Ph.D. Thesis

Miriam von König: Chlorine activation and PSC-formation in the Arctic stratosphere

Abstract

Measurements of vertical profiles of the stratospheric trace gases ClO, HCl and HNO₃ are analysed and interpreted. The measurements were performed with the Airborne Submillimeter Radiometer ASUR during the Arctic winters 1998/1999 and 1999/2000. Special emphasis has been laid on the understanding of processes that are of importance for the formation of polar stratospheric cloud particles (PSCs) and the development of chlorine activation in the Arctic winter stratosphere which are the precursors of stratospheric ozone depletion.

Model studies of chlorine activation are performed for a case of temperatures just within the region of possible stratospheric cloud formation. The content of one polar stratospheric cloud is explored using the HNO₃ vapor pressure as an indicator of the particle composition. ASUR measurements of HCl, ClO and N₂O are used to calculate the stratospheric content of the most important chlorine species, such as the total inorganic chlorine Cl_y, the total activated chlorine ClO_x and the reservoir species HCl and ClONO₂. The evolution of chlorine activation and chlorine deactivation is examined throughout the very cold winter 1999/2000. This results are compared to model results of the 3-dimensional model SLIMCAT.

An important result of these investigations is that while in the very cold winter, the formation of activated chlorine ClO_x seems to be well understood, the chlorine activation in the comparatively warm periods is extremely difficult to model. This is due as well to a severe lack of knowledge considering the formation of solid particles in this temperature region as well as to the strong temperature dependance of chlorine activation on liquid particles.