Carbon speciation of exhaust particulate matter of public transit buses running on alternative fuels

This paper examines the change from ultra-low sulfur diesel (ULSD) to biodiesel (BD) in different idling mode with respect to organic carbon (OC) and elemental carbon (EC) for public transit buses in Toledo, Ohio. The carbon source profile for both alternative fuels for eight carbon fractions was developed through real time experiments. The average OC and EC concentrations in biodiesel fueled bus were 109.53 and 12.06 μg/m3. The average OC and EC concentrations in ULSD fueled bus were 91.78 and 19.54 μg/m3. By comparison, it is clear that the ULSD fueled bus emits more elemental carbon and less organic carbon than the BD fueled bus. The OC/EC ratio was 9.82 for the BD fueled bus and 5.66 for the ULSD fueled bus. The carbonaceous fraction (CF) was 0.87 for the BD fueled bus and 0.88 for the ULSD fueled bus. The CF was 0.90 for hot idling and 0.86 for cold idling. OC1, OC2, and EC2 accounted for about 24.8%, 32.5%, and 47.2% of the Total Carbon (TC), respectively. Correlation analysis was also carried out for identifying the main fractions of OC and EC. The results indicated that the use of BD instead of ULSD is environmentally sustainable based on the above chemistry approach.