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Ozone-Depleting Chemical on the Rise

The amount of hydrogen chloride in the stratosphere – an atmospheric layer at an altitude of 15–45 km – has been increasing over the Northern Hemisphere since 2007, according to a report in Nature.

Co-author Prof David Griffith of The University of Wollongong’s Centre for Atmospheric Chemistry said the increase in hydrogen chloride, which leads directly to ozone depletion by releasing chlorine in the stratosphere, is a result of a temporary but prolonged anomaly in atmospheric circulation.

The findings are based on measurements by a network of ground-based remote sensing stations at a number of locations around the world. An analysis of these measurements, combined with satellite observations and model simulations, revealed that although chlorine concentrations in the Northern Hemisphere are on the rise, those in the Southern Hemisphere are continuing to decrease, as expected from measures agreed to under the Montreal Protocol.

The Montreal Protocol is an international treaty that banned the production of major ozone-depleting substances worldwide. The large ozone loss over Antarctica was the key observation that stimulated its drafting and signing in 1987.

Griffith said the research dismisses the possibility that rogue emissions of ozone-depleting substances are at play. “The study confirms that the Montreal Protocol remains a success and that the ozone layer is likely to fully recover during the second half of this century,” he said.

“However, our results show that atmospheric variability and perhaps climate change can significantly modify the path towards full recovery. It will be a bumpy ride rather than a smooth evolution.”