simply by banning the use of CFCs.
We haven't.
The new problem for the antarctic ozone layer is nitrous oxide (N2O, laughing gas). N2O is released in large quantities from agricultural areas and adjacent water bodies, estuaries and coastal waters in a complex process that goes like this:
When you spread large amounts of nitrogen fertilizer onto fields you always have losses to ground and surface waters as the crops cannot take up all of the applied N (that is 'reactive' nitrogen in the form of different chemical compounds like ammonium, ammonia, nitrate, nitrite and others). The most important compound is nitrate (NO3-) and I'll focus on that. Leached nitrate is (together with organic carbon) eaten by denitrifying soil bacteria that turn it into denitrogen gas (N2) under aerated conditions. So far no problem. Nitrous oxide is released in addition to N2, when the oxygen in the soil solution is almost depleted as in all wet areas (streambanks, floodplains, deep lakes, estuaries, bottom layers of coastal waters). Laughing gas is no laughing matter:
In the stratosphere it has the same effect (albeit somewhat slower) as the CFCs we banned in the Montreal protocol... which is why the antarctic ozone layer will not heal anytime soon since we continue to increase the worldwide fertilizer application. Additionally, the CFCs are still up there - with an expected lifetime of about 50 years. We have some decades yet in which the original problem will persist... when they finally fade away, nitrous oxide should be available in the stratosphere in large enough quantities to continue the destruction.
This year we have a record ozone hole over the arctic as well. I'm sitting here in Denmark where there is a public advisory not to indulge in the first springtime warmth: the ozone concentration above northern Europe is approximately 30% lower than normal. The reason for this is somewhat different, namely extremely cold winter temperatures in the stratosphere above the arctic leading to the formation of stratospheric clouds that act as a catalyst for ozone destruction.
The icy stratosphere is likely a result of... global warming.
--> Greenhouse gases trap the heat in the troposphere (down here), thereby cooling the stratosphere.
Say hello to nitrous oxide once more, with its global warming potential 300 times higher than CO2.
So... hope I haven't bored you to death, but this is already horribly simplified (but essentially correct).
For in depth background:
The European Nitrogen Assessment ENA has just been finalized and here is the product of 5 years of research:
http://www.nine-esf.org/ENA-Book