Experimental Study of SO₂ Formation in the Reactions of CH₃SO Radical with NO₂ and O₃ in Relation with the Atmospheric Oxidation Mechanism of Dimethyl Sulfide

Abstract

Reactions of CH3SO radicals with O3 and NO2 have been studied at 140−660 Torr pressure of N2 and 300 K using the pulsed laser photolysis technique with direct monitoring of SO2 formation by laser induced fluorescence with excitation at 220.6 nm. The yield of SO2 in the reaction of CH3SO with NO2 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 N2. This result is in agreement with our previous data obtained using different experimental approach and may be interpreted by the formation of activated CH3SO2* radical followed by its prompt decomposition or collisional stabilization. The SO2 yield in the reaction of CH3SO with O3 has been found to be a factor (4.0 ± 0.3) higher than in the reaction with NO2 corresponding to a yield of (1.0 ± 0.12) at 660 Torr of N2. The rate constant for the reactions CH3SO + O3, O + CH3SSCH3, and O + CS2 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 cm3 molecule-1 s-1, respectively. The implications of the obtained results to the SO2 yield in the atmospheric oxidation of dimethyl sulfide (DMS) are discussed. The results suggest that the CH3SO+O3 reaction is a significant source of SO2 in the mechanism of the DMS oxidation in the remote troposphere.