The phenomenon was worst between 1998 and 2006 and ozone levels in the hole area seem to be gradually recovering.
The hole forms and expands over the Antarctic during the Southern Hemisphere spring between August and September.
The depletion of the ozone layer became a cause of international concern because it is needed to shield life on Earth from potentially harmful ultraviolet radiation that can cause skin cancer and damage plants.
The Montreal Protocol of in 1987 aimed to protect the ozone layer by reducing production of substances responsible for depleting it, such as chlorine and bromine, found in chlorofluorocarbons and halons.