The ozone layer has very important function for all life on our planet by protecting the Earth's surface from harmful ultraviolet radiation. The levels of ozone-depleting chemicals have been shrinking since the 1987 Montreal protocol but there is still a significant ozone hole over Antarctica.
The scientists have measured that this year's Antarctic ozone hole reached its annual peak on September 12, by covering 10.05 million square miles, the ninth largest on record. This year's lowest ozone level readings were recorded on October 9 and were 102 Dobson units.
The levels of ozone-depleting chemicals have been steadily declining in the last two decades but many of these chemicals have very long lifespan, and can remain in atmosphere for decades.
Many scientists across the globe believe that ozone layer has already started its recovery. In fact according to the current atmospheric models by the World Meteorological Organization it is expected that stratospheric ozone could recover by the middle of this century. However, the ozone hole above Antarctica could still persist two decades beyond that and should completely disappear somewhere around 2070.
The ozone layer recovery trend isn't expected to go smoothly because of natural cycles in temperatures and several other factors that affect depletion of the ozone.
The scientists have observed ozone depletion phenomena for more than 30 years and the most expressed decrease in ozone has been in the lower stratosphere. The chemicals mostly responsible for ozone depletion are chlorofluorocarbons.
The ozone hole occurs during the Antarctic spring, from August/September to early December, as strong circumpolar winds start to circulate around the continent and create an atmospheric container. Most years, the conditions for ozone depletion ease by early December, and the seasonal ozone hole closes.
The measurements tracking ozone depletion are made from the ground, in the atmosphere itself and by satellite. NASA, for instance, measures ozone levels in the stratosphere with the help of Ozone Monitoring Instrument (OMI) aboard the Aura satellite.