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Discussion papers
https://doi.org/10.5194/acp-2019-481
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2019-481
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 03 Jun 2019

Submitted as: research article | 03 Jun 2019

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This discussion paper is a preprint. A revision of this manuscript was accepted for the journal Atmospheric Chemistry and Physics (ACP) and is expected to appear here in due course.

Chemical characteristics of cloud water and the impacts on aerosol properties at a subtropical mountain site in Hong Kong

Tao Li1,2, Zhe Wang1, Yaru Wang1, Chen Wu1,2, Yiheng Liang1, Men Xia1, Chuan Yu1, Hui Yun1, Weihao Wang1, Yan Wang2, Jia Guo3, Hartmut Herrmann2,4, and Tao Wang1 Tao Li et al.
  • 1Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hong Kong, China
  • 2School of Environmental Science and Engineering, Shandong University, Qingdao 266237, China
  • 3Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
  • 4Leibniz Institute for Tropospheric Research (TROPOS), Permoserstrasse 15, 04318 Leipzig, Germany

Abstract. To investigate the cloud water chemistry and the effects of cloud processes on aerosol properties, comprehensive field observations of cloud water, aerosols, and gas-phase species were conducted at a mountaintop site in Hong Kong in October and November 2016. The chemical composition of cloud water including water-soluble ions, dissolved organic matter (DOM), carbonyl compounds, carboxylic acids, and trace metals was quantified. The measured cloud water was very acidic with a mean pH of 3.63, as the ammonium (174 μeq L−1) was insufficient for neutralizing the dominant sulfate (230 μeq L−1) and nitrate (160 μeq L−1). Substantial DOM was found in cloud water, with carbonyl compounds and carboxylic acids accounting for 18.2 % and 5.6 %, respectively. Different from previous observations, concentrations of methylglyoxal (19.1 μM) and glyoxal (6.72 μM) were higher than that of formaldehyde (1.59 μM). The partitioning of carbonyls between cloud water and the gas phase was also investigated. The measured aqueous fractions of dicarbonyls were comparable to the theoretical estimations, while significant aqueous-phase supersaturation was found for less soluble monocarbonyls, suggesting complicated effects of both physical and chemical processes. In-cloud oxidation played an important role in increasing DOM and sulfate in the cloud water. Abundant glyoxal is suggested to be the most likely precursor of cloud water organics. The aqueous formation of organics was enhanced by photochemistry and under less-acidic conditions. Moreover, as a result of the cloud processes, DOM mass fractions were found to be significantly elevated in in-cloud aerosols, which was likely to contribute to the increase in droplet-mode mass fraction of cloud processed aerosols. This study demonstrates the significant role of clouds in altering the chemical composition and physical properties of aerosols via scavenging and aqueous processes, and provides valuable information about aerosol–cloud interactions in subtropical and coastal regions.

Tao Li et al.
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Tao Li et al.
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Short summary
This work presents the field study of cloud water chemistry and interactions of cloud, gas and aerosols in the polluted coastal boundary layer in southern China. Substantial dissolved organic matters in the acidic cloud water were found, and the gas-aqueous partitioning of carbonyl compounds was investigated. The results demonstrated the significant roles of cloud processes in altering aerosol properties, especially in the formation of aqueous organics and droplet-mode aerosols.
This work presents the field study of cloud water chemistry and interactions of cloud, gas and...
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