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Ozone hole no bigger but more persistent

By CNN's Grant Holloway

WELLINGTON, New Zealand (CNN) -- The hole in the ozone layer above the Antarctic is no longer growing, but it may be staying around for longer.

New Zealand's National Institute of Water and Atmospheric Research (NIWA) told CNN Tuesday that this year's ozone hole was slightly smaller than last year's record, and was a more circular shape.

At 30 million square kilometers (12 million square miles) last year's Antarctic hole was the largest since records began in 1985.

The hole usually reaches its largest state around the end of September each year then gradually disappears. "When this year's hole was at its biggest extent it was a bit smaller than last year's," NIWA scientist Sylvia Nichol told CNN.

"At the moment the ozone hole is about the same size as last year's was at this time." Asia
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Because this year's hole was smaller, this suggests the hole may be staying around for slightly longer than in past years.

"Also this year's hole is a more circular hole; last year's was quite elliptical in shape," she said.

Ozone occurs in the stratosphere, between 10 and 30 kilometers above the earth's surface, forming a screen that absorbs ultra-violet radiation emitted by the sun.

However, since the late 1970s a hole in this screen has begun appearing early in the southern hemisphere's spring (September).

Ozone depletion is also happening over the Arctic region in the northern hemisphere, but to a lesser extent than in the south.

Radiation levels have increased up to 12 percent

The main cause of these holes has been the release into the atmosphere of chlorine, in the form of chloroflurocarbons, which reacts with and destroys ozone molecules.

More than half the ozone over the Antarctic can be destroyed each year in this way.

While the hole does not extend over populated areas of the southern hemisphere, the process of regenerating the hole depletes the ozone levels in countries such as Australia and New Zealand.

NIWA says that since 1980 ultra-violet radiation levels in New Zealand have increased by between 10 and 12 percent.

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