Direct Observation of the Kinetics of an Atmospherically Important Reaction at the Air−Aqueous Interface

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.