Xianyu Yang1, Yaqiong Lu This email address is being protected from spambots. You need JavaScript enabled to view it.2, Xinsheng Zhu This email address is being protected from spambots. You need JavaScript enabled to view it.3, Jianjun He4, Qi Jiang5, Kai Wu1,6, Haolin Wang7, Xiaoling Zhang1, Shigong Wang1 

1 Plateau Atmosphere and Environment Key Laboratory of Sichuan Province, School of Atmospheric Sciences, Chengdu University of Information Technology, Chengdu, China
2 Institute of Mountain Hazards and Environment, Chinese Academy of Sciences, Chengdu, China
3 Nanjing Institute of Environmental Science, Nanjing, China
4 State Key Laboratory of Severe Weather and Key Laboratory of Atmospheric Chemistry of CMA, Chinese Academy of Meteorological Sciences, Beijing, China
5 Huangpi Meteorological Bureau of Wuhan, Wuhan, China
6 Department of Land, Air, and Water Resources, University of California, Davis, CA, USA
7 School of Atmospheric Sciences, Sun Yat-sen University, Zhuhai, Guangdong, China

Received: April 25, 2020
Revised: September 7, 2020
Accepted: October 4, 2020

 Copyright The Author's institutions. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are cited. 

Download Citation: ||https://doi.org/10.4209/aaqr.2020.04.0173  

Cite this article:

Yang, X., Lu, Y., Zhu, X., He, J., Jiang, Q., Wu, K., Wang, H., Zhang, X. and Wang, S. (2020). Formation and Evolution Mechanisms of Severe Haze Pollution in the Sichuan Basin, Southwest China. Aerosol Air Qual. Res. 20: 2557–2567. https://doi.org/10.4209/aaqr.2020.04.0173


  • The evolution mechanism of a severe haze episode in the Sichuan Basin was analyzed.
  • Transboundary transport plays an essential role in haze episodes in Sichuan Basin.
  • The horizontal transport process acts as a major source of PM2.5 in haze episode.


Severe haze episodes are important environmental issues, and the rapid formation and evolution mechanisms of such episodes over complex terrain remain poorly understood. The Sichuan Basin (SCB) periodically experienced heavy haze pollution during the winter of 2016, with the maximum regional average PM2.5 concentration reaching almost 120 µg m3. In this study, we characterize a severe haze episode in the SCB from 20 to 30 January 2017 using comprehensive measurements and model analyses. The evolution of this severe episode shows clear stages, with gradual PM2.5 increases under stagnant weather conditions in Stage I (aerosol accumulation stage) and with explosive PM2.5 increases mainly associated with cross-border transport from the southern SCB in Stage III (rapid formation stage). The process analysis results indicated that primary emissions and aerosol processes were the major sources of PM2.5 in these urban regions, whereas vertical transport and dry deposition generally acted as sinks of PM2.5. In the presence of southwesterly synoptic winds, the aerosols emitted from the southern SCB were transported to Chengdu and the surrounding areas through horizontal transport and accounted for 66% of the PM2.5 concentration in Chengdu during Stage III. Our results reveal the detailed formation mechanism of a severe haze episode in the SCB under the effects of regional transport and synoptic forcing patterns to improve the understanding of haze formation in areas with complex terrain.

Keywords: Air quality; Haze pollution; Process analysis; Sichuan Basin.

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