New findings on the chemistry of chlorine radicals in the ozone hole

Researchers from Jülich and the Alfred-Wegener-Institute in Potsdam have now been able to clarify important details of atmospheric chemistry that are responsible for the decomposition of ozone in the lower stratosphere over Antarctica. The scientists showed by which chemical process the fraction of extremely reactive chlorine radicals in this layer of the atmosphere remains high. Increased chlorine radicals are the actual cause of ozone depletion. With these findings, the development of improved models for the future development of the ozone hole is possible. The well-known scientific journal Atmospheric Chemistry and Physics put the study on the list of "highlight articles".

In the Antarctic spring, the levels of chlorine radicals in the stratosphere remain consistently high. At the same time, however, large quantities of hydrogen chloride are also being built - a process in which chlorine radicals in principle would be decomposed. The researchers showed that there is a chemical zero cycle behind this: in this cycle chlorine radicals initially react to hydrogen chloride, which is then converted back into chlorine radicals.

The study contains important findings on the chemical cycle of chlorine radicals in the lower stratosphere and their importance for ozone depletion. They also show that other processes in the atmosphere, such as the increasing concentration of methane, are of minor importance.

Original publication:
Rolf Müller, Jens-Uwe Grooß, Abdul Mannan Zafar, Sabine Robrecht, and Ralph Lehmann: The maintenance of elevated active chlorine levels in the Antarctic lower stratosphere through HCl null cycles. Atmospheric Chemistry and Physics,18, 2985-2997, 2018;