DO COSMIC rays deplete the Earth鈥檚 protective ozone layer? The controversial theory that these high-energy particles drive the chemical reactions eating away at stratospheric ozone has just been given a boost.
Several years ago, a team led by of the University of Sherbrooke in Quebec, Canada, reported laboratory experiments suggesting that electrons liberated by cosmic-ray collisions could break down chlorofluorocarbon molecules, releasing chlorine atoms that tear ozone molecules apart. Chlorine production is usually thought to be triggered by UV light.
If Lu鈥檚 suggestion is correct, ozone levels should fall then rise every 11 years, in step with changes in cosmic-ray intensity driven by the 11-year solar cycle. Now Lu, who has moved to the University of Waterloo in Ontario, has found this correlation in NASA satellite data from 1980 to 2007 (). 鈥淭hey force one to conclude that the cosmic-ray mechanism plays the dominant role in causing the ozone hole,鈥� he says. Understanding the mechanism of ozone depletion should help scientists predict when ozone holes will grow or shrink, he adds.
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Atmospheric researcher Rolf M眉ller of the J眉lich Research Centre in Germany points out that the correlation in the satellite data might be spurious, though he concedes that cosmic rays might play a small role. 鈥淚t is worth investigating if the mechanisms identified in the laboratory carry over to the polar stratosphere,鈥� he says.