First direct simultaneous HCl and ClONO2 profile measurements in the Arctic vortex

Abstract

Coincident vertical profiles of HCl and ClONO2 in the Arctic vortex have been retrieved simultaneously in the altitude range 13 to 31 km. Solar occultation spectra were recorded, during both ascent and occultation, with a balloon-borne infrared Fourier transform spectrometer launched on 22 March 1995 from Kiruna (Sweden, 67°N, 22°E). A depleted layer of HCl is observed between 16 and 18 km, whereas ClONO2 is showing values larger than 2 ppbv around 20 km. The impact on the derived total inorganic chlorine of a 20% increase of the current ClONO2 absolute line intensities is discussed. These first direct measurements of the mixing ratio profiles of HCl and ClONO2 are compared with the results of the REPROBUS chemistry transport model and discussed in term of chlorine partitioning.