Motivated by the recent observations of springtime ozone loss in the Arctic boundary layer, we have studied the heterogeneous reactions HOBr+HBr→Br2+H2O and HOBr+HCl→BrCl+H2O using a low temperature flow tube coupled to a mass spectrometer. By monitoring the decay of HOBr in an excess of either HBr or HCl, both reactions have been shown to occur readily on ice surfaces at 228 K with reaction probabilities of 0.12 (¿0.03) and 0.25 (+0.10/-0.05), respectively. The gas-phase reaction products, Br2 and BrCl, have been observed. Also, it has been shown that HOBr interacts strongly with supercooled 60 wt % sulfuric acid solutions, being taken up with a sticking coefficient of greater than 0.06. The atmospheric implications of the heterogeneous reactivity of HOBr and HBr are discussed.