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 involved direct flow tube measurements of H₂SO₄ decay rates onto a polydisperse aerosol using chemical ionization mass spectroscopic detection. The aerosols of this study were partially hydrated crystalline salts with diameters in the size range of 20 to 400 nm. The mass accommodation coefficients, α, were calculated from the first-order rate constants for H₂SO₄ loss to be 0.73 ± 0.21 and 0.79 ± 0.23 for loss onto (NH₄)₂SO₄ and NaCl, respectively. Measurements of the loss rate of H₂SO₄ onto a NaCl aerosol coated with stearic acid resulted in lower mass accommodation coefficients with values of 0.31 and 0.19 for aerosol with high and low stearic acid coverage, respectively. The observed decrease in α on an aerosol with a hydrocarbon coating suggests that aerosol composition is a key factor in H₂SO₄ adsorption on to a particle surface.