A comprehensive observation-based multiphase chemical model analysis of sulfur dioxide oxidations in both summer and winter

Huan Song,Huabin Dong,Mei Zheng,Keding Lu,Yuanhang Zhang,Limin Zeng,Min Hu,Shiyi Chen,Zhijun Wu,Shule Li,Can Ye

doi:10.5194/acp-21-13713-2021

Abstract

Abstract. Sulfate is one of the main components of haze fine particles, and its formation mechanism remains controversial. A lack of detailed and comprehensive field data hinders the accurate evaluation of relative roles of prevailing sulfate formation pathways. Here, we analyzed the sulfate production rates using a state-of-the-art multiphase model constrained to the observed concentrations of transition metal, nitrogen dioxide, ozone, hydrogen peroxide and other important parameters in winter and summer in the North China Plain. Our results showed that aqueous transition metal ion (TMI)-catalyzed oxidation was the most important pathway followed by the surface oxidation of Mn in both winter and summer while the hydroxyl and Criegee radical oxidations contribute significantly in summer. In addition, we also modeled the published cases for the fog and cloud conditions. It is found that nitrogen dioxide oxidation is the dominant pathway for the fog in a higher pH range while hydroperoxide and ozone oxidations dominated for the cloud.

Highlights

Secondary sulfate aerosols are an important component of fine particles in severe haze periods (Zheng et al, 2015; R.J. Huang et al, 2014; Guo et al, 2014), which adversely affect environmental quality and human health (Lippmann and Thurston, 1996; Fang et al, 2017; Shang et al, 2020)
We modeled the concentrations of the main reagents of sulfate formation reactions using a state-ofthe-art Peking University Multiple-phAse Reaction Kinetic (PKU-MARK) model based on the data measured in two field campaigns conducted in the winter and summer in the North China Plain (NCP) where several particle pollution episodes happened
Data points with relatively humidity (RH) smaller than 20 % and aerosol liquid water content (ALWC) smaller than 1 μg/m3 were abandoned to improve the accuracy of the results

Summary

Introduction

Secondary sulfate aerosols are an important component of fine particles in severe haze periods (Zheng et al, 2015; R.J. Huang et al, 2014; Guo et al, 2014), which adversely affect environmental quality and human health (Lippmann and Thurston, 1996; Fang et al, 2017; Shang et al, 2020). Multiphase oxidation of dissolved SO2 is more important than SO2 directly oxidized by gas-phase radicals (Atkinson et al, 2004; Barth et al, 2002) because of the significantly reduced ultraviolet (UV) radiation intensity due to the aerosol dimming effect. Rapid sulfate production is observed during cloud-free conditions, indicating that aerosol multiphase oxidation may be important during haze periods (Moch et al, 2018). These effects cause a major gap between the measured sulfate concentrations under weak UV radiation and the concentrations calculated using traditional atmospheric models

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Conclusion