A MODEL STUDY OF THE POTENTIAL ROLE OF THE REACTION BRO+OH IN THE PRODUCTION OF STRATOSPHERIC HBR

We have used a constrained one-dimensional photochemical model to inve stigate the effect of a potential minor channel of the fast reaction b etween BrO + OH to produce HBr. There is no direct evidence for this r eaction but the analogous yield of HCl from ClO + OH is thought to be about 5%. With only a 1-2% yield of HBr the modelled HBr mixing ratio between 20-30 km increases from around 0.5 parts per 10(12) by volume (pptv) to 1-2 pptv. This brings the model into agreement with recent b alloon-borne observations of stratospheric HBr. Should BrO + OK produc e HBr with around 1-2% yield then this reaction will dominate HBr prod uction between 20-35 km. As the main loss of HBr is reaction with OH t his will lead to steady state HBr:BrO partitioning which is independen t of other species, and temperature.