Understanding the relation between Arctic ozone loss and the volume of polar stratospheric clouds

Abstract

A relationship between Arctic ozone loss and the volume of polar stratospheric clouds (PSCs) has been observed. This is shown to still hold when updated through the 2007/08 Arctic winter. The surprising and to-date unexplained qualities of this relationship are its compactness and its near-linearity, and we examine this relationship by calculating the chemical evolution along idealized trajectories using a photochemical box model. The rate-determining step for activation in the early part of the winter is the photolysis of J(HNO₃) as that limits the supply of ClONO₂ which reacts rapidly with HCl on PSCs. As a result the timescale for activation is weeks. The extent of activation thus depends on the continued presence of PSCs and hence on the time integral of the volume of the PSCs. During the subsequent ozone loss period, the ozone loss is found to depend on the competition between the photolysis of ClOOCl (leading to ozone loss) and the photolysis of HNO₃ (leading to deactivation). Both processes accelerate as the solar zenith angle decreases, and we find that the integrated amount of ozone loss depends primarily on the extent of the initial chlorine activation and not on the speed of the ozone loss.

Acknowledgments

Meteorological data were provided by ECMWF and FU-Berlin. This work was supported by the EU Integrated Project SCOUT-O3 (505390-GOCE-CT-2004) and by the BMBF DYCHO project (FKZ07ATC08). We thank the many ozonesonde personnel who have launched the ozonesondes used in this analysis.