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Another cause of ozone depletion.

Last spring, scientists reported that atmospheric ozone, the airborne chemical that shields life on Earth from harmful solar radiation, had reached record low levels above much of the planet during 1992 and early 1993 (SN: 4/24/93, p.260).

Some scientists attribute this unexpected loss to droplets of volcanic sulfuric acid created by the eruption of Mt. Pinatubo in the Philippines in 1991. Adding to this debate, Ralf Toumi and his colleagues, all atmospheric chemists at the University of Cambridge in England, report in the Sept. 2 NATURE another possible mechanism to explain ozone depletion. Chlorine nitrate, a natural atmospheric compound, accounts for a greater proportion of ozone depletion than previously recognized, they maintain.

"Chlorine nitrate is an active agent in ozone depletion, which has not been realized before," Toumi says. Chlorine nitrate forms over the polar regions during winter, then drifts toward the equator, where according to Toumi it destroys ozone slowly over a wide area. "This cycle is slower than the other polar ozone depletion cycles, but its potential influence is far ranging," Tuomi says. Chlorine nitrate could have a great effect in Earth's warmer latitudes, he says, accounting "for a sizable portion of the ozone depletion that has so far not been explained."

Toumi believes current climate-change models should add the chlorine nitrate cycle to assess the compound's long-range impact. Since measured ozone depletion "has been far outstripping the models," he says, "the challenge has been to explain the changes at lower latitudes. This mechanism should account for some --though certainly not all -- of the unexplained ozone changes."
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Title Annotation:chlorine nitrate forming naturally in polar regions during winter
Author:Lipkin, Richard
Publication:Science News
Article Type:Brief Article
Date:Sep 11, 1993
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