The experimental determination of the mass accommodation coefficient of H2SO4 vapor on aqueous sulfuric acid and the gas-phase diffusion coefficient of H2SO4 vapor in N-2/H2O at 303 K is reported. The measurements were carried out under laminar flow conditions in a coated wall tubular flow reactor coupled to a chemical ionization mass spectrometer for gas-phase detection. Wall loss rates of H2SO4 vapor, from which both the mass accommodation coefficient and the gas diffusion coefficient were determined, were measured as a function of total reactor pressure, water vapor concentration, and sulfuric acid vapor concentration. The observed wall loss rate coefficient depends Linearly on the inverse of the total reactor pressure (0.54-10 Torr) and is independent of the aqueous sulfuric acid composition over the range 73-98 wt %, which was varied by the addition of water vapor. A kinetic model based on the additivity of kinetic resistances that couples gasphase diffusion and mass accommodation to the measured H2SO4 vapor loss rate has been applied to the data. The model yields a lower limit of 0.43 with a best fit value of 0.65. The mass accommodation coefficient is independent of the liquid H2SO4/H2O composition over the range investigated. The gas-phase diffusion coefficient for H2SO4 vapor in N-2/H2O (H2O mixing ratio less than or equal to 0.32) was determined to be 66.8 +/- 1.1 Torr cm(2) s(-1). The resistance model agrees well, with a more rigorous approximate solution to the full continuity equation describing mass transport and kinetics. The atmospheric implications of the reported results are discussed.