Atmos. Chem. Phys. Discuss., 5, 12939-12956, 2005
www.atmos-chem-phys-discuss.net/5/12939/2005/
doi:10.5194/acpd-5-12939-2005
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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.
Estimating the contribution of bromoform to stratospheric bromine and its relation to dehydration in the tropical tropopause layer
B.-M. Sinnhuber1 and I. Folkins2
1Institute of Environmental Physics, University of Bremen, Bremen, Germany
2Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia, Canada

Abstract. The contribution of bromoform to the stratospheric bromine loading is estimated using the one-dimensional tropical mean model of Folkins and Martin (2005), which is constrained by observed mean profiles of temperature and humidity. In order to reach the stratosphere, bromoform needs to be lifted by deep convection into the tropical tropopause layer (TTL), above the level of zero radiative heating. The contribution of bromoform to stratospheric bromine depends then critically on the rate of removal of the degradation products of bromoform (collectively called Bry here) from the TTL, which is believed to be due to scavenging by falling ice. This relates the transport of short-lived bromine species into the stratosphere to processes of dehydration in the TTL. In the extreme case of dehydration occurring only through overshooting deep convection, the loss of Bry from the TTL may be negligible and consequently bromoform will fully contribute with its boundary layer mixing ratio to the stratospheric bromine loading, i.e. with 3 pptv for an assumed 1 pptv of bromoform in the boundary layer. For the other extreme that Bry is removed from the TTL almost instantaneously, the model calculations predict a contribution of about 0.5 pptv for the assumed 1 pptv of boundary layer bromoform. While this gives some constraints on the contribution of bromoform to stratospheric bromine, it is argued that a more precise number cannot be given until the mechanisms of dehydration in the TTL are better understood.

Citation: Sinnhuber, B.-M. and Folkins, I.: Estimating the contribution of bromoform to stratospheric bromine and its relation to dehydration in the tropical tropopause layer, Atmos. Chem. Phys. Discuss., 5, 12939-12956, doi:10.5194/acpd-5-12939-2005, 2005.
 
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