Sulfate formation is dominated by manganese-catalyzed oxidation of SO2 on aerosol surfaces during haze events

Weigang Wang,Yele Sun,Yunhong Zhang,Chaofan Lian,Mingyuan Liu,Junji Cao,Zhijie Li,Zhenying Xu,Tiantian Wang,Chuanwei Yan ,Guigang Tang,Hongyu Tian ,Tong Zhu,Weijun Li,Zhe Chen,Jingnan Hu,Li Zhou,Yu Song,Yuepeng Pan,Chao Peng,Maofa Ge

doi:10.1038/s41467-021-22091-6

Abstract

The formation mechanism of aerosol sulfate during wintertime haze events in China is still largely unknown. As companions, SO2 and transition metals are mainly emitted from coal combustion. Here, we argue that the transition metal-catalyzed oxidation of SO2 on aerosol surfaces could be the dominant sulfate formation pathway and investigate this hypothesis by integrating chamber experiments, numerical simulations and in-field observations. Our analysis shows that the contribution of the manganese-catalyzed oxidation of SO2 on aerosol surfaces is approximately one to two orders of magnitude larger than previously known routes, and contributes 69.2% ± 5.0% of the particulate sulfur production during haze events. This formation pathway could explain the missing source of sulfate and improve the understanding of atmospheric chemistry and climate change.

Highlights

The formation mechanism of aerosol sulfate during wintertime haze events in China is still largely unknown
Sulfate formation mechanisms primarily include the gas phase oxidation of SO2 by OH radicals and the aqueous oxidation of S(IV) by H2O2, O3, organic peroxides, and O2 catalyzed by transition metal ions (TMIs), e.g., Fe(III) and Mn(II), in cloud/fog water droplets[6]
The SO2 oxidation experiments were performed in a temperature and humidity-controlled chamber, which is described in detail in the “Methods” section (Supplementary Fig. 1)[29]

Summary

Introduction

The formation mechanism of aerosol sulfate during wintertime haze events in China is still largely unknown. Chemical transport model simulations show that the manganese-catalyzed oxidation of SO2 on aerosol surfaces dominates sulfate formation and contributes In our study, compared to the Mn-catalytic reaction, there was no noticeable sulfate formation observed through the Fe-catalytic pathway in the chamber experiment (Supplementary Fig. 3), and the reaction rate of the Fe–Mn-catalytic reaction did not show any synergism enhancement effect.

Results

Conclusion