Gas-liquid interfacial reaction mechanisms of typical small α-dicarbonyls in the neutral and acidic droplets: Implications for secondary organic aerosol formation

Abstract

Small α-dicarbonyls (SαDs) are well-known as the important precursors of secondary organic aerosol (SOA). Hence, it is imperative to understand the atmospheric chemistry of SαDs to contribute to SOA formation. In this work, we investigated the interfacial chemistry of typical SαDs, including methylglyoxal (MG) and biacetyl (BA) in the neutral and acidic droplets by combined molecular dynamics and quantum chemical calculations. The trans configurations of MG and BA are found to be the favorable configurations at the interfaces and are prone to stay at the gas-liquid interface of the acidic droplet. The C=O group exhibits a preferential uptake orientation towards the interface because the carbonyl-O atom has a strong interaction with interfacial H₂O. The uptakes and accumulations of MG and BA at the interfaces are promoted by the acidic condition. Subsequent interfacial hydrations of MG and BA in the acidic droplet are beneficial to yield diols, which can engage in oligomerization in the droplet interior to contribute SOA formation. Our results provide the theoretical insight into the interfacial chemistry of SαDs and their role in SOA formation.