A critical review of sulfate aerosol formation mechanisms during winter polluted periods

Sulfate aerosol contributes to particulate matter pollution and plays a key role in aerosol radiative forcing, impacting human health and climate change. Atmospheric models tend to substantially underestimate sulfate concentrations during haze episodes, indicating that there are still missing mechanisms not considered by the models. Despite recent good progress in understanding the missing sulfate sources, knowledge on different sulfate formation pathways during polluted periods still involves large uncertainties and the dominant mechanism is under heated debate, calling for more field, laboratory, and modeling work. Here, we review the traditional sulfate formation mechanisms in cloud water and also discuss the potential factors affecting multiphase S(IV) oxidation. Then recent progress in multiphase S(IV) oxidation mechanisms is summarized. Sulfate formation rates by different prevailing oxidation pathways under typical winter-haze conditions are also calculated and compared. Based on the literature reviewed, we put forward control of the atmospheric oxidation capacity as a means to abate sulfate aerosol pollution. Finally, we conclude with a concise set of research priorities for improving our understanding of sulfate formation mechanisms during polluted periods. (c) 2022 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V.

Automated summary

Sulfate aerosol has a significant impact on particulate matter pollution, human health, and climate change. Atmospheric models underestimate sulfate concentrations during haze episodes, indicating missing mechanisms. Despite progress in understanding sulfate sources, there are uncertainties in formation pathways during polluted periods, calling for more research. This review summarizes traditional sulfate formation mechanisms and discusses factors affecting multiphase S(IV) oxidation. It proposes controlling atmospheric oxidation capacity to mitigate sulfate aerosol pollution and provides research priorities for improving our understanding of sulfate formation mechanisms.