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 o xidized in the marine boundary layer. The gas/liquid interactions of t hese oxidized species must be understood in order to evaluate the rela tive contributions to marine boundary layer aerosol levels from anthro pogenic and biogenic sources and to assess the overall impact of these aerosols on global climate. A key parameter in understanding these in teractions 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 dimethyls ulfoxide, dimethyl sulfone, and methanesulfonic acid into water have b een measured as a function of temperature (260-280 K), pH (1-14), and NaCl concentration (0-3.5 M). The experimental method employs a monodi spersed train of fast droplets in a low-pressure flow reactor. The mas s accommodation coefficients show a negative temperature dependence va rying from approximately 0.1 to approximately 0.2 over the range of te mperatures studied. The measured uptake is independent of pH and NaCl concentration in the ranges studied. The mass accommodation coefficien ts are well expressed in terms of an observed Gibbs free energy DELTAG (obs)# = DELTAH(obs)# - TDELTAS(obs)# as alpha/(1 - alpha) = exp (-DEL TAG(obs)#/RT). The results are discussed in terms of a previously desc ribed uptake model. In the marine boundary layer, mass transfer of the se species into aerosols will be limited by mass accommodation for aer osols with diameters of less than 2 mum.