EXPERIMENTAL-DETERMINATION OF THE DIFFUSION-COEFFICIENT OF DIMETHYLSULFIDE IN WATER

Estimates of the sea-to-air flux of dimethylsulfide (DMS) are based on sea surface concentration measurements and gas exchange calculations. Such calculations are dependent on the diffusivity of DMS (D(DMS)), w hich has never been experimentally determined. In this study the diffu sivity of DMS in pure water was measured over a temperature range of 5 -degrees-30-degrees-C. The measurements were made using a dynamic diff usion cell in which the diffusing gas flows over one side of an agar g el membrane and the inert gas flows over the other side. The diffusion coefficient can be estimated from either time dependent or steady sta te analysis of the data, with an estimated uncertainty of less than 8% (1sigma) in each measurement. A best fit to all the experimental resu lts yields the equation D(DMS) (in cm2 sec - 1) = 0.020 exp (-18.1/RT) , where R = 8.314 x 10(-3) kJ mole-1 K-1 and T is temperature in kelvi n. The values of D(DMS) obtained in this study were 7-28% larger than estimates from the empirical formula of Hayduk and Laudie (1974) which has previously been used for DMS in gas exchange calculations. Applyi ng these values to seawater results in an increase of less than 5% in the global oceanic flux of DMS.