(VCCEP) Tier 1 Pilot Submission for BENZENE - Tera

In-Vehicle Exposures
In-vehicle exposure to benzene is due to the penetration of benzene in roadway air (e.g.,
tailpipe emissions) and from engine running loss into the vehicle cabin while driving (Graboski et
al., 1998 Chan et al., 1991b). It should be noted however, that at least one investigator
suggested that there is only a weak relationship between benzene content in gasoline and
benzene concentration from tailpipe emissions (Wallace, 1996). In-vehicle benzene exposure
occurs exclusively via inhalation. In-vehicle VOC exposure levels can be affected by various
conditions including mode of transportation, driving route, time of day (rush vs. non-rush), type
of fuel distributions system, season of the year, meteorological conditions and vehicle ventilation
conditions (Chan et al., 1991a,b; Dor et al., 1995; Lawryk and Weisel, 1996; Batterman et al.,
2002; Fedoruk and Kerger, 2003). In many cases, the findings of the various studies can be
conflicting, and in-vehicle VOC concentrations can vary considerably with sampling day and
time (Lawryk et al.,1995; Batterman et al., 2002).
Of all modes of transportation involving potential non-occupational exposure to gasoline
constituents (e.g., automobile, bus, subway, walking, biking), in-vehicle exposures while driving
in an automobile are the highest (Chan et al., 1991a). Although many children commute in
school buses, studies show that because of variables including vehicle height, location of
engine, ventilation conditions and fuel type, exposure in a car is greater (Chan et al., 1991a; Jo
and Choi, 1996; Jo and Park, 1998; 1999a,b; Jo and Yu, 2001) or the same (Batterman et al.,
2002) as that of a bus. The transportation route and traffic density (e.g., urban or rural, following
closely or far behind a lead car, rush or non-rush) have been determined to be the most
important in-vehicle exposure variables (Batterman, et al., 2002). It is expected that in-vehicle
exposures in suburban areas, rural areas and in general, areas with lower automobile densities,
will have lower in-vehicle concentrations.
Numerous studies have been conducted in the U.S., which have evaluated in-vehicle benzene
exposures (SCAQMD et al., 1989; Chan et al., 1991a,b; Weisel et al., 1992; Lawryk et al., 1995;
CARB, 1998b; Chang et al., 2000, Fedoruk and Kerger, 2003; Batterman et al., 2002). Due to
the emission reduction and fuel-changing initiatives discussed above, only the most recent U.S.
data were included in this analysis. Although the CARB, 1998 study is relatively recent, it was
excluded because the study design required evaluation of highly unusual and unrealistic
conditions (i.e., travel behind a high emitting vehicle for 2 hours). It is unlikely that a driver
would closely tail a high-emitter during the entirety of his or her driving time. It is more likely that
the driver would move from behind such a vehicle, and would be behind a variety of vehicles
while driving during any given time period. The studies used to derive representative exposure
concentrations are summarized in Table 7.29 below. Each of the automobile studies evaluated
specifically excluded smokers and/or the influence of smoking on VOC in-vehicle
concentrations.
Benzene VCCEP Submission
March 2006
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