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https://doi.org/10.5194/acp-2019-966
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2019-966
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 17 Jan 2020

Submitted as: research article | 17 Jan 2020

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This preprint is currently under review for the journal ACP.

The haze pollution under strong atmospheric oxidization capacity in summer in Beijing: Insights into the formation mechanism of atmospheric physicochemical process

Dandan Zhao1,2,*, Guangjing Liu3,1,*, Jinyuan Xin1,2,4, Jiannong Quan5, Yuesi Wang1, Xin Wang3, Lindong Dai1, Wenkang Gao1, Guiqian Tang1, Bo Hu1, Yongxiang Ma1, Xiaoyan Wu1, Lili Wang1, Zirui Liu1, and Fangkun Wu1 Dandan Zhao et al.
  • 1State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry (LAPC), Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China
  • 2University of Chinese Academy of Sciences, Beijing 100049, China
  • 3College of Atmospheric Sciences, Lanzhou University, Lanzhou 730000, China
  • 4Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters, Nanjing University of Information Science and Technology, Nanjing 210044
  • 5Institute of Urban Meteorology, Chinese Meteorological Administration, Beijing, China
  • *These authors contributed equally to this study.

Abstract. Under strong atmospheric oxidization capacity, haze pollution in the summer of Beijing was the result of the synergistic effect of physicochemical process in the atmospheric boundary layer (ABL). The south/southwest areas generally ~ 60–300 km far away from Beijing were seriously polluted, in contrast to a clean situation in Beijing. The southerly winds moving more than ~ 20–30 km h−1 since early morning primarily caused the initiation of haze pollution. The PM2.5 level increased to 75 μg m−3 in several hours at daytime, which was simultaneously affected by the ABL structure. Additionally, the O3 concentration was quite high at daytime (250 μg m−3), corresponding to a strong atmospheric oxidation capacity. Numerous sulfate and nitrate were formed through active atmospheric chemical processes, with sulfur oxidation ratio (SOR) up to ~ 0.76 and nitrogen oxidation ratio (NOR) increasing from 0.09 to 0.26, which further facilitated the particulate matter (PM) level rising. Even so, the increase in sulfate was mainly linked by southerly transport. At midnight, the PM2.5 concentration sharply increased from 75 μg m−3 to 150 μg m−3 in 4 hours and stayed the highest level till the next morning. With the premise of an extremely stable ABL structure, the formation of secondary aerosols dominated by nitrate was quite intense, driving the outbreak of haze pollution. PM levels in the south/southeast of Beijing were significantly lower than that in Beijing over this time, even below air quality standards, thus, the contribution of pollution transport was almost gone. With the formation of nocturnal stable boundary layer of 0–0.3 km altitude, the extremely low turbulence kinetic energy (TKE) of 0–0.05 m2 s−2 inhibited the spread of particles and moisture, ending up with elevated levels of PM2.5 and relative humidity (~ 90 %) near the surface. Under quite high humidity and strong ambient oxidization capacity, the NOR rapidly increased from 0.26 to 0.60 and heterogeneous hydrolysis reactions at the moist particle surface were very significant. The nitrate concentration explosively increased from 11.6 μg m−3 to 57.8 μg m−3, while the concentrations of sulfate and organics slightly increased by 6.1 μg m−3 and 3.1 μg m−3, respectively. With clean & strong winds passing through Beijing, the stable ABL was broken with potential temperature gradient turning to negative and ABL heights increasing to ~ 2.5 km. The strong turbulence activity with TKE of ~ 3–5 m2 s−2 notably promoted the pollution diffusion. The self-cleaning capacity of the atmosphere is always responsible for the dispersion of air pollution. Even so, reducing atmospheric oxidization capacity such as strengthening the collaborative control of nitrogen oxide (NOx) and volatile organic compounds (VOCs) was urgent, as well as continuously deepening regional joint control of air pollution.

Dandan Zhao et al.

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Short summary
Under strong atmospheric oxidization capacity, haze pollution in the summer of Beijing was the result of the synergistic effect of physicochemical process in the atmospheric boundary layer (ABL). With the premise of an extremely stable ABL structure, the formation of secondary aerosols dominated by nitrate was quite intense, driving the outbreak of haze pollution.
Under strong atmospheric oxidization capacity, haze pollution in the summer of Beijing was the...
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