The reaction mechanism of SO with the multifunctional compound ethanolamine and its atmospheric implications.

SO is an important reactive species in sulfur cycle and sulfuric acid formation processes and its reactions with some functional group substances, such as HO, NH, CHOH, and organic and inorganic acids, have been extensively studied. However, its loss mechanism with multifunctional species is still lacking in detail. Herein, the reaction mechanism between SO and monoethanolamide (MEA) was investigated in the gas phase and on water droplets. The quantum chemical calculations indicate that the gas-phase reactions of SO with the OH and NH moieties of MEA hardly occur as their reaction energy barriers are up to 21.9-29.4 kcal mol. When a single water molecule is added into the SO + MEA reaction, it not only decreases the reaction barrier by at least 15.0 kcal mol and thus enhances the rate obviously, but can also lead to the main product changing from HOCHCHNHSOH to NHCHCHOSOH. The Born Oppenheimer molecular dynamics simulations on a water droplet show that the routes of the NHCHCHOSO⋯HO ion pair, HSO and HOCHCHNH ions and zwitterionic formations of HOCHCHNH-SO and SO-OCHCHNH occur through a loop-structure route or chain reaction process, and can be finished within several picoseconds. Interestingly, the nucleation simulations show that the products of HOCHCHNHSOH and NHCHCHOSOH have a potential ability to participate in the formation of new particles as they can form larger clusters with HSO, NH and HO molecules within 20 ns. Thus, the present study will not only give new insight into the reaction between SO and multifunctional compounds, but also provide a new potential formation mechanism for particles resulting from the loss of SO.