UBC Undergraduate Research

A School Bus Air Quality Evaluation and A Feasibility Analysis of Converting to Electric from Diesel Buses Fu, Sylvester; Ng, Steuart Malvin Tannason; Chen, Wenhao


Background This report is compiled as part of the ENVR 400 community project deliverable to both the Environmental Sciences Department of the University of British Columbia and the Sunshine Coast Clean Air Society (SCCAS). Among miscellaneous atmospheric pollutants, PM ₂.₅ officially refers to fine particles with a diameter less than 2.5 μm, which can pose significant threats to the respiratory health of people, especially vulnerable groups like schoolchildren. The project, proposed by SCCAS, seeks to answer two questions: 1. When commuting on school buses, are schoolchildren exposed to higher levels of PM₂.₅ compared to the ambient level, and the provincial and national standards? 2. How feasible would switching from diesel to electric buses be, based on the costs and benefits between purchasing an electric bus and a diesel bus? Method Brief The DC1700 air quality monitoring instrument was used to determine schoolchildren’s exposure to PM₂.₅ on board different school buses and at different school stops across Sunshine Coast during the afternoon commutes. PM₂.₅ concentrations are plotted on time series plots based on data logs during the data collection stage in attempt to discover possible correlations between miscellaneous events and significant changes in concentrations. The one-hour average from each sampling trip was compared against the provincial and national air quality standards as a means of determining whether children are exposed to higher or lower levels of particulate matter. An analysis of variance (ANOVA) was also conducted to explore the statistical significance of the difference in concentrations on and off school buses. As for conducting an appraisal of the feasibility of purchasing an electric bus instead of a diesel bus, a cost-benefit analysis (CBA) using a discounted cash flow method was employed. The values used in the analysis are derived from different sources ranging from scholarly literature, online sources, and the information provided by Thirdwave Bus Company. Three-standard investment decision-making criteria – the present value of aggregate net benefits (ANB), internal rate of return, and discounted payback period – were used to determine whether purchasing an electric bus would be more beneficial relative purchasing to a diesel bus. Principal Findings Both the one-hour average on-board and bus-stop PM₂.₅ concentrations were found to be lower than provincial and national standards, but there were times during the sampling period when the standards were exceeded. Overall, there was no clear relationship between logged events – primarily doors opening and closing – and spikes and troughs in our time series plots, which are potentially attributable to factors such as influences from meteorology, number of occupants, and external sources of pollutants. The ANOVA also showed that the PM₂.₅ concentrations on board the school buses were significantly higher than those at bus stops. The CBA demonstrates positive annual monetary benefits in all years except in year 0 and year 9, when the bus purchase and battery replacement occur, respectively. Overall, purchasing an electric bus instead of a diesel bus yields more benefits since the internal rate of return is above the discount rate, the discounted payback period is below the average lifespan of a bus, and both the public and private ANB are positive. However, based on the sensitivity analysis, this feasibility is highly contingent on the presence of a V2G (vehicle-to-grid) system and low capital cost of electric buses - the two parameters that the ANB was most sensitive to.

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