Cosmic rays linked to ozone hole

2019-03-06 06:09:21

By Greg Miller Cosmic rays are eating away at the Earth’s protective ozone layer, say 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 analysed ozone and cosmic ray data taken from ground stations, weather balloons and satellites. In a forthcoming 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 manner. 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 below -170 °C and condensed water vapour and CFCs onto its surface. When they then bombarded this “cloud” with low-energy electrons like those produced by cosmic rays, chlorine was produced. “We believe this could be the major mechanism for the creation of the polar ozone hole,” Lu says. For example, he says, the cosmic ray effect could explain why CFC and ozone levels decline during the Antarctic winter, when ultraviolet radiation is scarce. However, atmospheric scientists are far from convinced. Neil Harris of the European Ozone Research Coordinating Unit in Cambridge, England says: “It is hard to see how this mechanism would have a significant atmospheric effect.” Harris says many lines of evidence indicate that the reduction of CFCs in the upper atmosphere during the winter months is due to downward air currents, not chemical processes. In addition, he says, since CFCs are not particularly soluble in water, they would not be present in cloud-born ice particles in very high concentrations,