Researchers question cause of ozone hole


Researchers question cause of ozone hole

Saturday, 28 July 2007


Some British researchers are questioning the extent to which man-made
chemicals are mainly responsible for the "ozone hole" that forms over
Antarctica each winter and exposes New Zealanders to cancer-causing
radiation as it breaks up each summer.

Chemists from the University of Leeds, the University of East Anglia
and the British Antarctic Survey reported finding high concentrations
of natural ozone-depleting chemicals: halogens such as bromine and
iodine oxides.

"The springtime peak of iodine oxide - 20 parts per trillion - is the
highest concentration recorded anywhere in the atmosphere," said an
abstract of their study, published in the journal Science on Thursday.

Scientists have repeatedly said that the ozone depletion is driven by
chemicals such as chlorofluorocarbons (CFCs) produced by humans
breaking down the ozone layer.

Last year, the UN Environment Programme Ozone Secretariat said in 2006
the depletion of the ozone over Antarctica ` "cannot be explained by
natural cycles but is caused by the impact of synthetic chemicals in
the stratosphere."

This was why CFCs were banned under the Montreal Protocol in 1987, but
it is expected to take another 50 years to return the ozone layer to
pre-1980 levels over New Zealand.

Now the British research has shown that large quantities of ozone-
depleting bromine came from sea salt and iodine oxide from "almost
certainly bright orange algae that coat the underside of the sea ice
around the continent" .

These halogens deplete the ozone above the ice surface, which reduce
the capacity of the atmosphere to remove certain chemical compounds.

"We still have to work out what the ramifications of this discovery
are," said John Plane, professor of atmospheric chemistry at the
University of Leeds.

The chemists did an 18-month study of the lowest part of the
atmosphere on the Brunt Ice Shelf, about 20km from the Weddell Sea.

The scientists projected a beam of light across the shelf, and
analysed the levels of chemicals in the reflected light. They said
satellite observations by team member Alfonso Saiz-Lopez "have
confirmed that iodine oxides are widespread throughout coastal
Antarctica."

New Zealand scientists track the Antarctic ozone `hole' each winter
using satellite data and ground-based measurements from their
instruments at the Antarctica NZ site at Arrival Heights, in
Antarctica. When the `hole' in 24km above the Earth in the
stratosphere breaks up in early summer, ozone-depleted air thins out
the ozone at mid-latitudes - above New Zealand - over the summer.

New Zealanders are exposed to UV intensities in summer about 50
percent greater than in comparable latitudes in Europe, and 40 percent
greater than in comparable locations in North America.


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© Fairfax New Zealand Limited 2007

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