Aqueous reaction kinetics of ozone and dimethylsulfide and its atmospheric implications

Abstract

In order to understand and predict the budgets and distributions of ozone (O3) and dimethylsulfide (DMS) in the marine atmosphere, it is necessary to determine the rates of aqueous reactions in clouds and surface water that may influence the lifetimes of these species. We studied the kinetics of the aqueous phase reaction of O3 and DMS in the laboratory using a bubbler‐type gas‐liquid reactor at sub‐parts‐per‐billion (ppb) gas phase concentrations. The steady state reaction rate was determined from the decrease of gas phase DMS concentration in the effluent gas as ozone was simultaneously added. The reaction stoichiometry was found to be 1:1 with respect to the two reagents. Fitting the data to a kinetics scheme appropriate for a gas‐liquid reaction in the slow reaction regime where the reaction rate is governed by both chemical reaction and convective mass transfer, we determined an intrinsic second‐order aqueous rate coefficient of O3‐DMS reaction of 4×108(±40%) M−1 s−1 at 15.0°C. The implications of this reaction include (1) the atmospheric lifetime of DMS against in‐cloud O3‐DMS reaction at 30 ppb of O3 and 1 g m −3 liquid water concentration is calculated to be ∼3 days and is comparable to that against the gas phase reaction with OH radicals at 1×106 molecules cm−3; (2) the deposition of atmospheric O3 to the ocean surface is only slightly enhanced by the O3‐DMS reaction at the highest reported surface DMS concentrations, (∼40 nM); and (3) the sea to air flux of DMS is not affected by this reaction at O3 concentrations typical of the marine atmosphere.