Real-time analysis of individual aerosol particles by laser ablation (Maryland).

摘要

The research presented in this dissertation focuses on the characterization of ambient, urban aerosol particles by real-time laser ablation analysis. The bulk of this research was performed with a single particle mass spectrometer (SPMS) that incorporated aerodynamic particle sizing, laser ablation, and dual-polarity, time-of-flight mass spectrometry. From March--December, 2002, the SPMS analyzed over 381,000 particles in Baltimore, MD. While nitrate, sulfate, and carbon (elemental or organic) were found to dominate the Baltimore aerosol, over 10% of the detected particles contained transition and/or heavy metals.; Size distributions, number concentrations, time/wind dependencies and intraparticle correlations between metals were determined for the metal containing portion of the Baltimore aerosol. During cooler months, vanadium was found to be multidirectional in origin. Iron and lead were observed from the east-northeast and were present in the same particles suggesting a common source. Arsenic and lead were observed from the south-southeast. Particles from this direction contained either arsenic or lead but rarely both, suggesting different sources for each element.; Two-types of ultrafine nitrate particle creation events were observed in Baltimore. The first type was a large burst of nominally "pure" nitrate particles in the 50--90 nm size range, and a smaller burst of "pure" particles in the 50--90 nm size range that grew to 110--220 nm with time. Coincident with both of these events was an increase in the number of mixed composition particles containing nitrate, suggesting that they were formed by condensation of ammonium nitrate onto pre-existing particles.; The particle composition types most commonly associated with sulfate were determined for the Baltimore aerosol. Particle types strongly correlated with sulfate are nitrate, organic carbon - ammonium nitrate and vanadium. Particle types weakly associated with sulfate include carbon and potassium/sodium. Results suggest that sulfate detection by this method is a reasonable indicator of particle source and atmospheric transformation.; A novel, portable instrument that incorporates ion mobility spectrometry (IMS), laser induced breakdown spectroscopy (LIBS), and aerodynamic particle sizing was developed for single particle analysis. IMS was found to work best for characterizing organic components while LIBS was found to be well suited for inorganic components, particularly metals.