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Arctic ozone thins further

Thinning of the ozone layer over the Arctic this winter may lead to more ozone loss over Europe during spring, say scientists working on the Third European Stratospheric Experiment on ozone (THESEO 2000).

The team measured ozone losses of over 60% in the Arctic stratosphere, ...
Thinning of the ozone layer over the Arctic this winter may lead to more ozone loss over Europe during spring, say scientists working on the Third European Stratospheric Experiment on ozone (THESEO 2000).

The team measured ozone losses of over 60% in the Arctic stratosphere, 18km above the Earth's surface, during one of the coldest stratospheric winters on record. The data is now reinforcing the scientific community's concern that Arctic ozone levels may continue to decline despite international efforts to minimise stratospheric chlorine levels, following the Montreal Protocol.

THESEO 2000 is the largest ever field campaign to study ozone loss from the Arctic, bringing EU researchers together with experts form the United State's NASA-sponsored 'Solve' campaign, Canada, Japan and Russia. Using satellites, aircraft, balloons and ground-based instruments they have gathered data on the concentrations of ozone and other gases in the Arctic atmosphere.

Data collected mostly near Kiruna in Sweden reflected large ozone losses inside the Arctic stratospheric polar vortex during the 1999 to 2000 winter. The international research team used a number of techniques developed over the last decade to observe ozone levels in the lower stratosphere, including ground-based measurements and deployment of ozonesondes - lightweight ozone detectors designed to be flown on small weather balloons that gather data as the balloon rises. These instruments can often reach heights of 40 km without bursting, and have been used around the world to provide a long term time series of global data.

In March 2000, the World Meteorological Organisation Mapping Centre at the University of Thessaloniki reported that the mean column ozone amounts over Europe were 15% below the pre-1976 average.

THESEO satellite observations have now shown a clear ozone minimum over the polar region during February and March. In addition, their measurements showed the average polar column amount for ozone for the first two weeks of March was 16% lower than observed in the 1980s. The effect was, however, less dramatic above 20km altitude, according to the THESEO scientists.

Responding to the news, the European Commissioner for Research Mr Philippe Busquin said: 'European cooperation within an international team has made it possible to achieve these research results. They will provide the best possible scientific advice to the regulatory process concerning ozone depleting substances in the framework of the Montreal protocol and, equally important, to the citizens.'

The scientists remain concerned: Even as the stratospheric concentrations of chlorine and bromine decline, cold arctic winters and a more stable Arctic vortex may actually prolong depletion of ozone in the Arctic, they say.

Source: European Commission, Research Directorate-General.

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