Reactions of OH radicals with dimethyl sulfoxide (CH3)2SO (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 N2 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) × 10-11 cm3 molecule-1 s-1 and k 2 = (9 ± 3) × 10-11 cm3 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.

Reactions of CH 3 SO radicals with O 3 and NO 2 have been studied at 140-660 Torr pressure of N 2 and 300 K using the pulsed laser photolysis technique with direct monitoring of SO 2 formation by laser induced fluorescence with excitation at 220.6 nm. The yield of SO 2 in the reaction of CH 3 SO with NO 2 has been found to be pressure dependent varying from (0.4 ( 0.12) at 100 Torr to (0.25 ( 0.05) at 664 Torr of N 2 . This result is in agreement with our previous data obtained using different experimental approach and may be interpreted by the formation of activated CH 3 SO 2 * radical followed by its prompt decomposition or collisional stabilization. The SO 2 yield in the reaction of CH 3 SO with O 3 has been found to be a factor (4.0 ( 0.3) higher than in the reaction with NO 2 corresponding to a yield of (1.0 ( 0.12) at 660 Torr of N 2 . The rate constant for the reactions CH 3 SO + O 3 , O + CH 3 SSCH 3 , and O + CS 2 at 300 K have been found to be (3.2 ( 0.9) × 10 -13 , (1.06 ( 0.07) × 10 -10 , and (3.6 ( 0.1) × 10 -12 cm 3 molecule -1 s -1 , respectively. The implications of the obtained results to the SO 2 yield in the atmospheric oxidation of dimethyl sulfide (DMS) are discussed. The results suggest that the CH 3 SO+O 3 reaction is a significant source of SO 2 in the mechanism of the DMS oxidation in the remote troposphere.