(VCCEP) Tier 1 Pilot Submission for BENZENE - Tera

factor change attributable to benzene content decreases in gasoline and those attributable to
fleet emission control improvements. A detailed description of the methods used to derive the
NF is presented in Appendix A.
The NF ranged from 1.07 to 1.24, depending on whether it was assumed that there were only
cars in the garage, a mix of cars and small engine sources or small engines only. When the NF
is applied to the measured air concentrations from Adgate et al. (2004b), the normalized
concentrations ranged from 7% reduction in benzene concentrations for homes with small
engines only in the garage to 18% reduction in homes with small engines and cars in the
garage.
Based on this analysis, it is believed that the indoor air concentrations used in this assessment
are conservative (i.e. exposure enhancing) estimates of children’s exposure. Future residential
indoor air studies will likely show that benzene air concentrations are lower than those used in
this analysis.
7.2.1.5 Alaskan Indoor Air Studies
Several attached garage studies that measured benzene levels in indoor air have been
conducted in Alaska (Isbell et al., 1999, Schalapia and Morris, 1998, and Morris 2004). The
benzene measurements from these studies are provided in Table 7.12.
The indoor air concentrations of benzene measured in the Alaskan studies have been higher
than those measured in the other attached garage studies (See Table 7.11). Also of note, Isbell
et al. (1999) found that the reported concentrations were strongly correlated to the number of
small engines stored in the garage and whether the home had a forced ventilation system or
ventilated naturally via the building shell, windows and doors (Isbell, et al., 2005).
Several factors are believed to be related to these higher observed values. The benzene
content of conventional gasoline produced in the lower 48 states is roughly 1% - well below the
regulatory (Complex Model) limit of 5%. Due to equipment and demand limitations on refining
operations, gasoline produced in Alaska generally contains higher levels than in the lower 48
states, ranging from 2.2 – 4.5% in the three indoor air studies conducted. It should be noted that
although the benzene content in Alaskan gasoline is higher than that in the lower 48 states,
levels have recently been declining and have dropped approximately a percentage point from
2002 (3.2 – 3.6%) to 2005 (2.3 – 2.8%) (AAM 2002-2005). Another probable reason that the
Alaskan indoor air levels are higher is that the homes and garages are believed to have better
insulation and lower air exchange rates. Based on these data, children in Alaska may be
exposed to higher indoor air levels of benzene than the remainder of the U.S.
Benzene VCCEP Submission
March 2006
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