The main culprit in the destruction of the ozone layer is chlorofluorocarbons, otherwise known as CFCs.  CFCs are especially dangerous, because they are such stable molecules.  They stay in the atmosphere for a long time. . .decades to even centuries.

When CFCs are exposed to ultraviolet radiation, they release highly reactive chlorine atoms.  These chlorine atoms enter into a repeating cycle of reaction with ozone.  After reacting with ozone, they re-emerge unchanged, producing oxygen as a result of the reaction.

The region over Antarctica is especially vulnerable to ozone depletion, due to the exceptionally cold temperatures (-85 to -90 degrees C)  Because of these low temperatures, the stratospheric temperatures are low enough to create ice crystals at high altitudes.  Given the presence of the ice crystals, ozone and chlorine containing molecules are trapped in the crystals.  When springtime comes, and the temperatures drop, the ozone and the chlorine molecules are in close proximity, allowing them to react with each other in greater quantities.  This is why there is a significant ozone hole over the southern pole of the earth.

These are scientists making calculated observations about the status of the ozone layer over Antarctica.