Ozone is a protective atmospheric layer found in about 25 kilometers altitude that acts as a sunlight filter shielding life on Earth from harmful ultraviolet rays, which can increase the risk of skin cancer and cataracts and harm marine life.
The depletion of ozone is caused by extreme cold temperatures at high altitude and the presence of ozone-destructing gases in the atmosphere such as chlorine and bromine, originating from man-made products like chlorofluorocarbons (CFCs), which were phased out under the 1987 Montreal Protocol but continue to linger in the atmosphere.
This year, the area of the thinned ozone layer over the South Pole reached about 27 million square kilometers, compared to 25 million square kilometers in 2007 and a record ozone hole extension of 29 million square kilometers in 2006, which is about the size of the North American continent.
Depending on the weather conditions, the size the Antarctic ozone hole varies every year.
During the southern hemisphere winter, the atmosphere above the Antarctic continent is kept cut off from exchanges with mid-latitude air by prevailing winds known as the polar vortex - the area in which the main chemical ozone destruction occurs.
The polar vortex is characterized by very low temperatures leading to the presence of so-called stratospheric clouds (PSCs).
Julian Meyer-Arnek of the German Aerospace Centre (DLR), which monitors the hole annually, explained the impact of regional meteorological conditions on the time and range of the ozone hole by comparing 2007 with 2008.
"In 2007, a weaker meridional heat transport was responsible for colder temperatures in the stratosphere over the Antarctic, leading to an intensified formation of PSCs in the stratosphere," Meyer-Arnek said.
"Therefore, we saw a fast ozone hole formation in the beginning of September 2007," he added.
"In 2008, a stronger-than-usual meridional heat transport caused warmer temperatures in the Antarctic stratosphere than usual, reducing the formation of PSCs. Consequently, the conversion of chemically inactive halogens into ozone-destroying substances was reduced. As a result, in the beginning of September 2008, the ozone hole area was slightly smaller than average," he explained.
"Since the polar vortex remained undisturbed for a long period, the 2008 ozone hole became one of the largest ever observed," said Meyer-Arnek.