| In response to the need for discrete characterization of ambient air fine particles due to the direct relation of particle size and particle composition to human health effects, laser-induced breakdown spectroscopy (LIBS) has been studied in this dissertation to support its development as a real-time aerosol analysis technique capable of measuring particle size and particle composition.; In Chapter 1, a literature review and the principles of LIBS are presented in the context of aerosol analysis. The complete experimental facilities are described in Chapter 2. An aerosol generation system was developed to produce well-dispersed aerosolized nanoparticles that served as the calibration source for the LIBS system. The LIBS system consists of a 1064-nm Nd:YAG pulse laser, supporting optics, and an intensified charge-coupled device for plasma emission quantification. The developed LIBS system was successfully deployed as discussed in Chapter 3 for ambient air monitoring (specifically aluminum, magnesium, calcium, and sodium). Mass concentrations were recorded on the order of low parts per trillion and minimum particle sizes about 200 nm. In Chapter 4, issues of plasma homogeneity and signal fluctuations on a shot-to-shot basis were addressed to elucidate optimal laser pulse energy for single shot analysis, thereby identifying a characteristic state of the plasma where signal fluctuations are minimized. The implicit assumption of complete particle vaporization is investigated in detail in Chapter 5, with the determination that silica particles up to 2.1-μm diameters are completely vaporized due to plasma-particle interactions. Finally, the characteristic plasma volumes related to the scheme of particle sizing are determined and analyzed in the context of the analysis of single aerosol particle detection.; The outcome of this research yielded an enhanced understanding of single aerosol analysis with the LIBS technique. Important conclusions are that LIBS measurement should be made at the plasma saturation condition, particle sizing should be limited to about 2 μm or less, particle vaporization is driven by plasma-particle interactions, and that real-time ambient air monitoring is feasible with LIBS on time periods as short as 4 minutes. |
