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Chemical transformation of a long-chain alkyl organosulfate via heterogeneous OH oxidation: a case study of sodium dodecyl sulfate

Ng, Sze In Madeleine and Ng, Kwan Hung and Yeung, Pui Wo Felix and Xu, Rongshuang and So, Pui-Kin and Huang, Yuanlong and Yu, Jian Zhen and Choi, Chun Kit K. and Tse, Ying-Lung Steve and Chan, Man Nin (2022) Chemical transformation of a long-chain alkyl organosulfate via heterogeneous OH oxidation: a case study of sodium dodecyl sulfate. Environmental Science: Atmospheres, 2 (5). pp. 1060-1075. ISSN 2634-3606. doi:10.1039/d2ea00026a.

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Organosulfates (OSs) are regarded as stable tracers of secondary organic aerosols. However, recent studies have reported their potential chemical instability, which is dependent on their structures. In this study, we aim to investigate the transformation and kinetics of a long-chain alkyl OS upon heterogeneous hydroxyl radical (OH) oxidation. We selected sodium dodecyl sulfate (SDS, C₁₂H₂₅O₄SNa) as a model compound due to its atmospheric relevance. We conducted experiments using an oxidation flow reactor at 80% RH and room temperature. We analyzed the reaction kinetics and products by liquid chromatography-mass spectrometry and ultrahigh-resolution mass spectrometry. We quantified inorganic sulfate formation by ion chromatography. We have proposed reaction pathways based on aerosol composition data. Our results reveal that dodecyl sulfate decays at (4.09 ± 0.09) × 10⁻¹³ cm³ per molecule per s with an atmospheric lifetime of ∼19 days upon heterogeneous OH oxidation. Compared with the literature results, we observe a significant kinetics enhancement when ammonium sulfate is present in aerosols. Our molecular dynamics simulations suggest that ammonium ions tend to displace sodium ions from the air–water interface and attract OH more strongly, which promotes collisions between dodecyl OS and OH. Therefore, the effects of counterions on surface-active organics should be considered during interpretation of experimental kinetics data. We detected sequential oxygenation of dodecyl sulfate, which dominated over fragmentation and inorganic sulfate formation. Our identified products indicate a potential source of some oxygenated aliphatic C₆- to C₁₀- and C₁₂-OS detected in the atmosphere. Collectively, our work highlights the need for more comprehensive investigations of structural factors governing OS chemistry.

Item Type:Article
Related URLs:
URLURL TypeDescription
Ng, Sze In Madeleine0000-0003-0919-2603
Yeung, Pui Wo Felix0000-0002-2897-5577
Huang, Yuanlong0000-0002-6726-8904
Yu, Jian Zhen0000-0002-6165-6500
Choi, Chun Kit K.0000-0003-1994-1719
Tse, Ying-Lung Steve0000-0003-1187-2296
Chan, Man Nin0000-0002-2384-2695
Additional Information:This work is supported by the Hong Kong Research Grants Council (HKRGC): Project ID 2130626 (Ref 14300118) and Project ID 2130705 (Ref 14300920). The authors are thankful for the support from the Li Ka Shing Foundation for ultrahigh-resolution Orbitrap Eclipse Tribrid mass spectrometry in the Li Ka Shing Translational Omics Platform.
Funding AgencyGrant Number
Research Grants Council of Hong Kong2130626
Research Grants Council of Hong Kong2130705
Issue or Number:5
Record Number:CaltechAUTHORS:20221003-756400000.29
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:117218
Deposited By: Melissa Ray
Deposited On:10 Oct 2022 13:52
Last Modified:10 Oct 2022 13:52

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