4.7 Article

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

Journal

ENVIRONMENTAL POLLUTION
Volume 312, Issue -, Pages -

Publisher

ELSEVIER SCI LTD
DOI: 10.1016/j.envpol.2022.119988

Keywords

Aerosol; Gaseous pollutant; Regional transport; Vertical profile; Flux

Funding

  1. National Natural Science Foundation of China [41977184, U21A2027]
  2. Strategic Priority Research Program of the Chinese Academy of Sciences [XDA23020301]
  3. Key Research and Development Project of Anhui Province [202104i07020002]
  4. Major Projects of High Resolution Earth Observation Systems of National Science and Technology [05-Y30B01-9001-19/20-3]
  5. Youth Innovation Promotion Association of CAS [2021443]
  6. Young Talent Project of the Center for Excel-lence in Regional Atmospheric Environment, CAS [CERAE202004]
  7. Cultivating Project of Strategic Priority Research Program of Chinese Academy of Sciences [XDPB1901]

Ask authors/readers for more resources

Previous studies have examined the influence of regional transport on aerosol pollution using numerical simulation or surface observation. However, vertical observations are necessary to fully understand regional transport due to the uneven vertical distribution of air pollutants. In this study, we used ground-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) to obtain the vertical profiles of aerosol and its precursors in suburban Beijing. We found that southwest-northeast transport had maximum net transport fluxes in the 200-300 m, 100-200 m, 500-600 m, and 500-600 m layers for aerosol extinction coefficient (AEC), NO2, SO2, and HCHO, respectively.
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 mu g 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 )m(2) 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 PM2.5 <75 mu g m(-3) and intense southwest transport dominated in polluted conditions with PM2.5 >75 mu g 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.

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