Measuring In-Cabin School Bus Tailpipe and Crankcase PM^sub 2.5^: A New Dual Tracer Method

• Published in: Journal of the Air & Waste Management Association (1995) Vol. 61; no. 5; p. 494
• Main Authors: Ireson, Robert G, Ondov, John M, Zielinska, Barbara, Weaver, Christopher S, Easter, Michael D, Lawson, Douglas R, Hesterberg, Thomas W, Davey, Mark E, Liu, L-J Sally
• Format: Journal Article
• Language: English
• Published: Pittsburgh Taylor & Francis Ltd 01.05.2011
• Subjects: Emissions; Experiments; Health sciences; Lubricating oils; Methods; Studies; Vehicles
• ISSN: 1096-2247; 2162-2906

Exposures of occupants in school buses to on-road vehicle emissions, including emissions from the bus itself, can be substantially greater than those in outdoor settings. A dual tracer method was developed and applied to two school buses in Seattle in 2005 to quantify in-cabin fine particulate matter (PM^sub 2.5^) concentrations attributable to the buses' diesel engine tailpipe (DPM^sub tp^) and crankcase vent (PM^sub ck^) emissions. The new method avoids the problem of differentiating bus emissions from chemically identical emissions of other vehicles by using a fuel-based organometallic iridium tracer for engine exhaust and by adding deuterated hexatriacontane to engine oil. Source testing results showed consistent PM:tracer ratios for the primary tracer for each type of emissions. Comparisons of the PM:tracer ratios indicated that there was a small amount of unburned lubricating oil emitted from the tailpipe; however, virtually no diesel fuel combustion products were found in the crankcase emissions. For the limited testing conducted here, although PM^sub ck^ emission rates (averages of 0.028 and 0.099 g/km for the two buses) were lower than those from the tailpipe (0.18 and 0.14 g/km), in-cabin PM^sub ck^ concentrations averaging 6.8 µg/m^sup 3^ were higher than DPM^sub tp^ (0.91 µg/m^sup 3^ average). In-cabin DPM^sub tp^ and PM^sub ck^ concentrations were significantly higher with bus windows closed (1.4 and 12 µg/m^sup 3^, respectively) as compared with open (0.44 and 1.3 µg/m^sup 3^, respectively). For comparison, average closed- and open-window in-cabin total PM^sub 2.5^ concentrations were 26 and 12 µg/m^sup 3^, respectively. Despite the relatively short in-cabin sampling times, very high sensitivities were achieved, with detection limits of 0.002 µg/m^sup 3^ for DPM^sub tp^ and 0.05 µg/m^sup 3^ for PM^sub ck^. [PUBLICATION ABSTRACT]