Paris: An ozone hole five times the size of California opened over the Arctic this spring, matching ozone loss over Antarctica for the first time on record, scientists said.

Formed by a deep chill over the North Pole, the unprecedented hole at one point shifted over eastern Europe, Russia and Mongolia, exposing populations to higher, but unsustained, levels of ultra-violet light.

Ozone, a molecule of oxygen, forms in the stratosphere, filtering out ultraviolet rays that damage vegetation and can cause skin cancer and cataracts.

The shield comes under seasonal attack in both polar regions in the local winter-spring.

Part of the source comes from man-made chlorine-based compounds, once widely used in refrigerants and consumer aerosols that are being phased out under the UN's Montreal Protocol.

But the loss itself is driven by deep cold, which causes water vapour and molecules of nitric acid to condense into clouds in the lower stratosphere.

These clouds in turn become a "bed" where atmospheric chlorine molecules convert into reactive compounds that gobble up ozone.

Ozone loss over the Antarctic is traditionally much bigger than over the Arctic because of the far colder temperatures there.
In the Arctic, records have -- until now – suggested that the loss, while variable, is far more limited.

(Agencies)