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Discussion papers
https://doi.org/10.5194/acp-2019-245
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2019-245
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 28 Mar 2019

Submitted as: research article | 28 Mar 2019

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This discussion paper is a preprint. A revision of this manuscript was accepted for the journal Atmospheric Chemistry and Physics (ACP) and is expected to appear here in due course.

Assessing the formation and evolution mechanisms of severe haze pollution in Beijing−Tianjin−Hebei region by using process analysis

Lei Chen1,2, Jia Zhu1, Hong Liao1, Yi Gao3, Yulu Qiu4,5, Meigen Zhang3,6,7, and Nan Li1 Lei Chen et al.
  • 1Jiangsu Key Laboratory of Atmospheric Environment Monitoring and Pollution Control, Jiangsu Collaborative Innovation Center of Atmospheric Environment and Equipment Technology, School of Environmental Science and Engineering, Nanjing University of Information Science & Technology, Nanjing, 210044, China
  • 2Key Laboratory of Meteorological Disaster, Ministry of Education (KLME), Joint International Research Laboratory of Climate and Environment Change (ILCEC), Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters (CIC-FEMD), Nanjing University of Information Science & Technology, Nanjing, 210044, China
  • 3State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, 100029, China
  • 4Institute of Urban Meteorology, China Meteorological Administration, Beijing 100089, China
  • 5Beijing Shangdianzi Regional Atmosphere Watch Station, Beijing, China
  • 6University of Chinese Academy of Sciences, Beijing, 100049, China
  • 7Centerfor Excellence inRegionalAtmospheric Environment, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen, China

Abstract. Fine–particle pollution associated with haze threatens human health, especially in the North China Plain, where extremely high PM2.5 concentrations were frequently observed during winter. In this study, the WRF–Chem model coupled with an improved integrated process analysis scheme was used to investigate the formation and evolution mechanisms of a haze event happened over Beijing–Tianjin–Hebei (BTH) in December 2015, including examining the contributions of local emission and outside transport to the absolute PM2.5 concentration in BTH, and the contributions of each detailed physical or chemical process to the variations in the PM2.5 concentration. The influence mechanisms of aerosol radiative forcing (including aerosol direct and indirect effects) were also examined by using the process analysis. During the aerosol accumulation stage (December 20–22, Stage_1), the average near–surface PM2.5 concentration in BTH was 250.0 µg m−3, which was contributed by local emission of 42.3 % and outside transport of 36.6 %. During the aerosol dispersion stage (December 23–27, Stage_2), the average concentration of PM2.5 was 107.9 µg m−3. The contribution of local emission increased to 50.9 %, while the contribution of outside transport decreased to 24.3 %. The 24–h change (23:00LST minus 00:00LST) in the near–surface PM2.5 concentration was +50.4 µg m−3 during Stage_1 and −41.5 µg m−3 during Stage_2. Contributions of aerosol chemistry process and vertical mixing process to the 24–h change were +43.8 (+17.9) µg m−3 and −161.6 (−221.6) µg m−3 for Stage_1 (Stage_2), respectively. Small differences in contributions from other processes were found between Stage_1 and Stage_2, such as advection process, cloud chemistry process, and so on. Therefore, the PM2.5 increase over BTH during haze formation stage (Stage_1) was mainly attributed to strong production by aerosol chemistry process and weak removal by vertical mixing process. When aerosol radiative feedback was considered, the 24–h PM2.5 increase was enhanced by 9.6 µg m−3 during Stage_1, which could be mainly attributed to the contributions of vertical mixing process (+39.8 µg m−3), advection process (−38.6 µg m−3) and aerosol chemistry process (+5.1 µg m−3). The restrained vertical mixing could be the primary reason for the enhancement in near–surface PM2.5 increase when aerosol radiative forcing was considered.

Lei Chen et al.
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Short summary
The formation mechanism of a severe haze episode happened over North China in December 2015, and aerosol radiative impacts on the haze episode and the influence mechanism were examined. The PM2.5 increase during aerosol accumulation stage was mainly attributed to strong production by aerosol chemistry process and weak removal by vertical mixing process. The restrained vertical mixing could be the primary reason for near–surface PM2.5 increase when aerosol radiative feedback was considered.
The formation mechanism of a severe haze episode happened over North China in December 2015, and...
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