Measurements of Lead Vapor and Particulate in Flames and

this paper we use excimer laser fragmentation -fluorescence (ELFFS) spectroscopy for detecting toxic metal species. In ELFFS, an excimer laser is used to photofragment molecules. Excess energy from photofragmentation can excite electronic states of fragment atoms and molecules, which are detected using fluores- cence. A 193 nm ArF excimer laser is close enough to the vacuum UV that most molecules have a significant absorbance of the laser light [26]; using the single-laser ELFFS technique we detect six out of twelve toxic metals tested in post-flame gases, including Pb [27]. Other researchers have used this technique to measure concentrations of alkali metals in coal combustors [28 --30]. The relevant energy levels of Pb are shown in Fig. 1. When single-laser ELFFS is conducted in post-flame gases containing Pb, all 436 S. G. BUCKLEY ET AL. of the emission lines in Fig. 1 are observed. Single-laser ELFFS excites fluorescence from molecules and from particles containing metals. A variant of ELFFS is the two-laser ELFFS technique, which we have used previously to measure chlorinated hydrocarbons [31, 32]. Here a second laser probes the fragment molecules to excite fluorescence. In the case of Pb, we excite ground state atomic fluorescence; hence this measurement yields emission from both nascent Pb(g), and Pb(g) produced from photofragmentation of either aerosol or molecular species. Two-laser ELFFS allows probing of the decay of Pb(g) following photofragmentation, which may be as a result of reaction or condensation. The same emission lines are observed as in the LIF measurement