MEASUREMENTS OF THE H2SO4 MASS ACCOMMODATION COEFFICIENT ONTO POLYDISPERSE AEROSOL

The loss rate of H2SO4 vapor onto submicron particles was measured for three different particle substrates. The experimental technique invol ved direct flow tube measurements of H2SO4 decay rates onto a polydisp erse aerosol using chemical ionization mass spectroscopic detection. T he aerosols of this study were partially hydrated crystalline salts wi th diameters in the size range of 20 to 400 nm. The mass accommodation coefficients, alpha, were calculated from the first-order rate consta nts for H2SO4 loss to be 0.73=/-0.21 and 0.79+/-0.23 for loss onto (NH 4)(2)SO4 and NaCl, respectively. Measurements of the loss rate of H2SO 4 onto a NaCl aerosol coated with stearic acid resulted in lower mass accommodation coefficients with values of 0.31 and 0.19 for aerosol wi th high and low stearic acid coverage, respectively. The observed decr ease in alpha on an aerosol with a hydrocarbon coating suggests that a erosol composition is a key factor in H2SO4 adsorption on to a particl e surface.