The ozone hole is a seasonal phenomenon that starts to form during the Antarctic spring (August and September).
The September-October 2013 average size of the hole was 8.1 million square miles (21 million square kilometres). For comparison, the average size measured since the mid-1990s when the annual maximum size stopped growing is 8.7 million square miles (22.5 million square kilometres).
Paul Newman, an atmospheric scientist and ozone expert at NASAis Goddard Space Flight Center in Greenbelt, Md, said that there was a lot of Antarctic ozone depletion in 2013, but because of above average temperatures in the Antarctic lower stratosphere, the ozone hole was a bit below average compared to ozone holes observed since 1990.
The ozone hole forms when the sun begins rising again after several months of winter darkness. Polar-circling winds keep cold air trapped above the continent, and sunlight-sparked reactions involving ice clouds and chlorine from manmade chemicals begin eating away at the ozone.
Most years, the conditions for ozone depletion ease before early December when the seasonal hole closes.
--ANI (Posted on 26-10-2013)