Application of time-resolved fluorescence spectroscopy on the analysis of pah-coated aerosols

A fiberoptic sensor system was developed for the detection of PAH-coated aerosols. It incorporates a pulsed nitrogen laser for excitation and a monochromator, a photomultiplier and a digital storage oscilloscope for recording of fluorescence decay curves. With a software-realized photon counting technique detection limits less than 100 ng/m³ for most of the PAHs investigated were achieved with NaCl as a substrate (e.g., 20 ng/m³ for benzo(e)pyrene on NaCl). The sensitivity of the system decreased dramatically when PAH adsorbed on carbon aerosol were analyzed. With pyrene on polydisperse NaCl aerosol the formation of excimers was observed and the formation kinetic could be analyzed. With benzo(e)pyrene on NaCl under similar conditions excimer fluorescence was observed but not the formation kinetic. This indicates the formation of micro-crystals of PAHs on aerosol surfaces even at surface coverages Θ ≪1. Due to the observed matrix effects experiments were carried out, at which the PAHs were thermally desorbed in advance of the analysis. By this PAH fluorescence was measurable with carbon as matrix.