by Lisa D. Sabin, Eduardo Behrentz, Arthur M. Winer, Seong Jeong, Dennis R. Fitz, David V. Pankratz, Steven D. Colome And Scott A. Fruin
Although ambient air pollution contributes to adverse health effects, exposure to the highest concentrations of many air contaminants occurs in other microenvironments, such as vehicles. Roadways and sidewalks have been shown to exhibit the highest outdoor concentrations for many air pollutants and elevated concentrations of elemental carbon and polycyclic aromatic hydrocarbons (PAH) have been recorded in tunnels and on heavily traveled roadways (Benner et al., 1989; Venkataraman et al., 1994; Kirchstetter and Harley, 1999). In-vehicle concentrations have been shown to be higher than those measured at fixed site monitors and in some cases higher than those measured along roadways (Shikiya et al., 1989; Ptak and Fallon, 1994; Lawryk and Weisel, 1995; Rodes et al., 1998; Alm et al., 1999). However, although a number of studies have investigated exposure to air pollutants inside vehicles, the majority of these focused on passenger cars and pollutants predominantly emitted by them (carbon monoxide and volatile organic compounds), and few focused on dieselrelated pollutants such as particulate matter (PM), particlebound PAH (PB-PAH) or black carbon.
As children are more susceptible to adverse health effects from air pollution (Lipsett, 1989; Wiley et al., 1991), potentially high pollutant exposures during school bus commutes are of concern, but few studies have attempted to characterize concentrations on board school buses. Solomon et al. (2001) investigated the concentrations of PM2.5 and black carbon inside four diesel school buses in the Los Angeles area, including measurements inside and outside buses, Received 16 March 2004; accepted 27 October 2004 and in a passenger car traveling ahead of the bus. They reported levels of black carbon inside the bus increased when all windows were closed and decreased with windows open, and were higher in the back of the bus compared to the front. They concluded the level of black carbon in the back of a school bus with windows closed could be up to four times higher than in a passenger car ahead of the bus.
Wargo et al. (2002) reported concentrations of black carbon and PM2.5 inside commuting diesel school buses in rural Connecticut were often 5–10 times higher than background concentrations. They found several important variables affected the concentrations of pollutants inside school buses, including bus ventilation via windows, bus idling behavior, and outdoor concentrations on bus routes. They also tested a school bus fueled with natural gas and observed 60–98% less black carbon on board than on diesel-powered buses.
In the present study, we investigated the range of exposures experienced by children during commutes on different types of school buses (e.g. conventional diesel, particle trapoutfitted diesel and natural gas) and bus routes, and identified factors leading to higher exposures.
July 14, 2008