Modeling The Evolution Of Vehicle Exhaust Plume Near Road And In Laboratory Dilution Systems Using The Ctag Model
There are a growing number of people living or spending substantial time near major roadways, being exposed to elevated traffic-related pollutants. Due to their adverse health effect, it is imperative to reduce the uncertainties in the traffic emission inventory and characterize the spatial and temporal impacts of pollutants on near-road air quality, which is critical to assessing human exposure. This dissertation presents the development and applications of an environmental turbulent reacting flow model, the Comprehensive Turbulent Aerosol Dynamics and Gas Chemistry (CTAG) model. CTAG is designed to simulate the transport and transformation of multiple air pollutants in various environments. For near-road applications, CTAG couples the major turbulent mixing processes with gas-phase chemistry and aerosol dynamics. CTAG demonstrates that significant improvement in predicting the spatial gradients of pollutants near roadways can be achieved by detailed treatment of turbulence characteristics. It is commonly assumed that the NO2/NOx ratio by volume for most roadways is 5%. However, this dissertation is the first to show that this assumption may not be suitable for most roadways, especially those with a high fraction of heavy-duty truck traffic. It also illustrates that the dynamics of exhaust plumes are highly sensitive to vehicle-induced turbulence, sulfuric acid induced nucleation, and condensation of organic compounds. It simulates, for the first time, the multi-scale aerosol dynamics and microenvironmental air quality by introducing a multi-scale structure to generate the processed on-road particle emissions. It implies that roadway and surrounding infrastructure designs can affect near-road air quality. CTAG can be used to improve the regulatory model in assessing the air quality in near-road environments. The turbulent reacting flows inside the fabricated dilution systems are also investigated since they are essential to most emission testing procedures and share the same mechanisms with the atmospheric dilution. CTAG investigates the effects of the dilution parameters and illustrates that turbulence plays a crucial role in mixing the exhaust with the dilution air, and the strength of nucleation dominates the level of particle emissions. A potential unifying parameter, the dilution rate of exhaust, is found to play an important role in new particle formation. Using the CTAG model, urban planners have the potential to develop strategies to reduce the uncertainties associated with dilution samplings and define a standardized dilution sampling methodology for characterizing emissions from multiple combustion sources.
Pope, Stephen Bailey; Koch, Donald L
Ph.D. of Mechanical Engineering
Doctor of Philosophy
dissertation or thesis