Various natural and anthropogenic sources are responsible for emission of a large number of volatile organosulfur compounds (VOSCs) into the atmosphere. These compounds contribute to the global sulfur budget, and also play important roles in global warming and acid rain production. Several studies have reported that Allium genus cash crops such as garlic and onions that occupy large acreage on farmlands throughout the world, emit high levels of VOSCs such as thiosulfinates into the atmosphere. 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 the sulfur budget and to global warming. In this work, we investigated the atmospheric oxidation of two major plant-derived thiosulfinates, dimethyl thiosulfinate (DMTS) and dipropyl thiosulfinate (DPTS) by OH and Cl radicals using high level quantum chemistry calculations. The reactions of DMTS+●OH/●Cl and DPTS+●OH/●Cl proceeds through: (i) abstraction; and (ii) substitution paths. The barrier heights for the possible H-abstraction and substitution paths indicate that addition of ●OH/●Cl to the sulfur atom of the sulfinyl group (S(=O)) group, followed by simultaneous cleavage of the S(=O)−S single bond, leading to the formation of propanethiyl radical (PTR) + propanesulfinic acid (PSIA), and PTR + propanesulfinyl chloride (PSICl), are the major pathways. The rate coefficients were calculated for all pathways associated with DMTS+●OH/●Cl and DPTS+●OH/●Cl using Master equation solver for multi energy well reactions (Mesmer) code in the atmospheric temperature range 200-300 K and P=1 atm. The total rate coefficient for the DMTS+●OH, DMTS+●Cl, DPTS+●OH, and DPTS+●Cl reactions were found to be 1.4×10-11, 3.7×10-11, 1.7×10-10, and 8.1×10-10 cm3 molecule-1 s-1 at T=298 K and P=1 atm. In addition, the thermochemistry, branching ratios, and global warming potentials were determined, and the atmospheric implications for all the reactions will be discussed.

Theoretical investigation of the reactions of plant-derived alkyl thiosulfinates with the OH and Cl radicals: Reaction mechanisms, energetics, kinetics, and atmospheric implications

Fall 2022 abstracts, posters, and presentations will launch in mid-September.

ACS Fall 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.