Multiple evaluations of atmospheric behavior between Criegee intermediates and HCHO: Gas-phase and air-water...

Given the high abundance of water in the atmosphere, the reaction of Criegee intermediates (CIs) with (H₂O)₂ is considered to be the predominant removal pathway for CIs. However, recent experimental findings reported that the reactions of CIs with organic acids and carbonyls are faster than expected. At the same time, the interface behavior between CIs and carbonyls has not been reported so far. Here, the gas-phase and air-water interface behavior between Criegee intermediates and HCHO were explored by adopting high-level quantum chemical calculations and Born-Oppenheimer molecular dynamics (BOMD) simulations. Quantum chemical calculations evidence that the gas-phase reactions of CIs + HCHO are submerged energy or low energy barriers processes. The rate ratios speculate that the HCHO could be not only a significant tropospheric scavenger of CIs, but also an inhibitor in the oxidizing ability of CIs on SO_x in dry and highly polluted areas with abundant HCHO concentration. The reactions of CH₂OO with HCHO at the droplet's surface follow a loop structure mechanism to produce i) SOZ (), ii) BHMP (HOCH₂OOCH₂OH), and iii) HMHP (HOCH₂OOH). Considering the harsh reaction conditions between CIs and HCHO at the interface (i.e., the two molecules must be sufficiently close to each other), the hydration of CIs is still their main atmospheric loss pathway. These results could help us get a better interpretation of the underlying CIs-aldehydes chemical processes in the global polluted urban atmospheres.