Laser induced fluorescence of pyrene at an organic coated air-water interface

A laser induced fluorescence method has been developed to study adsorption of polycyclic aromatic hydrocarbons ( PAHs) at an air water interface coated with an organic film. This method allows a direct probe of the mechanisms and extent of PAH uptake by the organic coated-water surface. In this study, we present results of pyrene partitioning to the hexanoic acid coated water surface. The fluorescence emission spectra and lifetimes of pyrene measured at the pure water air interface, pure hexanoic acid air interface, and water surfaces coated with a sub-monolayer or multi-layer of hexanoic acid suggest partitioning of pyrene to the air solution interface. There is an enhanced adsorption of pyrene at the hexanoic acid-coated water surface, even with sub-monolayer coverages of hexanoic acid. The surface concentration of pyrene increases linearly with its bulk concentration until a saturation point, which is dependent on the amount of hexanoic acid present at the surface. Implications for reactivity of PAHs at organic coated atmospheric water droplets and aerosols are discussed.