Chink in the armour

Recent measurements show that protective ozone levels in the atmosphere touched a record low early this year

Published: Friday 31 March 1995

PROVISIONAL data gathered from over 95 Earth-based stations of the World Meteorological Organisation (WMO) reveal record low ozone levels during most of January and the first half of February over Siberia and western Europe.

Ozone deficiencies during the second half of January, says Rumen Bojkov, special advisor to the WMO secretary-general, fell 35 per cent below normal over Siberia, while ozone levels over Europe were 20 per cent lower than normal. Over North America, ozone levels were 5-10 per cent lower than usual; but at times the ozone values fell by as much as 20 per cent.

Previous studies have shown that winter-spring ozone values in the northern middle and polar latitudes could be as much as 6-8 per cent below long-term averages. "However, now we have observed a 20 to 35 per cent deficiency, which could be attributed to chemical ozone destruction", says Bojkov.

"With the availability of chlorine oxide -- a byproduct of humanmade chlorofluorocarbons (CFCs) -- transported from the Arctic to Europe and Siberia, chemical ozone destruction is quite possible. The extremely low ozone values in the northern mid-latitudes this winter are in part aggravated by the hampering of the transport of ozone-rich air from the equatorial stratosphere," says Bojkov.

Although most countries have agreed under the Montreal Protocol to phase out by this year-end ozone destructive chemicals such as CFCs, chlorine concentrations in the higher atmosphere will continue to rise to peak values by the turn of this century. "During the next 10 years, the worst of ozone destruction is expected to occur especially during periods with very low temperatures in the higher atmosphere," says Bojkov.

Despite extremely low ozone values, scientists at the WMO feel that there is no need for special measures against a possible increase in ultraviolet radiation, because the sun is relatively low in this region and the sky is frequently overcast.

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