Study of In-Vehicle Pollutant Variation in Public Transport Buses Operating on Alternative Fuels in the City of Toledo, Ohio

Abstract

This study focuses on determining the variation of indoor pollutants in public transport buses in the City of Toledo running on biodiesel (BD) and ultra low sulfur diesel (ULSD). The indoor pollutants monitored are carbon dioxide (CO 2), carbon monoxide (CO), sulfur dioxide (SO 2), nitric oxide (NO), and particulate matter (PM). Temperature (Temp.) and relative humidity (RH) are also measured inside the vehicle in addition to the monitored in-vehicle pollutants. The various factors generally affecting indoor air quality in any microenvironment are indoor sources of pollutants (people, furniture, etc.), ventilation, outdoor air quality, meteorology, pollutant decay, and vehicular traffic. The objective of this research paper is to study the daily, monthly, and seasonal variation of in-vehicle pollutants in relation to different variables and also determine the statistical significance of in-vehicle pollutant levels in biodiesel and ultra low sulfur diesel buses. The daily, monthly, and seasonal variations of the pollutants monitored are studied and it was observed that the pollutant level buildup within a bus compartment is due to a combination of different factors and not a result of variation due to a single variable. CO 2 levels are influenced by a combination of varying passenger ridership, vehicular traffic, ventilation settings, and bus status. CO and SO 2 levels depend on vehicular traffic, ventilation settings, and to an extent on vehicle speed. NO levels varied with vehicular traffic and ventilation settings. PM levels are influenced by vehicular traffic, ventilation settings and vehicle speed. Relatively higher pollutant concentrations are observed for the majority of pollutants in winter months when there is not much air exchange in the bus compartment. A study of the trends revealed that the concentrations were mainly influenced by peak hours, ventilation settings, vehicular traffic, passenger ridership, and meteorology. The pollutant levels of CO 2 and SO 2 are found to be statistically significantly higher in an ultra low sulfur diesel bus while the pollutant levels of CO, NO, and particle numbers with size range between 0.30 m and 0.40 m are found to be statistically significantly higher in a biodiesel bus. Particulate matter concentrations are found to be statistically similar in both the test buses.