Current progress towards the heterogeneous reactions on mineral dust and soot

Haze is a phenomenon of visibility degradation caused by the extinction effects of atmospheric particulate matter (APM); these extinction effects are related to physicochemical properties of the aerosol particles. Therefore, the study of heterogeneous reactions on APM is relevant to establishing the formation mechanisms of haze. We review the latest research on heterogeneous reactions on mineral dust and soot particles. We discuss the effects of heterogeneous reactions on sources and sinks of trace gases, the formation of secondary aerosol, and the hygroscopic behavior of particles. We also summarize reactions relevant to haze formation. A synergistic effect occurs for coexisting gases involved in interface reactions. O2 plays a critical role in surface oxidation, while adsorbed organic species in soot support photo-oxidation. A number of important chemical reactions occur during humidification–dehumidification processes in mixed particles. Another relevant reaction mechanism is that weak acids replace strong acids. Finally, there is an enhancement effect of secondary aerosol on the hygroscopicity of APM. These results are not only useful for understanding heterogeneous reactions on APM, but also reveal some of the underlying mechanisms of haze formation in the coal producing areas of China.