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Lower levels of atmospheric cleanser.

Hydroxyl radicals (OH) play the role of atmospheric janitor: They react with scores of gases, removing both pollution and natural compounds from the air. They reduce the levels of certain greenhouse gases and also some ozone-harming chemicals. But new research indicates that scientists have overestimated global levels of OH.

Atmospheric concentrations of OH change so rapidly that chemists cannot assess its levels by measuring the compound itself. Instead, they calculate its concentrations by gauging levels of methyl chloroform, a pollutant that reacts with OH. The less methyl chloroform, the higher the OH level.

This approach is based on the assumption that the OH reaction is the only one removing methyl chloroform from the atmosphere. However, measurements made in the tropical Pacific now show that reactions in the ocean also reduce atmospheric methyl chloroform, reports James H. Butler of the National Oceanic and Atmospheric Administration in Boulder, Colo. The new findings reveal that global OH levels range 5 to 10 percent lower than once thought - an indication the atmosphere cannot itself of key pollutants as quickly as experts had believed. The revision will affect current efforts to replace ozone-destroying chlorofluorocarbons with less destructive industrial chemicals. If the substitutes survive longer in the atmosphere than previously assumed, they will harm the ozone layer more than scientists had estimated, Butler warns.
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Title Annotation:hydroxyl radicals
Publication:Science News
Date:Aug 10, 1991
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