1 research outputs found
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<sup>–8</sup> and 9.38 × 10<sup>–8</sup> cm<sup>2</sup> molec<sup>–1</sup> s<sup>–1</sup>,
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