Reactions of OH radicals with dimethyl sulfoxide (CH3)(2)SO (DMSO) (reaction 1) and methane sulfinic acid CH3S(O)OH (MSIA) (reaction 2) have been studied at 298 K and 200 and 400 Torr of N-2 using a newly constructed high-pressure turbulent flow reactor coupled to an ion molecule reaction mass spectrometer. The experimental setup is discussed in detail. The reactions of OH with DMSO and MSIA were found to proceed with predominant formation of MSIA and SO2, respectively. The yields of MSIA in reaction 1 and Of SO2 in reaction 2 were estimated to be 0.9 +/- 0.2. The reaction rate constants k(1) = (9 +/- 2) x 10(-11) cm(3) molecule(-1) s(-1) and k(2) = (9 +/- 3) x 10(-11) cm(3) molecule(-1) s(-1) were obtained. These results indicate that the OH-addition route of the gas-phase atmospheric oxidation of dimethyl sulfide, CH3SCH3 (DMS), which produces DMSO as a primary intermediate, would result in high yields Of SO2, which is a precursor of H2SO4. The results then suggest that the other major end product of DMS oxidation, methane sulfonic acid CH3SO3H (MSA), would not be produced by gas-phase reactions involving MSIA as suggested so far, but rather by liquid-phase reactions.