Cosmic rays are eating away at the Earth?s protective ozone layer, according to Canadian radiation scientists Qing-Bin Lu and Leon Sanche of the University of Sherbrooke. They claim to have discovered an important process underlying the growing ozone hole over the southern hemisphere. But atmospheric scientists are not so sure.

Lu and Sanche analyzed ozone and cosmic ray data taken from ground stations, weather balloons and satellites. In a paper in Physical Review Letters, they report a strong correlation between cosmic ray intensity and ozone depletion across different levels of the atmosphere and different latitudes. They also found that changes in ozone concentration matched fluctuating cosmic ray intensity between 1979 to 1992.

They propose that cosmic rays contribute to ozone depletion through their interactions with human-made chlorofluorocarbons (CFCs) in the atmosphere. Electrons created by cosmic rays break down CFC molecules, leading to the production of chorine atoms, which in turn break down ozone. Ultraviolet radiation from sunlight destroys ozone in a similar way.

Lu and Sanche found evidence for their model in a laboratory simulation of the conditions found in Antarctic clouds. They cooled a metal bar to -170

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