Ozone hole splits in two, continues to shrink

5.45pm

WASHINGTON - This year's Antarctic ozone hole is the smallest one since 1988, but this has little to do with earthly activities and much to do with weird weather in the stratosphere, according to US government scientists.

The ozone hole has also split into two pieces, a new wrinkle on a phenomenon that scientists first observed in the 1970s, and have tracked as one measure of the impact of pollution.

The 2002 edition of the ozone hole covers about 16 million square kilometres, well below the 24 million square kilometres seen for the last six years at this time of year. Late September is generally the time scientists see the most ozone loss.

"This is smallest ozone hole since 1988, but that's still a lot of ozone loss," Paul Newman, an ozone researcher at NASA's Goddard Space Flight Center outside Washington, said yesterday.

The ozone layer shields Earth from the sun's harmful ultraviolet radiation, a cause of skin cancer in humans and potentially deadly to crops and animals. Without the ozone layer, there would be no life on this planet.

The small size of this year's ozone hole is caused by unexpectedly large weather patterns in the stratosphere, the layer of the atmosphere some 10 km to 48 km above Earth's surface where the ozone layer is found.

Normally, stratospheric weather in the extreme southern hemisphere is placid, allowing for a large ozone hole to open up, Newman said. This year, mammoth weather patterns pumped ozone into the south polar region and warmed it up.

"The warm air actually shuts down ozone loss," Newman said in a telephone interview.

The strange stratospheric weather also caused the ozone hole to divide into two lobes, instead of staying in one blob generally centred over Antarctica, he said.

The ozone hole is caused by the chemicals chlorine and bromine, which are contained in chloroflurocarbons and halons, human-made chemicals once used in hairspray, refrigerators and car air conditioners.

Chlorofluorocarbons and halons were banned in 1995 because of their destructive effect on the ozone layer, but they are so long-lasting that at this rate, the ozone hole will not disappear until 2050 or so, Newman said.

The coldest temperatures over the South Pole typically occur in August and September, when thin clouds form and chemical reactions help chlorine and bromine gases to rapidly destroy ozone. By early October, temperatures usually begin to warm, and after that the ozone layer starts to recover.

The National Aeronautics and Space Administration and the National Oceanic and Atmospheric Administration continuously observe Antarctic ozone with a combination of instruments, including balloons and satellites.

The ozone layer around the Arctic gets thin every year but is not considered to have a hole, Newman said.

- REUTERS

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