Dark, Photolysis, and Oxidation Reaction Mechanism of Gaseous Dicarbonyls Based on PTR-TOF-MS

Dicarbonyls play a crucial role in the formation of atmospheric particles through complex physicochemical processes, while the mechanism is still unclear. This study investigated the dark, photolysis, and oxidation reactions of methylglyoxal (MG) and butanedione (BD) by using a proton-transfer-reaction time-of-flight mass spectrometry. A total of 11 or 10 gaseous products were detected in the initial MG or BD system, with acetaldehyde or acetone as the dominant product, exhibiting a concentration of 3.90 or 0.53 times that of gaseous MG or BD. Dark reaction increased the concentration of acetaldehyde by 95.91 ppb but decreased that of acetone by 3.15 ppb, and photolysis reaction further decreased the concentration of acetone by 4.75 times, while resulting in the concentration of acetaldehyde peaking at 106.78 ppb before decreasing to 17.34 ppb. “UV + OH” reaction rapidly decreased the concentrations of acetaldehyde and acetone, but quickly increased the concentration of acetic acid, which became the dominant product, accounting for >32%. Combined experimental data and Master Chemical Mechanism analysis revealed that dicarbonyls generated key acyl radicals, which then formed monocarbonyls that further polymerized into higher-mass oligomers. The findings provided direct evidence of the gas-phase reaction mechanism of dicarbonyls and offered important insights into their complex transformations in the atmospheric environment.