Preprints
https://doi.org/10.5194/acp-2022-573
https://doi.org/10.5194/acp-2022-573
 
29 Aug 2022
29 Aug 2022
Status: this preprint is currently under review for the journal ACP.

Multiple pathways for the formation of secondary organic aerosol in North China Plain in summer

Yifang Gu1,4, Ru-Jin Huang1,2,3,4, Jing Duan1, Wei Xu1, Chunshui Lin1, Haobin Zhong1,4, Ying Wang1, Haiyan Ni1, Quan Liu5, Ruiguang Xu6,7, Litao Wang6,7, and Yong Jie Li8 Yifang Gu et al.
  • 1SKLLQG, Center for Excellence in Quaternary Science and Global Change, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710061, China
  • 2Open Studio for Oceanic-Continental Climate and Environment Changes, Pilot National Laboratory for Marine Science and Technology (Qingdao), Qingdao 266000, China
  • 3Institute of Global Environmental Change, Xi'an Jiaotong University, Xi'an 710049, China
  • 4University of Chinese Academy of Sciences, Beijing 100049, China
  • 5State Key Laboratory of Severe Weather & Key Laboratory of Atmospheric Chemistry of C MA, Chinese Academy of Meteorological Sciences, Beijing 100081, China
  • 6Department of Environmental Engineering, School of Energy and Environmental Engineering, Hebei University of Engineering, Handan 056038, China
  • 7Hebei Key Laboratory of Air Pollution Cause and Impact, Handan 056038, China
  • 8Department of Civil and Environmental Engineering, and Centre for Regional Oceans, Faculty of Science and Technology, University of Macau, Taipa, Macau 999078, China

Abstract. Secondary organic aerosol (SOA) has been identified as a major contributor to fine particulate matter (PM2.5) in North China Plain (NCP). However, the chemical mechanisms involved are still unclear due to incomplete understanding of its multiple formation processes. Here we report field observations in summer in Handan of NCP, based on high-resolution online measurements. Our results reveal the formation of SOA via photochemistry and two types of aqueous-phase chemistry, the latter of which include nocturnal and daytime processing. The photochemical pathway is the most important under high Ox (=O3 + NO2) conditions (65.1 ± 20.4 ppb). The efficient SOA formation from photochemistry (phochem-SOA) dominated the daytime (65 % to OA) with an average growth rate of 0.8 μg m−3 h−1. During the high relative humidity (RH: 83.7 ± 12.5 %) period, strong nocturnal aqueous-phase SOA formation (aq-SOA) played a significant role in SOA production (45 % to OA) with a nighttime growth rate of 0.6 μg m-3 h-1. Meanwhile, an equally fast growth rate of 0.6 μg m-3 h-1 of phochem-SOA from daytime aqueous-phase photochemistry was also observed, which contributed 39 % to OA, showing that photochemistry in the aqueous phase is also a non-negligible pathway in summer. The primary-related-SOA (SOA attributed to primary particulate organics) and aq-SOA are related to residential coal combustion activities, supported by distinct fragments from polycyclic aromatic hydrocarbons (PAHs). Moreover, the conversion and rapidly oxidation of primary-related-SOA to aq-SOA could be possible in the aqueous phase under high-RH conditions. This work sheds light on the multiple formation pathways of SOA in ambient air of complex pollution, and improves our understanding of ambient SOA formation and aging in summer with high oxidation capacity.

Yifang Gu et al.

Status: open (until 15 Oct 2022)

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  • RC1: 'Comment on acp-2022-573', Anonymous Referee #1, 01 Oct 2022 reply

Yifang Gu et al.

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Short summary
Secondary organic aerosol (SOA) could be produced by various pathways but its formation mechanisms are unclear. Observations were conducted in North China Plain during a highly oxidizing atmosphere in summer. We found here that fast photochemistry dominated SOA formation during daytime. Two types of aqueous-phase chemistry (nocturnal and daytime processing) take place at high relative humidity. The potential transformation from primary organic aerosol (POA) to SOA was also an important pathway.
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