The kinetics and mechanism of the thermal decomposition of CH3SO2 and its reaction with NO2 have been investigated in a discharge flow reactor at 298 K and 1 Torr pressure using Cl/Cl-2/CH3SH/NO2/He mixtures : CH3SO2 + NO2 --> CH3SO3 + NO (3); CH3SO2 + M --> CH3 + SO2 + M (4). The rate constants k(3) and k(4) were derived from the fitting of calculated and experimental kinetic profiles of CH3O and SO2 monitored by laser-induced fluorescence (LIF) analysis. CH3 produced in reaction 4 was rapidly converted into CH3O by reaction with NO2. The values obtained were k(3) = (2.2 +/- 1.1) x 10(-12) cm(3) molecule(-1) s(-1) and k(4) = 510 +/- 150 s(-1). Errors are 1 standard deviation. The role of these reactions in the atmospheric oxidation mechanism of dimethyl sulfide is discussed.