Atmos. Chem. Phys. Discuss., 9, 16163-16195, 2009
www.atmos-chem-phys-discuss.net/9/16163/2009/
doi:10.5194/acpd-9-16163-2009
© Author(s) 2009. This work is distributed
under the Creative Commons Attribution 3.0 License.
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
More evidence for very short-lived substance contribution to stratospheric chlorine inferred from HCl balloon-borne in situ measurements in the tropics
Y. Mébarki, V. Catoire, G. Berthet, N. Huret, and C. Robert
Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), UMR 6115 CNRS – Université d'Orléans, 45071 Orléans cedex 2, France

Abstract. Volume mixing ratio (vmr) vertical profiles of hydrogen chloride (HCl) are retrieved from in situ measurements performed by a balloon-borne infrared tunable diode laser absorption spectrometer (SPIRALE) during two balloon flights in the tropics (Teresina, Brazil, 5.1° S–42.9° W) at three year interval in June 2005 and June 2008. HCl vertical profiles obtained from 15.0 to 31.0 km are presented and analysed to estimate the contribution of very short-lived substances (VSLS) to total stratospheric chlorine. Both retrieved vertical profiles of HCl from these flights globally agree very well with each other, with estimated overall uncertainties of 6% on vmr between 23 and 31 km. Upper limits of HCl vmr as low as (20±20) pptv in June 2008 and (30±30) pptv in June 2005 are inferred in the upper part of the tropical tropopause layer (TTL). Backward trajectory calculations suggest that these low amounts were sampled in air masses corresponding to typical background conditions, i.e. neither influenced by recent tropospheric nor stratospheric air. Taking into account the recently reported VSLS source gas measurements obtained in similar conditions (Laube et al., 2008) and the main intermediate product gas (COCl2), a VSLS contribution of about (85±35 pptv) to total stratospheric chlorine is inferred. This refines the WMO (2007) estimation of 50 to 100 pptv, which was not taking into account any HCl contribution. In addition, comparisons of HCl measurements between SPIRALE and MLS-Aura satellite instrument in the tropical lower and middle stratosphere lead to a very good agreement. Since HCl modelled values derived from a total stratospheric chlorine budget including 100 pptv of VSLS agree with MLS measurements in the upper stratosphere, the consistency between SPIRALE and MLS measurements provides another evidence for this VSLS contribution.

Citation: Mébarki, Y., Catoire, V., Berthet, G., Huret, N., and Robert, C.: More evidence for very short-lived substance contribution to stratospheric chlorine inferred from HCl balloon-borne in situ measurements in the tropics, Atmos. Chem. Phys. Discuss., 9, 16163-16195, doi:10.5194/acpd-9-16163-2009, 2009.
 
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