Reactive uptake of ozone by chlorophyll at aqueous surfaces

We report the results of two complementary studies of the heterogeneous reaction between gas-phase ozone and aqueous chlorophyll. In the first experiment, the chlorophyll is present at the air-water interface and its concentration is measured as a function of time, using laser-induced fluorescence, to obtain the surface kinetics. Under most experimental conditions, these are well described using a Langmuir-Hinshelwood formalism. The second experiment was carried out in a wetted-wall flowtube apparatus and measured the uptake coefficient of ozone by the chlorophyll solution. The uptake coefficient decreases with increasing ozone concentration, consistent with the surface mechanism found in the fluorescence experiment. The two experiments agree that the uptake coefficient for ozone by such chlorophyll samples is approximately 2-5 x 10(-6) with unpolluted boundary layer ozone concentrations. At low wind speed, the reaction between ozone and chlorophyll at the sea surface may represent the driving force for ozone deposition at the ocean surface, significantly increasing its deposition velocity there.