The first-order loss rate coefficients for BrONO2 on 45, 60, and 70 wt % sulfuric acid solutions were measured in a wettted-wall flow tube reactor. The BrONO2 reactive uptake coefficients were >0.2 and HOBr was the product. When HCl was added to the acid, production of HOBr was still observed but the main product was BrCl. Based on these observations it is concluded that the conversion of BrONO2 to active forms such as HOBr and BrCl on sulfate aerosols in the stratosphere is very rapid. The efficiency of the hydrolysis of BrONO2 suggests that, even for nonvolcanic conditions, much of the BrONO2 in the stratosphere can be converted to HOBr at night. ¿ American Geophysical Union 1995