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Measurements made by the agency's Envisat satellite found a peak loss in the ozone layer of 27.

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7 million tonnes, compared to 40 million tonnes last year, it says in a press release.

Ozone, a molecule of oxygen, forms a thin layer in the stratosphere, filtering out dangerous ultraviolet sunlight that damages vegetation and can cause skin cancer and cataracts.

Chemicals cause damage

The protective layer has been badly damaged by man-made chlorine-based chemicals.

The hole – in essence, a thinning of the layer – goes through a cycle each year as the chemical reaction that drives depletion peaks during the deep chill of the southern hemisphere winter, from late August to October.

In 2006, the ozone hole at its biggest measured 28 million square kilometres; in 2007, it was 24.7 million sq kms or roughly the size of North America.

Recovery not indicated

Ronald van der A, a senior project scientist at Royal Dutch Meteorological Institute (KNMI), says this year's improvement could not be seen as a confirmation that the ozone layer was in recovery.

"This year's ozone hole was less centred on the South Pole as in other years, which allowed it to mix with warmer air, reducing the growth of the hole, because ozone is depleted at temperatures less than -78 degrees celsius," he says.

Over the last decade, the ozone layer has thinned by about 0.3 per cent per year on a global scale.

Elimination deal

Last September 22, nearly 200 countries agreed to accelerate the elimination of hydrochlorofluorocarbons (HCFCs), a category of ozone-destroying chemicals.

Under the deal reached at a UN-sponsored conference in Montreal, developed countries will phase out the production of HCFCs by 2020 while developing states have until 2030 – 10 years earlier than previously promised.

The agreement changes the timetable that had been set in 1987 under the Montreal Protocol, which aims to eliminate the use of HCFCs and similar chemicals once commonly found in refrigerators, fire retardants and aerosol sprays.

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