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Discussion papers
https://doi.org/10.5194/acp-2018-1189
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2018-1189
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 27 Nov 2018

Research article | 27 Nov 2018

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This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Modeling of aerosol property evolution during winter haze episodes over a megacity cluster in northern China: Roles of regional transport and heterogeneous reactions

Huiyun Du1,2, Jie Li1,2,3, Xueshun Chen1, Zifa Wang1,2,3, Yele Sun1,2,3, Pingqing Fu1, Jianjun Li4, Jian Gao5, and Ying Wei1,2 Huiyun Du et al.
  • 1LAPC, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China
  • 2College of Earth Sciences, University of Chinese Academy of Sciences, Beijing 100029, China
  • 3Center for Excellence in Urban Atmospheric Environment, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen, China
  • 4China National Environmental Monitoring Center, Beijing, China
  • 5Chinese Research Academy of Environmental Science

Abstract. Regional transport and heterogeneous reactions played crucial roles in haze formation over a megacity cluster centered on Beijing. In this study, the updated Nested Air Quality Prediction Model System (NAQPMS) and the HYSPLIT Lagrangian trajectory model were employed to investigate the evolution of aerosols – in terms of the number concentration, size distribution, and aging degree – in Beijing during six haze episodes between November 15 and December 15, 2016, as part of the Air Pollution and Human Health–Beijing (APHH-Beijing) winter campaign of 2016. The model exhibited reasonable performance not only for mass concentrations of PM2.5 and its components in Beijing but also for the number concentration, size distribution, and aging degree. We discovered that regional transport played a nonnegligible role in haze episodes, with contributions of 14%–31% to the surface PM2.5 mass concentration. The contribution of regional transport to secondary inorganic aerosols was larger than that of regional transport to primary aerosols (30%–63% vs. 3%–12%). The chemical transformation of SO2 in the transport pathway from source regions to Beijing was the major form of SO42− regional transport. We also found that sulfate formed outside Beijing from SO2 that was emitted in Beijing; this sulfate was then blown back to Beijing and considerably influenced haze formation. In the transport pathway, aerosols underwent aging, which altered the mass ratio of coating to black carbon (RBC) and the size distribution of number concentrations. During the episodes, the geometric mean diameter (GMD) increased from less than 100nm at the initial site to approximately 120nm at the final site (Beijing), and RBC increased from 2–4 to 4–8. These changes would affect regional radiation and climate. In haze episodes with high humidity, the average contributions of gas and aqueous chemistry, heterogeneous chemistry, and primary sulfate emission were comparable. Primary emissions had the greatest impact under light to moderate pollution levels, whereas heterogeneous chemistry had a stronger effect under high pollution levels.

Huiyun Du et al.
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Regional transport and heterogeneous reactions played crucial roles in haze formation. Using chemical transport model, we found that chemical transformation of SO2 in the transport pathway was the major form of sulfate regional transport. Heterogenous chemistry had a stronger effect under high humidity and high pollution levels. Aerosols underwent aging along transport which altered aerosol size and aging degree. These changes would affect regional radiation and climate.
Regional transport and heterogeneous reactions played crucial roles in haze formation. Using...
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