Chemical reactions in the stratosphere involving chlorine and bromine from ozone depleting substances cause ozone in the southern polar region to be destroyed. This depleted region is known as the “ozone hole”. The stratospheric temperature and the amount of sunlight reaching the south polar region control the depth and size of the Antarctic ozone hole. This year, the stratosphere over Antarctica is warmer than the previous few years, so the ozone hole at present is smaller.
According to the Copernicus Atmosphere Monitoring Service (CAMS) the ozone hole has been particularly unusual as a sudden warming of the stratosphere disturbed the cold polar vortex that gives rise to the ozone hole. They expect that this year’s ozone hole will be one of the smallest holes since the mid-eighties.