| Organic species found in aerosols have been the focus of much activity in the atmospheric community because of their roles in human health, climate forcing, and atmospheric chemistry.{09}While chemical constituents of aerosol particles have been studied by conventional off-line techniques including GC-MS and FTIR, these methods are subject to sample discrimination based on volatility and chemical reactivity. As a result, a new crop of instruments called aerosol mass spectrometers, most of them capable of analyzing the content of a single particle, have been developed in the past fifteen years to sample aerosol particles on-line in real time. While many were successfully implemented for the study of inorganics, their application toward the field of organics has only recently been pursued by a number of groups.; In this project, a portable aerosol mass spectrometer was developed with the specific aim of studying organic species in aerosol particles. The instrument provides both size and chemical information regarding single particles. By laser velocimetry, we determine the aerodynamic size of aerosol particles. We further deduce chemical content by a two-step vaporization/laser photoionization process followed by time-of-flight mass spectrometry. Such work entailed the design and assembly of light scattering optics, timing electronics, and the mass analyzer itself.; In addition to instrumentation development, this dissertation analyzes time-of-flight peak broadening using SIMION ion optics modeling. Ion packet modeling was performed with special consideration of such issues as ion spatial distributions, initial kinetic energy, and coulombic repulsions. Modeling was shown to be a good predictor of true peak broadening.; Finally, studies performed with the laboratory-based as well as the portable instrument are detailed in chapter 4. The promise of quantitative detection in smog chamber studies of aerosols was shown for the detection of nitrogenous organic species. Soot particles were also analyzed in laboratory experiments using the portable instrument. |
