ELSEVIER Sensorsand Actuators B 38-39 (1997) 344-348 -EL CHEMICAL On-line and in situ detection of lead in ultrafine aerosols by laser-excited atomic fluorescence spectroscopy R.E. Neuhauser a, U. Panne ap*, R. Niessner a, G. Petrucci b, P. Cavalli b, N. Omenetto b a Institute of Hydrochemistry, Technical University Munich, MarchioninistraJ3e I7, D-81377 Manich, Germany b European Commission, Joint Research Center Ispra, Environment Institute, I-21020 Ispra (Varese), Italy Abstract 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(NOs)a 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 mm3 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. Keywords: Ultrafine aerosols; Differential mobility particle sizer (DMPS); Lead; Laser-induced plasma; Laser-excited atomicfluorescence (LEAF) 1. Introduction Atmospheric aerosols are a complex mixture of particles derived from diverse anthropogenic and biogenic sources. The urge to understand global climate change has led to an increased interest in aerosols, which are consideredimportant for the chemistry of both the stratosphere and troposphere (see e.g., [l-4] and refs. therein). Most of the current research on environmentally relevant aerosols is focused on ultrafine particles, i.e., particles with diameters < 1 pm. On- line analysis of particle size and composition can provide vital clues concerning the origin, formation, transport, reac- tivity, transformation, reactions and environmental impact of aerosols [5]. Most atmospheric processes for ultrafine par- ticles are of the order of seconds or minutes, so that asufficient time resolution is necessary for on-line measurement of these aerosols [ 61. Similar analytical needs for particle analysis are found in industrial hygiene, e.g., particles at workplaces. Particles with diameters below 1 pm are frequently enriched with toxic species and can penetrate deep into the respiratory tract when inhaled. Consequently, the biological effects of * Corresponding author. Phone: +49 89 7095 7980. Fax: f49 89 7095 7999. 0925-4005/97/$17.00 0 1991 Elsevier Science S.A. All rights reserved P1~s0925-4005(96)02109-0 exposure to thoracic particle fractions may be severe and rapid, even for short periods at high concentration [7,8]. The objective of this work was to develop an analytical method based on laser-excited atomic fluorescence (LEAF) [9-l 11 with flame atomization (FA) or a laser-induced plasma (LIP) [ 12,131 as atom source, which provides on- line and size-segregated information on the elemental chem- ical composition of ultrafine aerosols. As a representative aerosol system, we have chosen ultrafine lead nitrate aerosols. Lead is enriched in aerosols of anthropogenic origin by sev- eral orders of magnitude relative to crustal sources (urban atmosphere, 20-400 ng me3; remote areas, 2-150 ng me3 [ 14,151). Hence, lead is generally accepted as an anthropo- genie marker, although the considerable reduction of Pb from leaded gasoline has given rise to a reduction of 30-50% in total lead input into the atmosphere [ 15-181. 2. Experimental set-up An ultrasonic nebulizer (U-5OOOAT+, CETAG Technol- ogies Inc., Omaha, USA) with an integrateddrier was utilized for the production of spherical ultrafine lead nitrate aerosols. Nebulization of aqueous Pb (NO,), solutions with concen- trations between 200 ppb and 10 ppm resulted inpolydisperse