Kinetics and products of the reaction of gas-phase ozone with anthracene adsorbed at the air–aqueous interface

Many atmospherically important chemical processes occur at the interface between the air and aqueous phases, such as the surfaces of oceans, lakes and atmospheric aerosols. We have measured the kinetics and the products of a reaction between gas-phase ozone and anthracene adsorbed at the air–aqueous interface. The intensity of the laser-induced fluorescence from adsorbed anthracene is used to follow the reaction kinetics; GC-MS identifies 9,10-anthraquinone as the major product. Reactions at the “clean” air–water interface and at an interface consisting of a monolayer of various amphiphilic organic compounds were studied. In all cases, the reaction follows a Langmuir–Hinshelwood mechanism, in which ozone first adsorbs to the air–aqueous interface, then reacts with already adsorbed anthracene. For typical atmospheric ozone concentrations, the estimated gas-surface reaction probability ranges from 2×10−8 to 3×10−7 depending on the nature of the air–aqueous interface. Small carboxylic acids at the interface are found to inhibit the reaction (compared to the “clean” water surface); 1-octanol enhances it. Under some circumstances, oxidation of anthracene by ozone on aqueous surfaces may be of comparable importance in the atmosphere to gas phase oxidation by OH.