Using continuous air monitoring devices, we investigated sources and solutions to cabinparticulate matter pollution in conventional diesel school buses in five U.S. Cities. Air qualitymonitoring, designed to document self-pollution, was conducted inside conventional schoolbuses before and after installation of retrofit emissions controls. Buses were tested during idlingand on residential bus routes. Residential routes afforded the ability to document bus-selfpollution due to few or no external sources of diesel exhaust in the residential areas to confoundresults. A lead car equipped with identical instrumentation traveled ahead of the bus as a control.We documented diesel particulate matter exhaust routinely penetrating the bus cabin from thetailpipe and the engine compartment through the open front door at bus stops. Elevated in-cabinconcentrations of ultrafine particles, black carbon and particle-bound PAH (PPAH) during busroutes, idling, and queuing, were associated with emissions from the bus tailpipe. In contrast,fine mass (PM2.5) was dominated by particulate matter emissions documented from the enginecrankcase. Crankcase emissions proved to be an extremely strong source of PM2.5in the schoolbus, dominating cabin PM2.5 self-pollution.Buses were retrofit with combinations of both tailpipe and crankcase emissions control devices,including catalyzed diesel particulate filters (DPFs, e.g. The Johnson Matthey CRT?), crankcasefiltration devices (e.g. The open crankcase Fleetguard Enviroguard and the closed crankcaseDonaldson Spiracle?), diesel oxidation catalysts (DOCs), ultralow sulfur diesel fuel, and B100biodiesel fuel. (Note that these tests were done prior to the nationwide ULSD mandate and thus,conventional fuel is the baseline fuel in this study unless otherwise noted.)The DPF-closed crankcase combination resulted in elimination of cabin particulate matter selfpollutionfor all measured parameters including ultrafine particles (particle number), blackcarbon, PPAH and PM2.5. The Spiracle?, a closed crankcase ventilation filter (commonlyabbreviated “CCV”)—by itself-- reduced PM2.5 mass to near ambient from the cabins of all buseswith the installed device. These results are robust and were largely repeated in the 5 cities.Importantly, the results of the DOC retrofit and B100 fuel runs stand in stark contrast to theDPF-CCV reductions, suggesting that these combinations have, at best, limited usefulness as adevice to remedy in-cabin ultrafine particulate matter air quality. Instead, we find that the CCVwas comparable in cost to the DOC (under $1,000 including installation) but much moreeffectively eliminated in-cabin PM2.5. While EPA has verified CCVs in combination with DOCs,results of this study suggest that EPA should consider separate stand-alone closed-crankcase
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