Stretching 10.05 million square miles, the ninth largest ozone hole on record, the Antarctic ozone hole reached its annual peak on September 12, 2011. Its deepest point was recorded on October 9.
Annual monitoring of the South Pole ozone situation is achieved with the use of balloon-borne instruments, ground-based instruments and satellites by NASA and the National Oceanic and Atmospheric Administration (NOAA). The stratosphere is monitored for global levels of ozone as well as for levels of manmade chemicals that are contributing to the situation.
In a press release, the chief scientist for atmospheres at NASA's Goddard Space Flight Center in Greenbelt, MD., Paul Newman, said, "Even though it was relatively large, the area of this year's ozone hole was within the range we'd expect given the levels of manmade ozone-depleting chemicals that continue to persist in the atmosphere."
The most recent analysis, in the World Meteorological Organization and United Nations Environment Programme issued 2011 Quadrennial Ozone Assessment, shows that the hole over the Antarctic will probably persist one to two decades after the predicted recovery of the ozone in midcentury.