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Abstract: We monitored two Seattle school buses to quantify the buses’ self pollution using the dual tracers (DT), lead vehicle (LV), and chemical mass balance (CMB) methods. Each bus drove along a residential route simulating stops, with windows closed or open. Particulate matter (PM) and its constituents were monitored in the bus and from a LV. We collected source samples from the tailpipe and crankcase emissions using an on-board dilution tunnel. Concentrations of PM1, ultrafine particle counts, elemental and organic carbon (EC/OC) were higher on the bus than the LV. The DT method estimated that the tailpipe and the crankcase emissions contributed 1.1 and 6.8 μg m−3 of PM2.5 inside the bus, respectively, with significantly higher crankcase self pollution (SP) when windows were closed. Approximately two-thirds of in-cabin PM2.5 originated from background sources. Using the LV approach, SP estimates from the EC and the active personal DataRAM (pDR) measurements correlated well with the DT estimates for tailpipe and crankcase emissions, respectively, although both measurements need further calibration for accurate quantification. CMB results overestimated SP from the DT method but confirmed crankcase emissions as the major SP source. We confirmed buses’ SP using three independent methods and quantified crankcase emissions as the dominant contributor. [Copyright &y& Elsevier]

In China particulate matter (PM) is the leading environmental risk factor to morbidity and mortality, with transport being the main source of PM pollution in cities. China VI emission limit standards, which are one of the most stringent worldwide, have only recently been introduced and there is lack of studies assessing the PM emissions of new engines. In Europe, there are discussions ongoing to permit sampling directly from the tailpipe with fixed dilution for determining the solid particle number (SPN) emissions during type approval of heavy duty engines; something that is practically allowed for on-road testing. In this study the particulate emissions of seven engines were measured. Three of them were fulfilling the China VI limits, two China V, while two of them were China III engines retrofitted with diesel particulate filters (DPFs). One system with evaporation tube was installed at the full dilution tunnel, as prescribed in the regulation, and another one with catalytic stripper was sampling from the tailpipe, both measuring >23 nm and >10 nm particles. The results showed a wide range of particulate emission levels depending on the engine, the existence of a DPF, the connection point of the crankcase ventilation, and the occurrence of active or passive regeneration. The system at the tailpipe measured on average 20% lower than the system at the dilution tunnel. The system at the dilution tunnel measured much higher during one regeneration due to re-nucleation of volatiles downstream of the evaporation tube. For one engine, the emissions of the evaporation tube system were more than double when the crankcase ventilation was connected downstream of the aftertreatment devices. The main message from this study is that a catalytic stripper is necessary for sub-23 nm measurements and tailpipe sampling with fixed dilution is a plausible option. • China III to VI engine particulate matter (PM) mass and particle number (PN) emissions. • Filtration efficiency of retrofitted diesel particulate filters. • Comparison of PN systems measuring from the tailpipe and the full dilution tunnel. • Contribution of crankcase ventilation to engine emissions. • Passive and active regeneration emissions. [ABSTRACT FROM AUTHOR]