Volatile organosulfur compounds (VOSCs) in the atmosphere have attracted great interest because they play an important role in global warming, acid precipitation, and cloud formation (Bentley, R.; et al. Chemosphere 2004, 55, 291). Several studies have reported that high concentrations of VOSCs such as dipropyl thiosulfinate (DPTS) are emitted from various Allium genus plants such as garlic and onions that occupy large acreage on farmlands (Block, et al. J. Agric. Food Chem. 1992, 40, 2431). This raises the question of whether the farming of these crops and their emission of VOSCs into the atmosphere results in organosulfur “hotspots” that may contribute to global warming. Propanesulfinic acid (PSIA) is found to be an important intermediate in the atmospheric oxidation of DPTS (Arathala, P.; Musah, R. A. J. Phys. Chem. A 2020, 124, 8292) and its atmospheric fate is expected to be dominated by its reaction with OH radical. In this work, the atmospheric oxidation of PSIA with OH radical has been investigated at the CCSD(T)/aug-cc-pVTZ//M06-2X/aug-cc-pVTZ level. The reaction proceeds through: (i) H-atom abstraction; and (ii) OH radical addition pathways. The calculated energies suggest that abstraction of the H-atom from the -OH moiety of PSIA through a transition state with a barrier height of -4.7 kcal mol-1 relative to the separated reactants, leading to formation of CH3CH2CH2S(O)2 + H2O, is the major pathway. The rate coefficients were calculated for all possible pathways using Master equation solver for multi energy well reactions (Mesmer) code in the atmospheric temperature range 200-300 K and P = 0.1-10 atm. The total rate coefficient for the PSIA + OH reaction was found to be ~7.2 × 10-11 cm3 molecule-1 s-1 at T = 298 K and P = 1 atm. In addition, the thermochemistry, branching ratios, global warming potentials, and atmospheric implications for all paths were determined and are discussed.

Theoretical investigations on the atmospheric oxidation of propanesulfinic acid initiated by OH radical: Mechanism, energetics, kinetics, and atmospheric implications

ACS Spring Meeting 2021

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