05 Aug 2022
05 Aug 2022
Status: this preprint is currently under review for the journal ACP.

Measurement report: Intensive biomass burning emissions and rapid nitrate formation drive severe haze formation in Sichuan basin, China: insights from aerosol mass spectrometry

Zhier Bao1, Xinyi Zhang1, Qing Li1, Jiawei Zhou1, Guangming Shi2, Li Zhou2, Fumo Yang2, Shaodong Xie3, Dan Zhang4, Chongzhi Zhai4, Zhenliang Li4, Chao Peng4, and Yang Chen1 Zhier Bao et al.
  • 1Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, Chongqing, 400714, China
  • 2Department of Environmental Science and Engineering, College of Architecture and Environment, Sichuan University, Chengdu 610065, China
  • 3SKL-ESPC and BIC-ESAT, College of Environmental Sciences and Engineering, Peking University, Beijing 100871, China
  • 4Academy of Environmental Science, Chongqing, 401147, China

Abstract. Haze pollution is a severe environmental problem, caused by elevation of fine particles (aerodynamic diameter < 2.5 μm, PM2.5), which is related to secondary aerosol formation, unfavourable synoptic conditions, regional transport, etc. The regional haze formation in basin areas, along with intensive emission of precursors, high relative humidity and poor dispersion conditions, is still limitedly understood.In this study, a field campaign was conducted to investigate the factors resulting in haze formation in Sichuan Basin (SCB) during winter in 2021. The fine aerosol chemical composition was characterised by using a time-of-flight aerosol chemical speciation monitor (ToF-ACSM) with the aim of inorganic and organic aerosol characterisation and source apportionment. The average concentration of non-refractory fine particles (NR-PM2.5) was 98.5 ± 38.7 μg/m3, and organics aerosols (OA), nitrate, sulphate, ammonium, and chloride occupied 40.3, 28.8, 10.6, 15.3 and 5.1 % of PM2.5. Three factors, including a hydrocarbon-like OA (HOA), a biomass burning OA (BBOA), and an oxygenated OA (OOA), were identified by applying the positive matrix factorisation (PMF) analysis, and they constituted 24.2, 24.2 and 51.6 % of OA on average, respectively. Nitrate formation was promoted by gas-phase and aqueous-phase oxidation, while sulphate was mainly formed through aqueous-phase. OOA showed strong dependence on Ox, demonstrating the contribution of photooxidation to OOA formation. OOA concentration increased as aerosol liquid water content (ALWC) increased within 200 μg/m3 and kept relatively constant when ALWC > 200 μg/m3, suggesting the insignificant effect of aqueous-phase reactions on OOA formation. Among the three haze episodes identified during the whole campaign, the driving factors were different: the first haze episode (H1) was driven by nitrate formation through photochemical and aqueous-phase reactions, and the second haze episode (H2) was mainly driven by the intense emission of primary organic aerosols from biomass burning and vehicle exhaust, while the third haze episode (H3) was mainly driven by reactions involving nitrate formation and biomass burning emission. HOA and BBOA were scavenged, while OOA, nitrate, and sulphate formation were enhanced by aqueous-phase reactions during fog periods, which resulted in the increase of O:C from pre-fog to post-fog periods. This study revealed the factors driving severe haze formation in SCB, and implied the benefit of controlling nitrate as well as intense biomass burning and vehicle exhaust emission to the mitigation of heavy aerosol pollution in this region.

Zhier Bao et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2022-477', Anonymous Referee #1, 30 Aug 2022
    • AC2: 'Reply on RC1', Yang Chen, 30 Nov 2022
  • RC2: 'Comment on acp-2022-477', Anonymous Referee #2, 02 Sep 2022
    • AC3: 'Reply on RC2', Yang Chen, 30 Nov 2022
  • AC1: 'Comment on acp-2022-477', Yang Chen, 28 Oct 2022

Zhier Bao et al.

Data sets

Chemical composition of PM2.5 for Deyang campaign Bao Zhi'er, Zhang Xinyi, Li Qing, Zhou Jiawei, Shi Guangming, Zhou Li, Yang Fumo, Xie Shaodong, Zhang Dan, Zhai Chongzhi, Li Zhenliang, Peng Chao, & Chen Yang

Zhier Bao et al.


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Short summary
We characterised no-refractory fine particulate matter (PM2.5) during winter in Sichuan Basin (SCB), southwest China. The factors driving severe aerosol pollution were revealed, highlighting the importance of rapid nitrate formation and intensive biomass burning. Nitrate was primarily formed through gas-phase oxidation during daytime and aqueous-phase oxidation during nighttime. Controlling nitrate and biomass burning will benefit the mitigation of haze formation in SCB.