Sensitivity of Arctic ozone loss to stratospheric H₂O

[1] Likely causes of a future increase in stratospheric H₂O are a rise in tropospheric CH₄ and H₂ leakages from an increased integration of hydrogen into the energy supply system. Here we evaluate the impact of potential future stratospheric H₂O increases on Arctic ozone loss by comparing ozone loss proxies based on two different mechanisms of chlorine activation. In particular, the H₂O 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 H₂O 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 H₂O increases and to be significantly higher when V_ACl is used as a proxy.