On-line and in-situ detection of polycyclic aromatic hydrocarbons (PAH) onaerosols via thermodesorption and laser-induced fluorescence spectroscopy

A fiber optical sensor system for the determination of polycyclic aromatic hydrocarbons (PAH) on aerosols by laser-induced, time-resolved fluorescence is combined with a thermodesorption device. The sensor system is based on an aerosol flow cell, which is fibre-optically coupled to a pulsed nitrogen laser for excitation and the detection system. Time-resolved fluorescence emission spectra are detected by a monochromator equipped with a photomulti plier and a fast digital storage oscilloscope. The analytical figures of me rit of the thermodenuder are reported for benzo[a]pyrene, benzo[b] fluorant hene, and benzo[ghi] -perylene on ultrafine soot and NaCl aerosols By therm odesorption of the PAH, problems due to quenching of the PAH fluorescence b y the bulk aerosol material or excimer formation on the aerosol surface wer e avoided. For the PAH under study, the sensitivity was improved considerab ly and detection limits between 110 and 850 ng m(-3) were attained, while a response time of 2-3 min was achieved with the thermodenuder. A calibratio n for PAH on ultrafine soot and NaCl aerosols was established independent o f the aerosol substrate.