Study: Atmosphere losing ability to clean itself

By Richard Stenger
CNN

(CNN) -- A compound that naturally rids the air of pollutants has become increasingly scarce in the global atmosphere in the past decade, according to a new scientific report.

The beneficial cleanser destroys many artificial contaminants in the air such as carbon monoxide, sulfur dioxide and nitrogen dioxide. It also eats up many gases involved in ozone depletion and the greenhouse effect.

Levels of the chemical -- the hydroxyl radical known as OH, the dominant oxidizing compound in the lower atmosphere -- dropped considerably more in the Northern Hemisphere than the southern one, the researchers said.

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"The overall negative acceleration in the global OH trend is dominated by changes in the Northern Hemisphere and suggests an anthropogenic cause for major OH variations," the scientists wrote in the May 4 edition of the journal Science.

The amount of OH in the less developed south was on average between 14 and 35 percent higher than the north, concluded the scientists, led by Ron Prinn of the Massachusetts Institute of Technology.

Global OH levels fell about 10 to 24 percent between 1979 and 2000, the international team determined.

Evidence that humans contributed

While the north-south disparity suggests that human activities contributed to the decline of the natural air cleanser, other findings left the scientists puzzled.

Global OH likely rose between 1979 and 1989 before beginning a dramatic and puzzling drop over the next 11 years to the lowest levels since measurements began in 1978.

"These variations imply important and unexpected gaps in current understanding of the capability of the atmosphere to cleanse itself," the authors said.

"This has important implications for the mitigation of air pollution of climate change."

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Massachusetts Institute of Technology

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