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Ozone loss reaches new recordPosted: 12 Oct 2006
The loss of ozone over Antarctica reached a new record in 2006, scientists with the European Space Agency (ESA) have announced.
The loss was caused by unusually low temperatures above Antarctica, the researchers said, and helped push the hole in the ozone layer to a near record size.
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| Ozone hole over Antarctica on 24 September 2006 when it reached its biggest ever size of 29 million km2. Photo credit: NASA |
"Such significant ozone loss requires very low temperatures in the stratosphere combined with sunlight," said ESA atmospheric engineer Claus Zehner. "This year's extreme loss of ozone can be explained by the temperatures above Antarctica reaching the lowest recorded in the area since 1979."
Measurements made by ESA's Envisat satellite revealed the ozone loss over Antarctica totaled 40 million metric tons, surpassing the record loss of 39 million tons recorded in 2000. The loss is calculated by measuring the area and the depth of the ozone hole.
NASA has reported that the size of this year's ozone hole reached a record 29 million square kilometres on 24 September.
Ozone is a protective layer about 15 miles above ground that shields the planet from harmful ultraviolet rays. It has been depleted primarily by human emissions of chlorofluorocarbons (CFCs,) once widely used as refrigerants, propellants and cleaning solvents.
CFCs themselves are inert, but ultraviolet radiation high in the atmosphere breaks them down into their constituent parts - such as chlorine - that can be highly reactive with ozone.
In the winter, the atmospheric mass above the Antarctic continent is typically cut off from exchanges with mid-latitude air by prevailing winds known as the polar vortex, leading to very low temperatures. In addition, during the cold and continuous darkness of this season, polar stratospheric clouds are formed that contain chlorine.
As the polar spring arrives, the combination of returning sunlight and the presence of polar stratospheric clouds leads to splitting of chlorine compounds into highly ozone-reactive radicals that break ozone down into individual oxygen molecules.
Ozone loss during this period is rapid - a single molecule of chlorine has the potential to break down thousands of molecules of ozone.
In November or early December, the winds surrounding the South Pole weaken, mixing ozone-poor and ozone-rich air, and reducing the hole.
Despite the findings that this year's loss reached a record, the longer-term outlook for the ozone hole is quite good. Scientists predict that full implementation of the 1987 Montreal Protocol, which bans CFCs and other ozone-depleting chemicals, should allow the ozone layer to recover by 2060.
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