Preprints
https://doi.org/10.5194/acp-2022-813
https://doi.org/10.5194/acp-2022-813
 
24 Jan 2023
24 Jan 2023
Status: this preprint is currently under review for the journal ACP.

Evolution and chemical characteristics of organic aerosols during wintertime PM2.5 episodes in Shanghai, China: Insights gained from online measurements of organic molecular markers

Shuhui Zhu1,2, Min Zhou1, Liping Qiao1, Dan Dan Huang1, Qiongqiong Wang3, Shan Wang2, Yaqin Gao1, Shengao Jing1, Qian Wang1, Hongli Wang1, Changhong Chen1, Cheng Huang1, and Jian Zhen Yu2,3 Shuhui Zhu et al.
  • 1State Environmental Protection Key Laboratory of the Cause and Prevention of Urban Air Pollution Complex, Shanghai Academy of Environmental Sciences, Shanghai, China
  • 2Division of Environment and Sustainability, Hong Kong University of Science and Technology, Hong Kong, China
  • 3Department of Chemistry, Hong Kong University of Science and Technology, Hong Kong, China

Abstract. Organic aerosol (OA) is a significant part of urban fine particulate matter (PM2.5) and a lack of detailed knowledge of their sources has increasingly hindered the improvement of air quality in China in recent years as significant reductions have been achieved in inorganic ion constituents. In this study, a wide range of organic molecular markers in PM2.5 were monitored with a bihourly time resolution using a Thermal desorption Aerosol Gas chromatograph system (TAG) in urban Shanghai in winter 2019. The molecular marker data have provided a unique source tracking ability in characterizing the evolution of organic aerosols during nine wintertime episodic events. Episodes primarily influenced by local air masses were characterized with higher proportions and mass increments of secondary OA. Rapid elevation in both absolute mass concentration and relative proportion was observed for primary and secondary OA markers indicative of vehicle emissions (e.g., alkanes, hopanes, and 2,3-dihydroxy-4-oxopentanoic acid), as well as cooking activities (e.g., saturated and unsaturated fatty acids, and C9 acids). In comparison, episodes under significant influences of transported air mass were typically associated with a predominant PM2.5 contribution from secondary inorganic aerosols and enhanced OA contribution from biomass burning activities. The latter was evident from the tracer data (e.g., levoglucosan, aromatic polycarboxylic acids, and nitro-aromatic compounds). Secondary OA markers associated with later generation products of hydrocarbon oxidation process, such as C3–5 dicarboxylic acids, were the most deficient during local episodes while notably enhanced during the episodes under influence of transported air masses, reflecting different extent and pathways of atmospheric aging processing. The ability of distinguishing the variations of OA evolution during different types of episodes demonstrates the value of online organic molecular measurements to episodic analysis. The results indicate that control of local urban sources such as vehicular and cooking emissions would lessen severity of local episodes while regional control of precursors for secondary inorganic aerosols and biomass burning activities would reduce PM2.5 episodes under synoptic conditions conducive for regional transport.

Shuhui Zhu et al.

Status: open (until 07 Mar 2023)

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Shuhui Zhu et al.

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Short summary
Organic aerosol (OA) becomes increasingly important in urban PM2.5 pollution as inorganic ions are getting lower. We investigated chemical characteristics of OA during nine episodes in Shanghai. The unique availability of bi-hourly measured molecular markers revealed that control of local urban sources such as vehicular and cooking emissions would lessen severity of local episodes. Regional control of precursors and biomass burning would reduce PM2.5 episodes influenced by regional transport.
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