Characterizing the range of children's air pollutant exposure during school bus commutes

Abstract

Real-time and integrated measurements of gaseous and particulate pollutants were conducted inside five conventional diesel school buses, a diesel bus with a particulate trap, and a bus powered by compressed natural gas (CNG) to determine the range of children's exposures during school bus commutes and conditions leading to high exposures. Measurements were made during 24 morning and afternoon commutes on two Los Angeles Unified School District bus routes from South to West Los Angeles, with seven additional runs on a rural/suburban route, and three runs to test the effect of window position. For these commutes, the mean concentrations of diesel vehicle-related pollutants ranged from 0.9 to 19 mg/m 3 for black carbon, 23 to 400 ng/m 3 for particle-bound polycyclic aromatic hydrocarbon (PB-PAH), and 64 to 220 mg/m 3 for NO 2 . Concentrations of benzene and formaldehyde ranged from 0.1 to 11 mg/m 3 and 0.3 to 5 mg/m 3 , respectively. The highest real-time concentrations of black carbon, PB-PAH and NO 2 inside the buses were 52 mg/m 3 , 2000 ng/m 3 , and 370 mg/m 3 , respectively. These pollutants were significantly higher inside conventional diesel buses compared to the CNG bus, although formaldehyde concentrations were higher inside the CNG bus. Mean black carbon, PB-PAH, benzene and formaldehyde concentrations were higher when the windows were closed, compared with partially open, in part, due to intrusion of the bus's own exhaust into the bus cabin, as demonstrated through the use of a tracer gas added to each bus's exhaust. These same pollutants tended to be higher on urban routes compared to the rural/suburban route, and substantially higher inside the bus cabins compared to ambient measurements. Mean concentrations of pollutants with substantial secondary formation, such as PM 2.5 , showed smaller differences between open and closed window conditions and between bus routes. Type of bus, traffic congestion levels, and encounters with other diesel vehicles contributed to high exposure variability between runs.

Determinants of ultrafine particle exposures in transportation environments: findings of an 8-month survey conducted in Montréal, Canada

“…Unfortunately, quantitative ventilation measures were not collected in buses or the automobile and more controlled exposure scenarios may be required for a comprehensive exploration of the effect of window opening on bus and automobile UFP exposures. Nevertheless, it seems likely that closed windows may reduce traffic-related UFP exposures in buses and automobiles, particularly during encounters with large diesel vehicles which can result in substantial increases in cabin pollutants when windows are open Sabin et al, 2005). In this respect, findings from the current study are consistent with those of previous investigations Sabin et al, 2005) as dramatic increases in bus and automobile UFP levels were observed while driving past a coach passenger bus with the windows open (Figure 2b and c).…”

“…Nevertheless, it seems likely that closed windows may reduce traffic-related UFP exposures in buses and automobiles, particularly during encounters with large diesel vehicles which can result in substantial increases in cabin pollutants when windows are open Sabin et al, 2005). In this respect, findings from the current study are consistent with those of previous investigations Sabin et al, 2005) as dramatic increases in bus and automobile UFP levels were observed while driving past a coach passenger bus with the windows open (Figure 2b and c). However, other studies exploring the effects of window opening on UFP counts in buses or automobiles were not identified.…”

In-Vehicle Exposures to Particulate Matter and Black Carbon

“…18 BC, particlebound polycyclic aromatic hydrocarbon (PB-PAH), benzene, and formaldehyde concentrations were all higher as a result of introduction of own exhaust when a school bus's windows were closed. 19 BC, PB-PAH, and benzene levels were higher in a conventional diesel bus than in one using compressed natural gas (CNG), although formaldehyde levels in the CNG bus was higher. 19 The purpose of this study was to identify determinants of in-vehicle PM number and BC concentrations in a transportation microenvironment.…”

Towards an interdisciplinary science of transport and health: a case study on school travel

“…Season, route and ventilation of the vehicles (e.g. open windows) all influence the level of exposure (Lee and Jo 2002;Sabin et al 2005;Zhu et al 2007;Zuurbier et al 2010). The interactions between these factors are likely to contribute to the inconsistencies observed in exposures associated with different transport modes described above.…”