Uptake of BrONO2 onto bulk sulfuric acid solutions and submicron sulfuric acid aerosol particles was studied in laminar flow cylindrical reactors where a chemical ionization mass spectrometer was used to detect products and reactants. Results from measurements at low temperatures and for sulfuric acid content between 70 and 85 wt.% are presented. These measurements suggest that the reaction probability for BrONO2 on a given sulfuric acid solution does not depend strongly on temperature. The heterogeneous chemistry of HOBr, a product of the hydrolysis of BrONO2, was also studied on bulk sulfuric acid solutions (58--70 wt.%). Measurements of HOBr and HNO3 solubility and the reaction HOBr + HCl → BrCl + H2O are reported. Supplemented with previous measurements, a set of parameters to calculate the reaction probabilities appropriate to the stratosphere are deduced. These measurements confirm earlier assertions that the reaction can be a significant loss process for HCl when aerosol volume in the stratosphere is elevated.