Column amounts of ClONO2, HCl, HNO3, and HF from ground-based FTIR measurements made near Kiruna, Sweden, in late winter 1994

During SESAME phase I ground-based FTIR measurements were performed at Esrange near Kiruna, Sweden, from 28 January to 26 March 1994. Zenith column amounts of ClONO2, HCl, HF, HNO3, O-3, N2O, CH4, and CFC-12 were derived from solar absorption spectra, Time series of ClONO2 and HCl indicate a chlorine activation at the end of January and around 1 March. On 1 March a very low amount of HCl of 2.09 x 10(15) molec. cm(-2) was detected, probably caused by a second chlorine activation phase starting from an already decreased amount of HCl. The ratio of column amounts of HCl to ClONO2 decreased inside the vortex from about 1 in January to 0.4 in late March compared to values of about 2 outside the vortex. Although the Arctic stratosphere was rather warm in winter 1993/94 and PSCs occurred seldom, chlorine partitioning into its reservoir species HCl and ClONO2 changed during that winter and ClONO2 is the major chlorine reservoir at the end of the winter as in cold winters like 1991/92 and 1994/95.