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 coup led to a mass spectrometer. From these experiments, typical values for the quantity KD-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 liqui d phase diffusion coefficient, these measurements indicate that HBr is over 2 orders of magnitude more soluble in atmospheric sulfate aeroso ls than HCl. Similarly, HD1/2 for HOBr on 69.8 wt% sulfuric acid at 22 8 K has been measured to be 20 (M/atm)(cm(2)/s)(1/2), implying that HO Br, too, is highly soluble in sulfuric acid solutions. By exposing sul furic acid films simultaneously to HOBr and either HCl or HBr, the liq uid phase reactions HOBr + HCl --> BrCl + H2O and HOBr + HBr --> Br-2 + H2O have been studied. The results indicate that the HOBr/HCl hetero geneous reaction may play an important role in the activation of strat ospheric chlorine under volcanic aerosol conditions.