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

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