Sensitivity of Arctic ozone loss to stratospheric H 2 O

Likely causes of a future increase in stratospheric H 2 O are a rise in tropospheric CH 4 and H 2 leakages from an increased integration of hydrogen into the energy supply system. Here we evaluate the impact of potential future stratospheric H 2 O increases on Arctic ozone loss by comparing ozone loss proxies based on two different mechanisms of chlorine activation. In particular, the H 2 O dependence of the volume of air is analyzed where temperatures are low enough to form nitric acid trihydrate, denoted as V PSC , and for Cl activation on liquid sulfate aerosols, denoted as V ACl . We show that V ACl increases faster than V PSC with increasing H 2 O mixing ratios in the altitude range of 400 K to 550 K potential temperature. As a consequence, the additional ozone column loss is expected to be most pronounced for cold winters and large H 2 O increases and to be significantly higher when V ACl is used as a proxy.