Study of the heterogeneous reaction of O3 with CH3SCH3

This work presents the heterogeneous kinetics of the reaction of CH 3 SCH 3 (dimethyl sulphide, DMS) with O 3 (ozone) in aqueous solution at different ionic strengths (0, 0.1 and 1.0 M NaCl) using the wetted-wall flowtube (WWFT) technique. Henry's law coefficients of DMS were determined on pure water and on different concentrations of NaCl 5 (0.1 M–4.0 M) in the WWFT from UV spectrophotometric measurements of DMS in the gas phase using a numerical transport model of phase exchange to be H (M atm −1) = 10 showing a significant effect of ionic strength, µ, on the solubility of DMS according to the equation ln H = −4061 T −1 + 0.052 µ 2 + 50.9 µ T −1 + 14.0. At concentrations of DMS (liq) above 50 µM, UV spectrophotometry of both O 3(gas) and DMS (gas) enables us to observe simultaneously the reactive uptake of O 3 on DMS solution and the gas-liquid equilibration of DMS along the flowtube. The uptake coefficient, γ, of O 3 on aqueous 15 solutions of DMS, varying between 1 and 15 · 10 −6 , showed a square root-dependence on the aqueous DMS concentration (as expected for diffusive penetration into the surface film, where the reaction takes place in aqueous solution). It was smaller on NaCl solution in accord with the lower solubility of O 3. The heterogeneous reaction of O 3(gas) with DMS (liq) was evaluated from the observations of the second order rate constant 20 (k II) for the homogeneous aqueous reaction O 3(liq) + DMS (liq) using a numerical model of radial diffusion and reactive penetration and leading to k II (in units of 10 8 M −1 s −1) = 4.1±1.2 at 291.0 K, 2.15±0.65 at 283.4 K and 1.8±0.5 at 274.4 K. Aside from the expected influence on solubility and aqueous-phase diffusion coefficient of both gases there was no significant effect of ionic strength on k II , that was determined for 0.