Measurement report: Molecular characteristics of cloud water in southern China and insights into aqueous-phase processes from Fourier Transform Ion Cyclotron Resonance Mass Spectrometry
- 1State Key Laboratory of Organic Geochemistry and Guangdong Key Laboratory of Environmental Protection and Resources Utilization, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, 510640, PR China
- 2University of Chinese Academy of Sciences, Beijing, 100049, PR China
- 3Guangdong-Hong Kong-Macao Joint Laboratory for Environmental Pollution and Control, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, PR China
- 4State Environmental Protection Key Laboratory of Regional Air Quality Monitoring, Guangdong Environmental Monitoring Center, Guangzhou 510308, PR China
- 5Shanghai Key Laboratory of Atmospheric Particle Pollution and Prevention, Department of Environmental Science and Engineering, Fudan University, Shanghai 200433, PR China
- 6Shaoguan Environmental Monitoring Center, Shaoguan 512026, PR China
- anow at: Institute of Meteorology and Climate Research, Karlsruhe Institute of Technology, Eggenstein-Leopoldshafen 76344, Germany
- bnow at: Institute of Mass Spectrometry and Atmospheric Environment, Guangdong Provincial Engineering Research Center for On-line Source Apportionment System of Air Pollution, Jinan University, Guangzhou 510632, PR China
Abstract. Characterizing the molecular composition of cloud water could provide unique insight into the aqueous chemistry. Field measurement was conducted at Mt. Tianjing in southern China during May, 2018. Thousands of formulas (C5-30H4-55O1-15N0-2S0-2) were identified in cloud water by Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS). CHON represents the dominant component (43.6–65.3 % of relative abundance), followed by CHO (13.8–52.1 %). S-containing formulas constitute the remaining ~10–20 %. Molecules have O/C of 0.45–0.56 and the double-bond equivalent of 5.10–5.70. More than 90 % are assigned as aliphatic and olefinic species. No statistical difference of oxidation state is observed between cloud water and interstitial PM2.5. CHON with aromatic structures are abundant in cloud water, suggesting their enhanced in-cloud formation. Other organics in cloud water are mainly from biomass burning and oxidation of biogenic volatile organic compounds. The cloud water contains more abundant CHON and CHOS at night, which are mainly contributed by –N2O5 function and organosulfates, demonstrating the enhanced formation in dark aqueous or multi-phase reactions. While more abundant CHO are observed during the daytime, likely due to the photochemical oxidation and photolysis of N-/S-containing formulas. The results provide an improved understanding on the in-cloud aqueous-phase reactions.
Wei Sun et al.
Wei Sun et al.
Wei Sun et al.
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