UPTAKE OF GAS-PHASE SULFUR SPECIES METHANESULFONIC-ACID, DIMETHYLSULFOXIDE, AND DIMETHYL SULFONE BY AQUEOUS SURFACES

Biogenic reduced sulfur species are emitted from the oceans and then oxidized in the marine boundary layer. The gas/liquid interactions of these oxidized species must be understood in order to evaluate the relative contributions to marine boundary layer aerosol levels from anthropogenic and biogenic sources and to assess the overall impact of these aerosols on global climate. A key parameter in understanding these interactions is the mass accommodation coefficient, which is simply the probability that a gas phase molecule enters into a liquid on striking the liquid surface. The mass accommodation coefficients for dimethylsulfoxide, dimethyl sulfone, and methanesulfonic acid into water have been measured as a function of temperature (260-280 K), pH (1-14), and NaCl concentration (0-3.5 M). The experimental method employs a monodispersed train of fast droplets in a low-pressure flow reactor. The mass accommodation coefficients show a negative temperature dependence varying from approximately 0.1 to approximately 0.2 over the range of temperatures studied. The measured uptake is independent of pH and NaCl concentration in the ranges studied. The mass accommodation coefficients are well expressed in terms of an observed Gibbs free energy DELTAG(obs)# = DELTAH(obs)# - TDELTAS(obs)# as alpha/(1 - alpha) = exp (-DELTAG(obs)#/RT). The results are discussed in terms of a previously described uptake model. In the marine boundary layer, mass transfer of these species into aerosols will be limited by mass accommodation for aerosols with diameters of less than 2 mum.