April 1993 Arctic profiles of stratospheric HCl, ClONO2, and CCl2F2 from atmospheric trace molecule spectroscopy/ATLAS 2 infrared solar occultation spectra

Abstract

Partitioning among the major components of the stratospheric odd chlorine family inside and outside of the remanent Arctic vortex has been studied on the basis of infrared solar occultation measurements obtained by the atmospheric trace molecule spectroscopy (ATMOS) Fourier transform spectrometer during the ATLAS 2 shuttle mission (April 8–17, 1993). Profiles of hydrogen chloride (HCl) and simultaneous profiles of chlorine nitrate (ClONO2) and CFC‐12 (CCl2F2) are reported for examples of in‐vortex and out‐of‐vortex conditions. Increased ClONO2 volume‐mixing ratios (VMRs) are measured in the vortex below 20 mbar (∼25 km altitude) with a peak ClONO2 VMR of 2.05±0.45 ppbv (10−9 per volume) at 56 mbar (∼19 km altitude). The reported error correspond to 1σ uncertainties. Simultaneous CCl2F2 and N2O measurements, combined with published empirical relations, indicate that only 0.34±0.15 ppbv, about 10% of total chlorine, was bound in organic species at the ClONO2 VMR peak in the vortex. A colocated vortex profile of HCl, referenced to simultaneous N2O VMR measurements, has been used to derive a HCl mixing ratio of 1.21±0.12 ppbv corresponding to the ClONO2 VMR peak. The internal consistency of the ATMOS measurements is demonstrated by the agreement between the total chlorine mixing ratio of 3.60±0.72 ppbv derived at the ClONO2 VMR peak in the vortex and HCl measurements of 3.37±0.37 and 3.76±0.41 ppbv at 0.56 mbar, where HCl is the only significant chlorine‐bearing molecule. Outside the vortex the mixing ratio of HCl exceeds the mixing ratio of ClONO2 throughout the stratosphere.