HCl and ClO in activated Arctic air; first retrieved vertical profiles from TELIS submillimetre limb spectra

Abstract

Abstract. The first profile retrieval results of the Terahertz and submillimeter Limb Sounder (TELIS) balloon instrument are presented. The spectra are recorded during a 13-h balloon flight on 24 January 2010 from Kiruna, Sweden. The TELIS instrument was mounted on the MIPAS-B2 gondola and shared this platform with the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) and the mini-Differential Optical Absorption Spectroscopy (mini-DOAS) instruments. The flight took place within the Arctic vortex at an altitude of ≈34 km in chlorine activated air and both active (ClO) and inactive chlorine (HCl) have been measured over an altitude range of respectively ≈16–32 km and ≈10–32 km. In this altitude range, the increase of ClO concentration levels during sunrise have been recorded with a temporal resolution of one minute. During the daytime equilibrium a maximum ClO level of 2.1 ± 0.3 ppb has been observed at an altitude of 23.5 km. This equilibrium profile is validated against the ClO profile by the satellite instrument Microwave Limb Sounder (MLS) aboard EOS Aura. HCl profiles have been determined from two different isotopes – H35Cl and H37Cl – and are also validated against MLS. The precision of all profiles is well below 0.01 ppb and the overall accuracy is therefore governed by systematic effects. The total uncertainty of these effects is estimated to be maximal 0.3 ppb for ClO around its peak value at 23.5 km during the daytime equilibrium and for HCl it ranges from 0.05 to 0.4 ppb depending on altitude. In both cases the main uncertainty stems from a largely unknown non-linear response in the detector.