| Particles from vehicular sources have drawn public attention for their potential to cause health risks. Beside chemical composition of these particles, their physical attributes are considered to be critical in eliciting adverse health outcomes. This thesis provides valuable information on particle physico-chemical properties with special focus on physical parameters such as size distribution, volatility, effective density, fractal dimension, surface area etc. Particle effective density and fractal dimensions were measured near a gasoline and a mixed freeway with significant diesel fleet. Diesel vehicles emit higher fraction of low density chain agglomerates compared to gasoline vehicles. Particle density at a receptor site showed interesting diurnal trend with peaks during sunny afternoons. Overall, particles demonstrated an inverse relation between size and density. Particle volatility, an important parameter to infer exposure to commuters, was measured near a pure gasoline and diesel dominated mixed-traffic freeway. Diesel particulates were associated with higher content of non-volatiles than those generated from gasoline engines and correlated excellently with the refractory elemental carbon emissions. Particle mixing characteristics not only depend on the fleet composition but also on environmental factors. Thus, to investigate the effect of meteorological conditions on particle characteristics experimental campaigns were designed to capture seasonal and diurnal variability. Although the daytime seasonal influences on particle volatility were minimal, strong diurnal changes were observed during winter. Finally, the physical characteristics of particles from diesel vehicles retrofitted with advanced emission control technologies were determined by controlled studies with a dynamomter set-up. These after treatment devices were efficient in removing solid particles, but were less effective in controlling volatile species which formed fresh nucleation mode particles. Particle volatility, density, surface diameter and extent of agglomeration were determined and compared with respect to a baseline vehicle. Our results indicate that vehicles with strong nucleation mode particles are associated with higher volatility and density and lower agglomeration. |
