Quantification of self pollution from two diesel school buses using three independent methods

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 PM 1 , 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 PM 2.5 inside the bus, respectively, with significantly higher crankcase self pollution (SP) when windows were closed. Approximately two-thirds of in-cabin PM 2.5 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.

Effects of heating season on residential indoor and outdoor polycyclic aromatic hydrocarbons, black carbon, and particulate matter in an urban birth cohort

“…One important finding to date from micro-environmental monitoring suggests that kindergarten-aged children who play inside and outside their school in a high traffic area may be exposed to inhalatory PAH levels up to six times higher than what may occur in less polluted areas (Fiala et al, 2001). Also, school bus emissions may be large sources of children’s daily exposure to diesel and other combustion emissions such as PM 2.5 , and elemental carbon (Adar et al, 2008; Sally Liu et al, 2010). Residential monitoring can be conducted for much longer durations and remains another useful option for assessing PAH exposures, especially in young children.…”

Adopting electric school buses in the United States: Health and climate benefits

“…However, these effects were observed in very old and polluting buses with few emission controls, and it is uncertain whether they apply to the current diesel bus fleet. Studies of pre-MY 2007 school buses have suggested that self-pollution contributed an average of 7 to 8 μg/m 3 to in-cabin PM 2.5 concentrations ( 60 – 62 ), an exposure as large as current average ambient PM 2.5 levels in the United States (7.8 μg/m 3 ) ( 63 ). However, 80% of this PM 2.5 self-pollution was estimated to come from crankcase emissions ( 61 , 62 ), which were allowed to be released unfiltered until MY 2007 ( 64 – 66 ).…”

“…Studies of pre-MY 2007 school buses have suggested that self-pollution contributed an average of 7 to 8 μg/m 3 to in-cabin PM 2.5 concentrations ( 60 – 62 ), an exposure as large as current average ambient PM 2.5 levels in the United States (7.8 μg/m 3 ) ( 63 ). However, 80% of this PM 2.5 self-pollution was estimated to come from crankcase emissions ( 61 , 62 ), which were allowed to be released unfiltered until MY 2007 ( 64 – 66 ). Uncertainty remains about self-pollution in newer buses, as well as about the share of older buses in the current fleet that have been retrofitted.…”