(VCCEP) Tier 1 Pilot Submission for BENZENE - Tera

chemicals where there appeared to be a possible impact, the indoor and outdoor differences did
not translate into significant differences in personal exposure levels between the two
communities.
Inhalation of benzene in outdoor and indoor air was evaluated for each childhood age grouping
and the prospective parents. For ambient outdoor air, both urban and rural settings were
considered. For indoor air, both in-home and in-school exposures were considered.
7.2.1.2 Ambient Outdoor Air
General urban and rural ambient air concentrations of benzene were obtained from EPA's
National Air Toxics Assessment (NATA) database (EPA, 1996). This national-scale
assessment was conducted in 1996 for 33 air pollutants, including benzene. NATA compiled
the 1996 national emissions inventory of air toxics emissions from outdoor sources, and
estimated ambient concentrations using the ASPEN air dispersion model.
The NATA database was designed to help EPA, state, local and tribal governments and the
public better understand air toxics in the U.S. It is comprised of data from the following primary
sources of data for the NATA database:
• State and local toxic air pollutant inventories;
• Existing databases related to EPA’s air toxics regulatory program;
• EPA’s TRI database;
• Estimates developed by EPA’s Office of Transportation and Air Quality using
mobile source methodology; and
• Emission Estimates generated from emissions factors and activity data.
As compared to random measured concentrations in various literature studies, the NATA
database is a comprehensive ambient air database that is representative of the US, and the
various US counties. It provides a nationwide average as well as provides urban and rural
averages. Although there are uncertainties inherent in the database, benzene has the highest
confidence of all of the air pollutants. An EPA comparison of the estimated NATA benzene
concentrations to actual data from monitoring sites indicated a relatively good agreement
between the two. In general, for all pollutants, the NATA data erred on the low side when
compared to exact monitoring locations, but at greater distances (e.g. 10 – 20 km), the modeled
concentrations appeared to be in better agreement. For benzene, 89% of the modeled
concentrations were within a factor of 2 of the actual concentrations at monitoring sites.
Queries for “all urban counties” and “all rural counties” were run and the results are presented in
Table 7.3 below.
Benzene VCCEP Submission
March 2006
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