Characterization of vehicular exhaust emissions and indoor air quality of public transport buses operating on alternative diesel fuels

Over the years, vehicular traffic has increased multifold causing an associated increase in the total emissions from transportation sources. These vehicular emissions affect two human occupied environments most significantly: human occupied regions near and around the roads including residences, offices, schools, hospitals etc., and indoor vehicle compartments that act as individual microenvironments trapped inside the high concentration zone. A detailed literature review indicated five major gaps in the knowledge base related to pollutant characteristics from the vehicular exhaust and pollutant behavior inside buses which are addressed in this research. (1) Characterization of indoor air pollutant behavior: The literature review did not yield any elaborate study results on indoor pollutant behavior trends and/or models for public transport bus compartments. Comparative studies on the behavior of indoor-outdoor pollutant relationships and concentration variation at different locations inside the bus were also limited in scope. (2) Indoor air quality in buses and factors influencing the indoor air quality (IAQ): No comprehensive study has been reported in the literature in which simultaneous measurement of multiple gaseous contaminants and particulate matter (PM) inside buses have been carried out that have focused on the identification of important explanatory variables of indoor air quality. (3) Measurement of fine particulates: The current work reported in the literature is limited to particulate measurements for sizes more than 2.5 micrometer (mum) and most of the studies focus on PM10 (particle matter less than 10 mum in diameter) concentrations. Very few studies have measured the number of particles/unit volume and compared the associated abundance of particles to their respective mass concentrations. (4) Characterization of exhaust emission behavior: Most of the work reported has a limitation on the number of vehicles studied and fails to elaborate the interaction between influencing variables. Very few studies have reported emission comparisons for biodiesel and ultra-low sulfur diesel (ULSD) operated fleets and limited models are available to study fleet emission behavior and instantaneous emission concentrations with respect to engine performance and fuel. (5) Impacts of alternative fuels on indoor air quality have not been studied extensively.; This research has tried to lessen these knowledge gaps in the field and is the first to attempt an extensive real time monitoring and measurement of numerous operational and traffic variables that could have an effect on the emissions and the air quality of public transport buses. A comprehensive emission testing protocol was developed for characterizing emission characteristics from Toledo Area Regional Transportation Authority (TARTA) public transport buses, and over 120 buses were tested in engine idling and on-road operation modes. This research was also the first to attempt a comprehensive indoor air quality study spanning thirteen months of data collection involving the monitoring and measurement of multiple indoor gaseous pollutants and ultra-fine particulate number and mass concentrations.; In conclusion, this dissertation demonstrates a feasible strategy for developing a comprehensive emission inventory and indoor air quality database to study the indoor and ambient impacts of public transport buses. The dissertation also presents a new analysis procedure for identifying the potential impact of each influencing variable from a comprehensive multi-variable environmental database developed from an experimental procedure. This research is also the first to attempt a comprehensive study to characterize the ultra-fine particulate (PM<1.0 mum) behavior inside public transport buses and to develop predictive models for multiple indoor pollutants including fine and ultra-fine particulate mass and number concentrations. The research was also able to characterize the emissio...