MASS-TRANSFER AT THE AIR-WATER-INTERFACE - MASS ACCOMMODATION COEFFICIENTS OF SO2, HNO3, NO2 AND NH3

We present here experimental determinations of mass accommodation coefficients beta using a low pressure tube reactor in which monodispersed droplets, generated by a vibrating orifice, are brought into contact with known amounts of trace gases. The uptake of the gases and the accommodation coefficient are determined by chemical analysis of the aqueous phase. We report in this article measurements of beta(exp) = (6.0 +/- 0.8) x 10(-2) at 298 K and with a total pressure of 38 Torr for SO2, (5.0 +/- 1.0) x 10(-2) at 297 K and total pressure of 52 Torr for HNO3, (1.5 +/- 0.6) x 10(-3) at 298 K and total pressure of 50 Torr for NO2, (2.4 +/- 1.0) x 10(-2) at 290 K and total pressure of 70 Torr for NH3. These values are corrected for mass transport limitations in the gas phase leading to beta = (1.3 +/- 0.1) x 10(-1) (298 K) for SO2, (1.1 +/- 0.1) X 10(-1) (298 K) for HNO3, (9.7 +/- 0.9) x 10(-2) (290 K) for NH3, (1.5 +/- 0.8) x 10(-3) (298 K) for NO3 but this last value should not be considered as the true value of beta for NO2 because of possible chemical interferences. Results are discussed in terms of experimental conditions which determine the presence of limitations on the mass transport rates of gaseous species into an aqueous phase, which permits the correction of the experimental values.