Many atmospherically important chemical processes are believed to occur at the interface between the air
and aqueous phases. We report the first direct measurement of the kinetics of a reaction between a gas-phase
species (ozone) and a compound (anthracene) adsorbed at the air−water interface. The reaction was studied
at the “clean” air−water interface and also at an interface consisting of approximately one monolayer of
1-octanol. In both instances, the reaction was seen to follow a Langmuir−Hinshelwood mechanism, in which
ozone first adsorbs to the surface and then reacts with adsorbed anthracene. Using typical atmospheric ozone
concentrations, a reactive uptake coefficient of approximately 6 × 10-8 at the air−water interface may be
estimated; this value increases by about a factor of 5 when the water surface is coated by a monolayer of
1-octanol.
We report direct laser-induced fluorescence measurements of the uptake of the polycyclic aromatic hydrocarbons
(PAHs) anthracene and pyrene to the air−aqueous interface for pure water and for water coated with an
organic film. The surface uptake coefficients of anthracene and pyrene to the air−water interface are estimated
to be on the order of 10-5. For both PAHs, the surface uptake coefficients for uptake to a 1-octanol-coated
water surface increase by a factor of 2−3 over those determined for the pure water surface. The surface
uptake of pyrene to a hexanoic-acid-coated interface does not display this enhancement, though there is a
small enhancement of its equilibrium partitioning to hexanoic-acid-coated surfaces. Resolved fluorescence
spectra of pyrene adsorbed onto 1-octanol-coated surfaces indicate that pyrene is in a less polar environment
there than when adsorbed at hexanoic-acid-coated interfaces.
Abstract.A quartz crystal microbalance apparatus has been used to measure the room temperature uptake of water vapour by thin films of oleic acid as a function of relative humidity, both before and following exposure of the films to various partial pressures of gas phase ozone. A rapid increase in the water-sorbing ability of the film is observed as its exposure to ozone is increased, followed by a plateau region in which additional water is taken up more gradually. In this fully-processed region the mass of water taken up by the film is about 4 times that of the unprocessed film. Infrared spectra of the films, measured after variable exposures to ozone, show dramatic increases in both the "free" and hydrogenbonded O-H stretching regions, and a decrease in the intensity of olefinic features. These results are consistent with the formation of an oxygenated polymeric product or products, as well as the gas phase products previously identified.
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