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Published August 9, 2018 | public
Journal Article Open

Probing the OH Oxidation of Pinonic Acid at the Air-Water Interface Using Field-Induced Droplet Ionization Mass Spectrometry (FIDI-MS)


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^(–8) and 9.38 × 10^(–8) cm^2 molec^(–1) s^(–1), 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.

Additional Information

© 2018 American Chemical Society. Received: June 4, 2018; Revised: July 16, 2018; Published: July 16, 2018. This work was supported, in part, by National Science Foundation grant AGS-1523500. R.Z. acknowledges support from Natural Science and Engineering Research Council of Canada Postdoctoral Fellowship (NSERC-PDF). C.W. acknowledges helpful discussion on COSMOtherm surface partitioning predictions with Dr. Jens Reinisch and Dr. Frank Eckert from COSMOlogic. Author Contributions: Y.H., K.M.B.: These authors contributed equally to this work. The authors declare no competing financial interest.

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August 19, 2023
August 19, 2023