The role of sulfate and its corresponding S(IV)+NO2 formation pathway during the evolution of haze in Beijing

Fange Yue; Zhouqing Xie; Pengfei Zhang; Shaojie Song; Pengzhen He; Cheng Liu; Longquan Wang; Xiawei Yu; Hui Kang

doi:10.1016/j.scitotenv.2019.06.096

The role of sulfate and its corresponding S(IV)+NO₂ formation pathway during the evolution of haze in Beijing

Sci Total Environ. 2019 Oct 15:687:741-751. doi: 10.1016/j.scitotenv.2019.06.096. Epub 2019 Jun 13.

Authors

Fange Yue¹, Zhouqing Xie², Pengfei Zhang³, Shaojie Song⁴, Pengzhen He¹, Cheng Liu⁵, Longquan Wang¹, Xiawei Yu¹, Hui Kang¹

Affiliations

¹ Institute of Polar Environment & Anhui Key Laboratory of Polar Environment and Global Change, School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China.
² Institute of Polar Environment & Anhui Key Laboratory of Polar Environment and Global Change, School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China; Center for Excellence in Urban Atmospheric Environment, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen, Fujian 361021, China; Key Lab of Environmental Optics & Technology, Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei, 230031, China. Electronic address: zqxie@ustc.edu.cn.
³ School of Environmental Studies, China University of Geosciences, Wuhan 430074, China. Electronic address: zhangpf@cug.edu.cn.
⁴ School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA.
⁵ Institute of Polar Environment & Anhui Key Laboratory of Polar Environment and Global Change, School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China; Center for Excellence in Urban Atmospheric Environment, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen, Fujian 361021, China; Key Lab of Environmental Optics & Technology, Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei, 230031, China.

PMID: 31412477
DOI: 10.1016/j.scitotenv.2019.06.096

Abstract

To better understand the role of stationary sources during the evolution of haze, we investigated sulfate formation characteristics at different stages of four haze events in Beijing, China. The mass fraction of sulfate in PM_2.5 increased while that of nitrate declined slightly during the worsening process of most haze events, consistent with higher ratios of SO₄^2-/NO₃^- on haze days (0.50 on average) than those on clean days (0.32 on average). Further calculations indicated that sulfate had a higher mass growth rate than nitrate during the haze-worsening process, probably due to regional transport of sulfate from heavy industrial areas accompanied by increased sulfate secondary transformation during polluted periods. We quantitatively evaluated the contribution of the S(IV) + NO₂ reaction (pH-dependent) in sulfate formation during the haze evolution. The production rate (P_S(IV)+NO2) of the S(IV) + NO₂ pathway ranged from 1.97 × 10^-4 to 5.91 (mean: 0.39) μg·m^-3·h^-1. Its proportion to sulfate total heterogeneous production rate (P_S(IV)+NO2/P_het) was generally correlated positively with PM_2.5 concentrations, indicating the relative importance of this pathway on haze days. Due to the mutual restriction between aerosol pH and aerosol liquid water content (ALWC) during haze evolution, the relative contribution of the S(IV) + NO₂ pathway to sulfate heterogeneous formation was generally limited to 40%.

Keywords: Aerosol liquid water content; Aerosol pH; Haze evolution; Heterogeneous formation; Sulfate.