Mass accommodation coefficient of H2SO4 vapor on aqueous sulfuric acid surfaces and gaseous diffusion coefficient of H2SO4 in N-2/H2O

The experimental determination of the mass accommodation coefficient of H2S O4 vapor on aqueous sulfuric acid and the gas-phase diffusion coefficient o f H2SO4 vapor in N-2/H2O at 303 K is reported. The measurements were carrie d out under laminar flow conditions in a coated wall tubular flow reactor c oupled to a chemical ionization mass spectrometer for gas-phase detection. Wall loss rates of H2SO4 vapor, from which both the mass accommodation coef ficient and the gas diffusion coefficient were determined, were measured as a function of total reactor pressure, water vapor concentration, and sulfu ric acid vapor concentration. The observed wall loss rate coefficient depen ds 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 b ased on the additivity of kinetic resistances that couples gasphase diffusi on and mass accommodation to the measured H2SO4 vapor loss rate has been ap plied to the data. The model yields a lower limit of 0.43 with a best fit v alue of 0.65. The mass accommodation coefficient is independent of the liqu id H2SO4/H2O composition over the range investigated. The gas-phase diffusi on coefficient for H2SO4 vapor in N-2/H2O (H2O mixing ratio less than or eq ual to 0.32) was determined to be 66.8 +/- 1.1 Torr cm(2) s(-1). The resist ance model agrees well, with a more rigorous approximate solution to the fu ll continuity equation describing mass transport and kinetics. The atmosphe ric implications of the reported results are discussed.