| Recent epidemiological studies have demonstrated a correlation between adverse health effects and exposure to diesel particulate matter (DPM). Subsequent studies have been conducted in attempts to identify the source and/or causal mechanisms for the observed health effects. In order to shed light on the correlation between DPM and health effects, this dissertation reviews highlights of previous work and investigates a hypothesis that considers metal-bearing DPM as a possible contributor. Literature is cited which supports a hypothesis that by-product metals are produced during diesel combustion and reside on ultrafine particles that can easily be deposited in the lungs by inhalation. To investigate that hypothesis, research experiments were designed and conducted utilizing a diesel engine to generate particles. Emitted particles were analyzed using techniques including electron microscopy, x-ray diffraction, and single particle mass spectrometry.; Analysis was aimed at providing a better understanding of the role of metals during diesel combustion. Three sets of experiments were designed to quantify the fate of various metals during the combustion process. The first two experiments represent cases where the metals were relatively easily quantifiable, since the fuel was doped with iron (20--60ppm) or with lube oil containing metallic additives. The third experiment describes the least quantifiable case, i.e. where there was no doping. The latter case addresses real world conditions and in that sense is the most critical. However, the other experiments provided insight into the dynamics of particle formation and in that regard stand on their own. Research results illustrate that for both doped and undoped conditions, trace metals are associated with particles in the size range of about 20--300 nm mobility diameter. For some cases the metal to carbon ratios for these particles are inversely proportional to particle diameter, suggesting condensation of metal vapors onto carbon particles. Results also show that for the doped cases, the slightly higher metal content in the system leads to formation of metal-rich nanoparticles. |
