Diffusion in sulfuric acid plays a role in heterogeneous stratospheric processes. Knowledge of diffusion coefficients is required to determine the partitioning of heterogeneous reactions between the bulk and the surface of sulfate aerosol particles. Diffusion coefficients are also needed to analyze time-dependent uptake data to obtain solubilities. In order to provide quantitatively accurate diffusion coefficients, the experimental challenges of measuring solute diffusion in strong electrolyte environments must be overcome. We use a modified diaphragm cell technique and report diffusion coefficients for HCl and HBr in sulfuric acid solutions from 220 to 300 K. We find that the temperature and viscosity dependence of these measurements follows the equation D=cT/&eegr;, where &eegr; is viscosity, yielding c=7.8¿10-8 cm2 cP/s K for HCl and c=7.9¿10-8 cm2 cP/s K for HBr. An empirical equation for predicting diffusion coefficients for other species in sulfuric acid is also presented. ¿ 1998 American Geophysical Union