Mechanism of the Reaction of CH₃SO with NO₂in Relation to Atmospheric Oxidation of Dimethyl Sulfide:  Experimental and Theoretical Study

Abstract

CH 3 SO 2 radical decomposition and the mechanism of SO 2 and CH 3 formation in the reaction of CH 3 SO with NO 2 were experimentally investigated in the pressure range 1-612 Torr of He using laser pulsed photolysis/ laser-induced fluorescence and discharge flow mass spectrometry/laser-induced fluorescence techniques. The upper limit for the thermal decomposition rate of CH 3 SO 2 in the investigated pressure range has been found to be 100 s -1 at 300 K. High-pressure limit, k ∞ ) 2.08 × 10 3 s -1 , and low-pressure limit, k 0 ) 2.72 × 10 -17 cm 3 molecule -1 s -1 , of the rate coefficient of the CH 3 SO 2 decomposition have been derived from ab initio and RRKM calculations. The CH 3 SO 2 decomposition rate at 760 Torr and 300 K has been estimated to be about 200 s -1 from falloff calculations. Reaction of CH 3 SO with NO 2 has been found to form CH 3 and SO 2 with a yield varying from (0.33 ( 0.05) at 13 Torr to (0.18 ( 0.03) at 612 Torr of He. The rate constant for the reaction of CH 3 SO with NO 2 has been found to be (1.5 ( 0.4) × 10 -11 cm 3 molecule -1 s -1 at 300 K, independent of pressure. On the basis of ab initio and RRKM calculations, the experimental results have been interpreted by assuming the reaction of CH 3 SO with NO 2 to form chemically activated CH 3 SO 2 * radical followed by its thermal stabilization or prompt decomposition to CH 3 and SO 2 . The implication of the obtained results for the atmospheric oxidation of dimethyl sulfide is discussed.

Evaluated kinetic and photochemical data for atmospheric chemistry: Volume II – gas phase reactions of organic species

“…The preferred k ∞1 value is based on , Wollenhaupt and Crowley (2000), Martínez et al (2000) and Kukui et al (2000). Falloff curves are constructed with F c =0.44 from .…”

Modeling natural emissions in the Community Multiscale Air Quality (CMAQ) model – Part 2: Modifications for simulating natural emissions

“…A study by Kukui et al (2000) -published after Yin et al (1990) and Zaveri (1997), and too late to be included in the overview of Finlayson-Pitts and Pitts (2000) -examined in detail the issue of CH 3 SO 2 thermal decomposition. Kukui et al (2000) measured CH 3 SO 2 behavior and their data, coupled with theory, were used to develop a mathematical expression for CH 3 SO 2 thermal decomposition as a function of temperature and pressure.…”

“…Kukui et al (2000) measured CH 3 SO 2 behavior and their data, coupled with theory, were used to develop a mathematical expression for CH 3 SO 2 thermal decomposition as a function of temperature and pressure. This expression represents the CH 3 SO 2 loss rate throughout the troposphere for comparison with CH 3 SO 2 loss rates for its reactions with NO 2 , O 3 and HO 2 at realistic concentrations based on the rate constants used by Zaveri (1997).…”

Toward elimination of discrepancies between theory and experiment: The rate constant of the atmospheric conversion of SO 3 to H 2 SO 4

“…DMS is oxidized subsequently to SO 2 at a model frequency of 0.7 ϫ 10 to sulfur trioxide by reaction with the hydroxyl radical and O 2 (19)(20)(21)(22). Next, SO 3 is hydrated to form sulfuric acid (H 2 SO 4 ) and sulfates (SO 4 2Ϫ ), which play a major role in the process of cloud formation as good cloud condensation nuclei (23)(24)(25).…”