Huang Yuanlong, Barraza Kevin M, Kenseth Christopher M, Zhao Ran, Wang Chen, Beauchamp J L, Seinfeld John H
Division of Geological and Planetary Sciences , California Institute of Technology , Pasadena , California 91125 , United States.
Division of Chemistry and Chemical Engineering , California Institute of Technology , Pasadena , California 91125 , United States.
J Phys Chem A. 2018 Aug 9;122(31):6445-6456. doi: 10.1021/acs.jpca.8b05353. Epub 2018 Jul 30.
Gas and aqueous phases are essential media for atmospheric chemistry and aerosol formation. Numerous studies have focused on aqueous-phase reactions as well as coupled gas/aqueous-phase mass transport and reaction. Few studies have directly addressed processes occurring at the air-water interface, especially involving surface-active compounds. We report here the application of field-induced droplet ionization mass spectrometry (FIDI-MS) to chemical reactions occurring at the atmospheric air-water interface. We determine the air-water interfacial OH radical reaction rate constants for sodium dodecyl sulfate (SDS), a common surfactant, and pinonic acid (PA), a surface-active species and proxy for biogenic atmospheric oxidation products, as 2.87 × 10 and 9.38 × 10 cm molec s, respectively. In support of the experimental data, a comprehensive gas-surface-aqueous multiphase transport and reaction model of general applicability to atmospheric interfacial processes is developed. Through application of the model, PA is shown to be oxidized exclusively at the air-water interface of droplets with a diameter of 5 μm under typical ambient OH levels. In the absence of interfacial reaction, aqueous- rather than gas-phase oxidation is the major PA sink. We demonstrate the critical importance of air-water interfacial chemistry in determining the fate of surface-active species.
气相和水相是大气化学和气溶胶形成的重要介质。众多研究聚焦于水相反应以及气/水相耦合的质量传输和反应。很少有研究直接探讨在空气 - 水界面发生的过程，特别是涉及表面活性化合物的过程。我们在此报告场诱导液滴电离质谱（FIDI - MS）在大气空气 - 水界面发生的化学反应中的应用。我们测定了常见表面活性剂十二烷基硫酸钠（SDS）和气态氧化产物的表面活性替代物蒎酸（PA）在空气 - 水界面的OH自由基反应速率常数，分别为2.87×10和9.38×10 cm² molec⁻¹ s⁻¹。为支持实验数据，我们开发了一个对大气界面过程普遍适用的综合气 - 表面 - 水多相传输和反应模型。通过应用该模型，结果表明在典型的环境OH水平下，PA仅在直径为5μm的液滴的空气 - 水界面被氧化。在没有界面反应的情况下，水相而非气相氧化是PA的主要汇。我们证明了空气 - 水界面化学在决定表面活性物质归宿方面的关键重要性。
