(VCCEP) Tier 1 Pilot Submission for BENZENE - Tera

Table 7.3: Outdoor Ambient Air Benzene Concentrations from NATA 1996
NATA Query Setting Utilized
Benzene VCCEP Submission
March 2006
Median
(µg/m 3 )
102
Mean (µg/m 3 )
95 th Percentile
(µg/m 3 )
Nationwide Nationwide 1.21
1.39
2.8
All Urban Counties Urban 1.41 1.57 3.0
All Rural Counties Rural 0.66 0.72 1.2
Texas Harris County 2.1 2.3 3.3
New York New York County 4.8 5.4 9.3
In determining a representative ambient outside air concentration for the child and prospective
parents, the NATA database mean values of 1.57 µg/m 3 for an urban setting and 0.72 µg/m 3 for
a rural setting have been selected. The mean concentrations were selected as they are
reasonable estimates of concentrations likely to be contacted over time (EPA, 1989). It should
be noted that the NATA results represent modeled ambient air concentrations from emissions
data collected in 1996 1 and thus may not reflect the potentially significant emission reductions
that have taken effect in the last ten years, including those from: 1) mobile source regulations
which are being phased in over time; 2) many of the air toxics regulations that EPA has issued
for major industrial sources; 3) state or industry initiatives; and 4) any facility closures (EPA,
1996). Because of this, the NATA concentrations listed on Table 7.3, may overestimate the
current national averages. For example, Kinney et al. (2002) conducted an air monitoring study
in New York City during 1999 to characterize levels and factors affecting exposure to benzene.
This study reported benzene concentrations 2.8 times lower than the NATA 1996 modeled
mean concentrations for New York County.
Although Wallace and more recently, Buckley et al., have concluded that industrial sources of
benzene are not important with regards to personal benzene exposures on a nationwide basis
(Wallace, 2001; Buckley et al. 2005), potential benzene exposures were evaluated for those
living in close proximity to the highest industrial benzene emitters in urban and rural locations.
For such residents, the NATA data and that from individual air monitoring stations can be used
to understand the potential differences in benzene exposure a child might receive from outdoor
air if residing in close proximity to an industrial source. For this exposure assessment, the top
five TRI reporting facilities for benzene air releases were evaluated. The currently available TRI
release data are for reporting year 2003. The TRI was queried to identify the top five urban and
rural benzene air emitters, which are listed on Table 7.4.
1 Since the time of this analysis, the EPA released an updated NATA using the 1999 emissions inventory.
The updated NATA for benzene indicated that the predicted 1999 ambient air concentrations of benzene
nationwide and for the ‘all urban’ and ‘all rural’ counties were similar to the 1996 modeled estimates.