Mechanistic insights into Criegee intermediates with benzoic acid at gas-phase and air-water interface and nucleation of product

Since the detection of Criegee intermediates (CIs) in the gas phase, there has been a growing recognition of the important role of CIs in atmospheric oxidation. Further mechanistic investigations are required to fully elucidate the bimolecular reactions of CIs with atmospheric species, such as OH, RO2/HO2, and carbonyl compounds. This article primarily focused on the reactions of benzoic acid (BA) with syn- and anti- CH3CHOO (C2 CI) in both gas-phase and gas-liquid interface using density functional theory (DFT) and Born-Oppenheimer molecular dynamics (BOMD). The results reveal that the reactions of BA and anti-CH3CHOO represent the principal pathway in the gaseous phase, whereas the water-involved reactions exhibit higher energy barriers, rendering them less favorable for occurrence. At the air-water interface, the reactions of BA and C2 CI as well as the BA-catalyzed hydration take place on the picosecond scale, conforming to the stepwise mechanism. The direct reaction between BA and anti- CH3CHOO remains the main sink for C2 CI at the gas-liquid interface. Molecular dynamics (MD) simulations were employed to investigate the nucleation capabilities of the reaction products and to examine the influence of temperature and water molecules on the nucleation process. The product molecules of BA and C2 CI can form stable clusters with sulfuric acid, ammonia molecules, and water molecules within 30 ns? The nucleation ability tends to decrease with the elevation of temperature, and the presence of water molecules promotes the new particles formation (NPF). Therefore, BA and its products with CIs affect the budget of secondary organic aerosols (SOAs).