Interactions of HBr, HCl, and HOBr with supercooled sulfuric acid solutions of stratospheric composition

The time‐dependent uptakes of HBr and HCl by supercooled solutions of sulfuric acid have been studied using a low‐temperature flow tube coupled to a mass spectrometer. From these experiments, typical values for the quantity H * D 1/2 (where H * is the effective Henry's law constant and D is the liquid phase diffusion coefficient) have been measured to be 1100 and 3.3 (M/atm)(cm 2 /s) 1/2 for HBr and HCl, respectively, on 59.6 wt% sulfuric acid at 210 K. By estimating values for the liquid phase diffusion coefficient, these measurements indicate that HBr is over 2 orders of magnitude more soluble in atmospheric sulfate aerosols than HCl. Similarly, HD 1/2 for HOBr on 69.8 wt% sulfuric acid at 228 K has been measured to be 20 (M/atm)(cm 2 /s) 1/2 , implying that HOBr, too, is highly soluble in sulfuric acid solutions. By exposing sulfuric acid films simultaneously to HOBr and either HCl or HBr, the liquid phase reactions HOBr + HCl → BrCl + H 2 O and HOBr + HBr → Br 2 + H 2 O have been studied. The results indicate that the HOBr/HCl heterogeneous reaction may play an important role in the activation of stratospheric chlorine under volcanic aerosol conditions.