Column measurements of stratospheric trace species over Åre, Sweden in the winter of 1991–1992

Total vertical column amounts of stratospheric HCl, HF, ClONO2 and HNO3 are reported from high resolution infrared solar absorption spectra taken during the European Arctic Stratospheric Ozone Experiment in the winter of 1991–1992. These ground based measurements were made near Åre in North Sweden (63.4°N, 13.1°E) at an altitude of 800 m using a Fourier transform spectrometer and tunable diode laser heterodyne spectrometer. On 9th January 1992 the HCl vertical column dropped to 1.2 × 1015 molecules cm−2 from a November average of 3.6 × 1015 molecules cm−2. The HCl drop occurred at a time when Åre was below the polar vortex and the lower stratospheric ClO column above Åre was elevated to ∼2 × 1015 molecules cm−2 as measured by the Microwave Limb Sounder experiment on the Upper Atmosphere Research Satellite. These measurements indicate conversion of lower stratospheric chlorine from reservoir to chemically active forms.