Formation and Oxidation of Imidazole in Tropospheric Aqueous-Phase Chemistry: A Computational Study

Imidazole produced by the interaction of glyoxal with nitrogen-containing chemicals in atmospheric particles can yield secondary organic aerosol (SOA) due to atmospheric oxidation. However, knowledge about the aqueous phase reaction mechanism of imidazole formation and its oxidation is still very limited. This work investigated the formation mechanism and aqueous-phase oxidative degradation reactions of imidazole with the hydroxyl radical (^•OH), nitrate radical (NO₃^•), and ozone (O₃). Results showed that the formation of imidazole involves many dehydration reactions and is favorable under moderate- or low-RH conditions. The calculated atmospheric lifetimes of 14.05, 0.27, and 3.45 h for reactions with ^•OH, NO₃^•, and O₃, respectively, suggest the efficient oxidation of imidazole under tropospheric aqueous-phase conditions. Formamide and oxamide are the main products in the presence of O₂, and nitro-imidazoles can also be formed in the presence of NO₂. The optical properties of imidazole evolve significantly, attributable to the formation of nitro-imidazoles, resulting in a red shift of absorption peak to the UVA and UVB region.

Formamide and oxamide are the main aqueous oxidation products of imidazole, implying a potentially important source of SOA.