Uptake measurements of dibasic esters by water droplets and determination of their Henry's law constants

The uptake of dimethyl malonate and dimethyl succinate on aqueous surfaces was measured between 266 and 279 K, using the droplet train technique coupled with mass spectrometric detection. The uptake coefficients gamma were found to be independent of the aqueous phase composition and of the gas-liquid contact times. In addition, the uptake coefficients and the derived mass accommodation coefficients a show a negative temperature dependence in the temperature ranges studied. The mass accommodations decrease from 7.8 x 10(-2) to 5.0 x 10(-2) and from 4.5 x 10(-1) to 2.3 x 10(-2) for dimethyl malonate and succinate, respectively. These results are used to discuss the incorporation of oxygenated volatile organic compounds (VOCs) into the liquid using the nucleation theory. Henry's law constants of both compounds were directly measured between 283 and 298 K using a dynamic equilibrium system. Their values exponentially decrease when temperature increases, from (2.60 +/- 0.30) x 10(4) to (0.40 +/- 0.05) x 10(4) and from (1.20 +/- 0.10) x 10(4) to (0.30 +/- 0.03) x 10(4) for dimethyl malonate and succinate, respectively (in units of M atm(-1)). The partitioning of both dibasic esters between gas and aqueous phases and the corresponding atmospheric lifetimes have then been derived.