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https://doi.org/10.5194/acp-2020-1123
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2020-1123
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  05 Nov 2020

05 Nov 2020

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This preprint is currently under review for the journal ACP.

The dynamic-thermal structures of the planetary boundary layer dominated by synoptic circulations and the regular effect on air pollution in Beijing

Yunyan Jiang1,2,, Jinyuan Xin1,2,3,, Ying Wang4, Guiqian Tang1, Yuxin Zhao3,5, Danjie Jia1,2, Dandan Zhao1,2, Meng Wang1, Lindong Dai1, Lili Wang1, Tianxue Wen1, and Fangkun Wu1 Yunyan Jiang 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
  • 3Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters, Nanjing University of Information Science & Technology, Nanjing, 210044, China
  • 4College of Atmospheric Sciences, Lanzhou University, Lanzhou 730000, China
  • 5Institude of Atmospheric Composition, Chinese Academy of Meteorological Science, Beijing 100081, China
  • These authors contributed equally to this work.

Abstract. Synoptic circulations play important roles in meteorological conditions and air quality within the planetary boundary layer (PBL). Based on Lamb-Jenkinson weather typing and multiple field measurements, this study reveals the mechanism of how the coupling effects of multiscale circulations influence PBL structure and pollution. Due to the topographic blocking in the daytime, pollutants accumulate in the plain areas horizontally. The sinking divergent flows overlying on the rising convergent flows within the PBL inhibit the continuously upward dispersion of aerosols vertically. At night, the horizontal and vertical coupling mechanisms synergistically worsen the pollution. The large-scale environmental winds and regional-scale breezes affect the pollution directly via the horizontal coupling effect, which generates a pollution convergent zone of different directional flows. The relative strength of flows causes the severely polluted area to move around horizontally from 39° N to 41° N. In addition, the multiscale circulations regulate the mixing and diffusion of pollutants indirectly via the vertical coupling effect, which changes the PBL dynamic-thermal structure. The warm advection transported by the upper environmental winds overlies the cold advection transported by the lower regional breezes, generating strong wind direction shear and advective inversion. The capping inversion and the convergent sinking motion within the PBL suppress massive pollutants below the zero speed zone. The multilayer PBL under cyclonic circulation has no diurnal variation. Weak ambient winds strengthen the mountain breezes observably at night, the temperature inversion can reach 900 m. The nocturnal shallower PBL, consistent with the zero velocity zone between ambient and mountain winds, can reach 600 m. By contrast, the PBL under southwesterly circulation is a mono-layer with obvious diurnal variation, reaching 2000 m in the daytime. The strong winds circulations restrain the development of regional breezes, the zero speed zone is located at 400 m and the inversion is lower than 200 m at night. The PBL under westerly circulation has a hybrid structure with both multiple aerosol layers and diurnal variation. The inversion is generated by the vertical shear of zonal winds. Clean and strong north winds are dominated under anticyclone circulation, the vertical shear and the diurnal variation of thermal field disappear because of strong turbulent mixing, and there is no significant PBL structure. Our results imply that the algorithm of atmospheric environmental capacity under synoptic circulations, such as the cyclonic type, with a multilayer PBL needs to be improved.

Yunyan Jiang et al.

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Short summary
The multiscale circulations coupling affect pollution by changing planetary boundary layer (PBL) structure. The multilayer PBL under cyclonic circulation has no diurnal variation, the temperature inversion and zero speed zone can reach 600 to 900 m with strong mountain winds. The monolayer PBL under southwest circulation can reach 2000 m, the inversion are lower than nocturnal PBL (400 m) with strong ambient winds. The vertical shear of zonal winds produce the inversion under west circulation.
The multiscale circulations coupling affect pollution by changing planetary boundary layer (PBL)...
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