EVIDENCE FOR HBR PRODUCTION DUE TO MINOR CHANNEL BRANCHING AT MIDLATITUDES

Recently, Nolt et al. [1997] have presented HBr measurements over the height range 20-36 km. We have compared model calculations with these measurements and find definitive evidence for non-zero branching ratio s for HBr production from either HO2+BrO, k(1b); or OH+BrO, k(2b). For k(1b), best agreement between modelled and observed HBr concentration s is obtained if the branching ratio increases from similar to 0.4% at 20 km, to about 2% at 34 km with no additional contribution from the OH+BrO branch. However, a height-independent value of 1% also produces reasonable results. This branching ratio contradicts the study of Mel louki et al. [1994]. For OH+BrO, the best value of k(2b) appears to be 2-3%, if k(1a) = 0 which is comparable to the recently determined bra nching ratio for HCl production from the analogous chlorine reaction, OH+ClO.