28 Jul 2023
 | 28 Jul 2023

Chemical composition, source and formation mechanism of urban PM2.5 in Southwest China

Junke Zhang, Yunfei Su, Chunying Chen, Wenkai Guo, Miao Feng, Danlin Song, Tao Jiang, Qiang Chen, Yuan Li, Wei Li, Yizhi Wang, Qinwen Tan, Ruohan Wu, Ruiyan Pu, Minhui Lu, Xuhui Shen, and Xiaojuan Huang

Abstract. Despite significant improvements in air quality in recent years, the Sichuan Basin (SCB) is still facing frequent haze pollution in winter. In this study, the chemical components of PM2.5 in a typical pollution period at the beginning of 2023 in Chengdu, a megacity in the SCB, were characterized by bulk-chemical and single-particle analysis, and the PM2.5 sources and formation mechanism of pollution were analyzed. The average mass concentration of PM2.5 during the study period was 95.4±29.7 μg m-3. Organic matter (OM) was the most abundant component (35.3 %), followed by nitrate (22.0 %), sulfate (9.2 %) and ammonium (7.8 %). The aerosol particles were classified into five categories: mineral, OM, S-rich, soot and fly ash/metal particles, and most of them were in the state of internal mixing. The entire observation period could be divided into two non-pollution periods (NP-1 and NP-2) and two haze periods (Haze-1 and Haze-2). With the evolution of pollution, the bulk-chemical and single-particle analysis exhibited similar characteristics, suggesting that Haze-1 was mainly caused by pollutants related to fossil fuel combustion, especially mobile sources, while Haze-2 was triggered by the rapidly increasing secondary pollutants. The PM2.5 sources included dust (8.5 %), biomass burning (3.5 %), coal combustion (15.5 %), industrial processes (6.5 %), vehicular emissions (25.6 %) and secondary sources (40.5 %). Analysis of WRF-Chem model results showed that the average contributions of local sources and regional transmission to pollution in Chengdu were the same (50 % vs 50 %). In addition, the source composition and WRF-Chem simulation results in different periods confirmed our analysis of the formation mechanisms of the two haze events.

This study confirms that, despite the significant reduction in pollution experienced by Chengdu in the past decade, further significant reductions in PM2.5 are still needed, with particular emphasis on vehicular emissions and secondary sources. High intensity local emissions or large amounts of regional transmission may cause serious haze events, and more effective policies for local emissions reduction or joint prevention and control of regional air pollution are necessary in the future.

Junke Zhang et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse

Junke Zhang et al.


Total article views: 476 (including HTML, PDF, and XML)
HTML PDF XML Total Supplement BibTeX EndNote
340 116 20 476 37 5 12
  • HTML: 340
  • PDF: 116
  • XML: 20
  • Total: 476
  • Supplement: 37
  • BibTeX: 5
  • EndNote: 12
Views and downloads (calculated since 28 Jul 2023)
Cumulative views and downloads (calculated since 28 Jul 2023)

Viewed (geographical distribution)

Total article views: 466 (including HTML, PDF, and XML) Thereof 466 with geography defined and 0 with unknown origin.
Country # Views %
  • 1
Latest update: 10 Dec 2023
Short summary
Despite significant improvements in air quality in recent years, Chengdu is still facing frequent haze pollution in winter and its formation mechanism is still not clear enough. We analyzed the typical pollution process that occurred in early 2023 by combining two different perspectives of chemical component determination results, source analysis results and model simulation results. We found that that the joint prevention and control of regional air pollution is still necessary for Chengdu.