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Global Climate Change Digest

A Guide to Information on Greenhouse Gases and Ozone Depletion
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Item #d92mar94

At a February 3, 1992, press conference, NASA scientists presented results from this winter's Airborne Arctic Stratospheric Expedition and from NASA's Upper Atmosphere Research Satellite, launched last September. They concluded that an ozone hole is likely to form over populated regions of the Northern Hemisphere sometime within the next decade. Chlorine monoxide (ClO), the substance most effective in ozone destruction, was found over northern New England and Canada at levels higher than ever observed, even in the Ant-arctic ozone hole. Similarly high levels persisted over northern Europe for a period in January. Such high levels of ClO, which were found in the Arctic stratospheric vortex, can lead to ozone destruction of 1 to 2 percent per day, but only in the presence of sunlight. The formation of an Arctic ozone hole depends on persistence of the vortex into March, which would permit sunlight to act on the high levels of ClO it contains. Scientists feel it is only a matter of time before this happens.

There were other surprises. Two different chemical reactions known to inhibit the destructive action of ClO were found to be less effective than expected, and thin sheets of air high in ClO were observed as far south as the latitude of Cuba.

The high levels of ClO are thought to be partly a result of the recent abundance of stratospheric aerosol particles, which provide surfaces for reactions that generate ClO and which are in unusually good supply following the June eruption of Mount Pinatubo. (See Prof. Pubs./Mt. Pinatubo ERuption, this GLOBAL CLIMATE CHANGE DIGEST issue--Mar. 1992.) Levels of ClO are likely to keep rising through the next decade, regardless of any modifications that might be made to the Montreal Protocol.

See Science, pp. 797-798, Feb. 14, 1992; Sci. News, p. 84, Feb. 8; Intl. Environ. Rptr., pp. 59-60, Feb. 12; Global Environ. Change Rep., pp. 1-3, Feb. 14.

An interim report issued in early February from the European Arctic Stratospheric Experiment stated that ozone amounts are lower than expected based on measurements in previous years, and could drop to record low levels later in the winter. (New Scientist, p. 16, Feb. 8.)

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