Increase in ozone destroying substances - but Montreal Protocol on track

Research from the University of Leeds and an international team of scientists has shown a recent increase in atmospheric hydrogen chloride (HCl), a substance linked to destruction of the ozone layer. It was anticipated that there would be a decline in HCl under the Montreal Protocol, the international treaty designed to protect the ozone layer by phasing out the production of ozone-depleting substances. Dr Emmanuel Mahieu from the University of Liège in Belgium, who led the research, explained: “It’s important to say that the Montreal Protocol is still on track, and that this is a transient reversal in the decline of HCl, which can be explained through a change in atmospheric circulation, rather than rogue emissions of ozone-depleting substances. The study explains that the unexpected increase is caused by a temporary but prolonged anomaly in atmospheric circulation, changing the balance between chlorofluorocarbons (CFCs) and their breakdown product HCl. Professor Martyn Chipperfield from the School of Earth and Environment at the University of Leeds, who led the modelling work for the study, said: “The expected deterioration of ozone-destroying chemicals in the atmosphere is certainly more complex than we had imagined. Rather than a steady decline, these findings have presented a rather more complicated picture. “Through comparison with detailed computer models, we have identified this decline as temporary due to changes in upper atmospheric wind patterns, so we remain optimistic that the ozone layer will recover during the second half of the century.