Measuring In-Cabin School Bus Tailpipe and Crankcase PM2.5: A New Dual Tracer Method

• Published in: Journal of the Air & Waste Management Association (1995) 2011-05, Vol.61 (5), p.494-503
• 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: Article
• Language: English
• Subjects: Applied sciences; Atmospheric pollution; Automobiles; Automotive engineering; Buses; Buses (vehicles); carbonaceous emissions; Combustion products; Detection limits; Deuteration; Diesel; Diesel engines; Emission analysis; Emission measurements; Emissions; Emissions control; ENVIRONMENTAL SCIENCES; Exact sciences and technology; Exhaust emissions; Exposure; Fuel combustion; Iridium; Lubrication; Oil pollution; organometallic iridium tracer; Particulate emissions; Particulate matter; Pollution; Pollution sources; School buses; Vehicle emissions; Ventilation
• ISSN: 1096-2247; 2162-2906
• DOI: 10.3155/1047-3289.61.5.494

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 2.5 ) concentrations attributable to the buses' diesel engine tailpipe (DPM tp ) and crankcase vent (PM 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 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 ck concentrations averaging 6.8 μg/m 3 were higher than DPM tp (0.91 μg/m 3 average). In-cabin DPM tp and PM ck concentrations were significantly higher with bus windows closed (1.4 and 12 μg/m 3 , respectively) as compared with open (0.44 and 1.3 μg/m 3 , respectively). For comparison, average closed- and open-window in-cabin total PM 2.5 concentrations were 26 and 12 μg/m 3 , respectively. Despite the relatively short in-cabin sampling times, very high sensitivities were achieved, with detection limits of 0.002 μg/m 3 for DPM tp and 0.05 μg/m 3 for PM ck .