Storms Linked To Ozone Damage

Great plumes of water vapor injected into the stratosphere by powerful summer storms could be affecting atmospheric chemistry, triggering previously unrecognized damage to Earth’s protective ozone layer, scientists report (Science, DOI: 10.1126/science.1222978).

If such storms become more intense and frequent, as predicted by climate-change models, loss of stratospheric ozone would increase, exacerbating the already present dangers of exposure to UV radiation, conclude the paper’s authors, chemistry professor James G. Anderson and colleagues at Harvard University.

The researchers begin their chain of evidence with atmospheric data from a series of NASA aircraft missions over the U.S., taken during several summers over the past 10 years. The data show that convective storms frequently push large concentrations of water vapor into the stratosphere.

Extra humidity drastically alters the free-radical chemistry of bromine and chlorine, the primary destroyers of stratospheric ozone.

In particular, water vapor swells the liquid sulfate/water aerosols in the atmosphere that are the substrates of much stratospheric chemistry. The solubility of hydrochloric acid in the aerosols then increases. This condition makes it easier for chlorine to be transformed, through a chain of reactions involving chlorine nitrate, into the ozone-destroying, catalytically active free radical ClO∙. The researchers calculate that the extra humidity could result in ozone destruction rates two orders of magnitude greater than those in less humid conditions.

Paul O. Wennberg, a professor of atmospheric chemistry at Caltech, won’t speak directly to the coupling of climate change to ozone loss, but he says, “The tie between relative humidity and enhanced chlorine is secure.”

Ross J. Salawitch, a chemistry professor at the University of Maryland, agrees with the researchers’ observation that no aircraft missions currently study free radicals such as BrO∙ or ClO∙ in regions where storms have injected water over the U.S. Such measurements are needed to strengthen possible links between climate change and stratospheric ozone, he says.