Abstract
This thesis is concerned with measurements and modelling of the dispersion of nanoparticles (those below 300 nm) in street canyons and in the wake of moving vehicles. This work determines the competing influences of meteorology, traffic volume and particle dynamics (dilution and transformation) on particle number distributions (PNDs) and concentrations (PNCs) in various size ranges. Experimental studies were carried out using an advanced particle spectrometer to measure the PNDs and PNCs. Several important findings were drawn from these studies. These included the size range and distribution of particles dominating the total ambient PNCs, particle number emission factors for typical streets and driving conditions, the importance of particle dynamics during roadside measurements, and numerous sub-models relating the PNCs in various size ranges with canyon height, meteorology and traffic volume. The key findings were used to formulate a modified Box model for the dispersion of particles in street canyons. Measured PNCs were then compared and found to be within a factor of 3 of those modelled using the modified Box model, an operational model and a computational fluid dynamics model (FLUENT). These results suggested that a simplified approach can predict the PNCs to accuracy comparable with that obtained using more complex models, if model inputs are chosen carefully. Research findings from this work can assist regulatory authorities to frame limits of particles on a number basis. They may also be used to validate and refine the capabilities of existing models for the dispersion of particles and aid in their extension towards a prediction of PNDs.