February 28, 2007
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FROM VOLUME 5, NUMBER 6, JUNE 1992
NORTHERN HEMISPHERE OZONE
Major results are in from the U.S. and
European studies on stratospheric ozone conducted over the past winter using
aircraft, satellite, ground-based and balloon measurements.
Researchers from the U.S. National Aeronautics and Space Administration
reported in late April that Arctic ozone loss reached about 10 percent this
winter. In February 1992, they had warned that the presence of cold temperatures
in the weeks ahead, together with increasing levels of sunlight, could lead to
even more serious depletion. This conclusion was based on the discovery over the
Arctic of unexpectedly high levels of chlorine monoxide (ClO), resulting from
anthropogenic emissions. (See GLOBAL CLIMATE CHANGE DIGEST News, Mar.
1992.) In the presence of sunlight and particles that form at low temperatures,
ClO is considered a key ingredient in ozone destruction. Because of an early
warming in the Arctic stratosphere this winter, temperatures cold enough for
ozone destruction were present only about half as long (39 days) as usual.
However, the potential for more serious losses in future years still exists, as
For the Northern Hemisphere, satellite measurements of the total amount of
ozone hit a record low in January and February, and were 10-15 percent below
normal in February. Particles from the eruption of Mount Pinatubo are thought to
have had a measurable but not major effect on ozone loss. Results of the U.S.
study are discussed in Sci. News, p. 308, May 9, 1992; Science,
p. 734, May 8; Eos, p. 210, May 12; Intl. Environ. Rptr., p.
245, May 6.
Results of the European Arctic Stratospheric Experiment, involving
scientists from 17 countries, show that ozone over much of Europe (including
some cities) thinned by a record 10-20 percent last winter. Contributing to the
loss was the presence of an extremely large high-pressure system over Europe and
the North Atlantic during December and January, but anthropogenic chemicals are
considered a major ingredient as well. Researchers expect to untangle these
factors and the influence of Mount Pinatubo particles over the next few months.
(See Nature, p. 552, Apr. 16, 1992; New Scientist, p. 5, Apr.
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