On-line and in-situ detection of lead aerosols by plasma-spectroscopy and laser-excited atomic fluorescence spectroscopy

A set-up for on-line and size-segregated detection of lead in ultrafine aerosols was developed. Lead nitrate aerosols with particle diameters between 10 and 300 nm were generated by ultrasonic nebulization of aqueous Pb(NO₃)₂-solutions. A differential mobility particle sizer (DMPS) was used for size-resolved mass calibration. Either a miniaturized acetylene-air- flame or a laser-induced plasma (LIP) was employed for atomization. Lead was detected with a spectrograph and a gateable, intensified CCD-camera by atomic emission spectroscopy (AES) and laser excited atomic fluorescence (LEAF). Due to the lower sensitivity, for LIP-AES no size-resolved calibration was possible and for calibration with polydisperse aerosols a detection limit of 155 μg m^-3 was found for lead. With LEAF and flame atomization, a linear calibration curve was obtained with on-line detection limits of 47 ng m^-3 for lead. No dependence of the detection limit on the particle diameter was observed. For LEAF with a laser-induced plasma as atom source, a correlation between the detection limit and the particle diameter was found. The detection limit increased from 55 ng m^-3 for a particle diameter of 48 nm to 130 ng m^-3 for a particle diameter of 300 nm. The increasing detection limit with increasing particle diameter was probably due to the incomplete atomization of larger particles in the colder periphery of the plasma.