Characteristics and major influencing factors of sulfate production via heterogeneous transition-metal-catalyzed oxidation during haze evolution in China

Özet

The heterogeneous transition-metal-catalyzed oxidation (hereinafter referred to as TMI-catalyzed pathway) is animportant pathway for atmospheric sulfate formation. While most research has focused on in-cloud reactions ofsulfate, studies on its heterogeneous reactions on aerosol surfaces remain scarce. To better understand thispathway, we investigated the temporal changes of sulfate heterogeneous production rates of this pathway duringhaze evolution, and did not find any pattern in different haze stages. Although previous studies have shown ahigh sensitivity of the TMI-catalyzed pathway to aerosol pH, sulfate production rates of this pathway did notalways increase in haze aggravation stages with higher aerosol acidity. We then explored the major influencingfactors on this pathway in various haze evolution stages. The results suggest that the highly variable dissolved Fe(III) and Mn(II) concentrations and ionic strength during haze evolution processes would considerably influencethe production rate of the TMI-catalyzed pathway. This further implies that the north or northwest air masses,which often carry crustal-source particulates, may have a non-negligible effect on sulfate formation during thegeneration and/or dissipation stages of haze in Beijing by influencing aerosol pH and transition-metal contents.