Preprints
https://doi.org/10.5194/acp-2021-953
https://doi.org/10.5194/acp-2021-953

  15 Dec 2021

15 Dec 2021

Review status: this preprint is currently under review for the journal ACP.

Chemical Transformation of α-Pinene derived Organosulfate via Heterogeneous OH Oxidation: Implications for Sources and Environmental Fates of Atmospheric Organosulfates

Rongshuang Xu1, Sze In Madeleine Ng1, Wing Sze Chow2, Yee Ka Wong3, Yuchen Wang2, Donger Lai1, Zhongping Yao4, Pui-Kin So4, Jian Zhen Yu2, and Man Nin Chan1,5 Rongshuang Xu et al.
  • 1Earth System Science Programme, Faculty of Science, The Chinese University of Hong Kong, Hong Kong, China
  • 2Department of Chemistry, The Hong Kong University of Science and Technology, Hong Kong, China
  • 3Division of Environment and Sustainability, The Hong Kong University of Science and Technology, Hong Kong, China
  • 4The University Research Facility in Life Sciences, The Hong Kong Polytechnic University, Hong Kong, China
  • 5The Institute of Environment, Energy, and Sustainability, The Chinese University of Hong Kong, Hong Kong, China

Abstract. Organosulfur compounds are found to be ubiquitous in atmospheric aerosols — a majority of which are expected to be organosulfates (OSs). Given the atmospheric abundance of OSs, and their potential to form a variety of reaction products upon ageing, it is imperative to study the transformation kinetics and chemistry of OSs to better elucidate their atmospheric fates and impacts. In this work, we investigated the chemical transformation of an α-pinene derived organosulfate (C10H17O5SNa, αpOS-249) through heterogeneous OH oxidation at a relative humidity of 50 % in an oxidation flow reactor (OFR). The aerosol-phase reaction products were characterized using the high-performance liquid chromatography-electrospray ionization-high resolution mass spectrometry and the ion chromatography. By monitoring the decay rates of αpOS-249, the effective heterogeneous OH reaction rate was measured to be (6.72 ± 0.55) × 10−13 cm3 molecule−1 s−1. This infers an atmospheric lifetime of about two weeks at an average OH concentration of 1.5 × 106 molecules cm–3. Product analysis shows that OH oxidation of αpOS-249 can yield more oxygenated OSs having a nominal mass-to-charge ratio (m/z) at 247 (C10H15O5S), 263 (C10H15O6S), 265 (C10H17O6S), 277 (C10H13O7S), 279 (C10H15O7S), and 281 (C10H17O7S). The formation of fragmentation products, including both small OSs (C < 10) and inorganic sulfates, is found to be insignificant. These observations suggest that functionalization reactions are likely the dominant processes and that multigenerational oxidation possibly leads to formation of products with one or two hydroxyl and carbonyl functional groups adding to αpOS-249. Furthermore, all product ions except m/z = 277 have been detected in laboratory generated α-pinene derived secondary organic aerosols as well as in atmospheric aerosols. Our results reveal that OSs freshly formed from the photochemical oxidation of α-pinene could react further to form OSs commonly detected in atmospheric aerosols through heterogeneous OH oxidation. Overall, this study provides more insights into the sources, transformation, and fate of atmospheric OSs.

Rongshuang Xu et al.

Status: open (until 26 Jan 2022)

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  • RC1: 'Comment on acp-2021-953', Anonymous Referee #1, 08 Jan 2022 reply

Rongshuang Xu et al.

Rongshuang Xu et al.

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Short summary
To date, while over a hundred organosulfates (OSs) have been detected in atmospheric aerosols, many of them are still unidentified, with unknown precursors and formation processes. We found the heterogeneous OH oxidation of an α-pinene derived organosulfate (C10H17O5SNa, αpOS-249) can proceed at an efficient rate and transform into more oxygenated OSs, which have been commonly detected in atmospheric aerosols and α-pinene derived SOA in chamber studies.
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