Vertical profiles of the transport fluxes of aerosol and its precursors between Beijing and its southwest cities

Qihou Hu; Cheng Liu; Qihua Li; Ting Liu; Xiangguang Ji; Yizhi Zhu; Chengzhi Xing; Haoran Liu; Wei Tan; Meng Gao

doi:10.1016/j.envpol.2022.119988

Vertical profiles of the transport fluxes of aerosol and its precursors between Beijing and its southwest cities

Environ Pollut. 2022 Nov 1:312:119988. doi: 10.1016/j.envpol.2022.119988. Epub 2022 Aug 24.

Authors

Qihou Hu¹, Cheng Liu², Qihua Li³, Ting Liu⁴, Xiangguang Ji¹, Yizhi Zhu¹, Chengzhi Xing¹, Haoran Liu³, Wei Tan¹, Meng Gao⁵

Affiliations

¹ Key Laboratory of Environmental Optics and Technology, Anhui Institute of Optics and Fine Mechanics, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, 230031, China.
² Key Laboratory of Environmental Optics and Technology, Anhui Institute of Optics and Fine Mechanics, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, 230031, China; Center for Excellence in Regional Atmospheric Environment, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen, 361021, China; Department of Precision Machinery and Precision Instrumentation, University of Science and Technology of China, Hefei, 230026, China; Key Laboratory of Precision Scientific Instrumentation of Anhui Higher Education Institutes, University of Science and Technology of China, Hefei, 230026, China. Electronic address: chliu81@ustc.edu.cn.
³ Institute of Physical Science and Information Technology, Anhui University, China.
⁴ School of Earth and Space Sciences, University of Science and Technology of China, Hefei, 230026, China.
⁵ Department of Geography, State Key Laboratory of Environmental and Biological Analysis, Hong Kong Baptist University, Hong Kong, China.

PMID: 36028076
DOI: 10.1016/j.envpol.2022.119988

Abstract

The influence of regional transport on aerosol pollution has been explored in previous studies based on numerical simulation or surface observation. Nevertheless, owing to inhomogeneous vertical distribution of air pollutants, vertical observations should be conducted for a comprehensive understanding of regional transport. Here we obtained the vertical profiles of aerosol and its precursors using ground-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) at the Nancheng site in suburban Beijing on the southwest transport pathway of the Beijing-Tianjin-Hebei (BTH) region, China, and then estimated the vertical profiles of transport fluxes in the southwest-northeast direction. The maximum net transport fluxes per unit cross-sectional area, calculated as pollutant concentration multiply by wind speed, of aerosol extinction coefficient (AEC), NO₂, SO₂ and HCHO were 0.98 km^-1 m s^-1, 24, 14 and 8.0 μg m^-2 s^-1 from southwest to northeast, which occurred in the 200-300 m, 100-200 m, 500-600 m and 500-600 m layers, respectively, due to much higher pollutant concentrations during southwest transport than during northeast transport in these layers. The average net column transport fluxes were 1200 km^-1 m² s^-1, 38, 26 and 15 mg m^-1 s^-1 from southwest to northeast for AEC, NO₂, SO₂ and HCHO, respectively, in which the fluxes in the surface layer (0-100 m) accounted for only 2.3%-4.2%. Evaluation only based on surface observation would underestimate the influence of the transport from southwest cities to Beijing. Northeast or weak southwest transports dominated in clean conditions with PM_2.5 <75 μg m^-3 and intense southwest transport dominated in polluted conditions with PM_2.5 >75 μg m^-3. Southwest transport through the middle boundary layer was a trigger factor for aerosol pollution events in urban Beijing, because it not only directly bringing air pollutants, but also induced an inverse structure of aerosols, which resulted in stronger atmospheric stability and aggravated air pollution in urban Beijing.

Keywords: Aerosol; Flux; Gaseous pollutant; Regional transport; Vertical profile.

MeSH terms

Aerosols / analysis
Air Pollutants* / analysis
Air Pollution* / analysis
Beijing
China
Cities
Environmental Monitoring / methods
Nitrogen Dioxide / analysis
Particulate Matter / analysis

Substances

Aerosols
Air Pollutants
Particulate Matter
Nitrogen Dioxide