Environmental Engineering Reference
In-Depth Information
intake fractions, and understanding the spatial and temporal variability across a
population for individual intake fractions provides useful information about which
exposure factors dominate the inter-individual intake fraction variation.
Methodology
This study examines spatial distributions of benzene from local vehicular traffic, in
the Helsinki Metropolitan Area (HMA), using different methods of intake fraction
calculations. The first method incorporates both spatial and temporal information
on population activity patterns as spatial concentration distribution for 1 year, and
subsequently examine the spatial distribution of intake pattern in an urban area,
using the exposure model EXPAND model
[3]
. This model was further developed
to calculate iF for several substances. The spatial benzene concentration distribu-
tions were obtained by using dispersion models: CAR-FMI
[4]
and OSPM
[5]
. For
HMA CAR-FMI was used for the emission calculations and the results were com-
pared with previous studies conducted in HMA by
[6]
. OSPM was used for the
street canyon calculations in a segment of Hämeentie Street. The activity patterns
available for EXPAND are for HMA working age population (25-55 years old),
representing 46% of the whole HMA population
[3]
. The microenvironment activity
data in EXPAND is divided into four categories: home, workplace, traffic and other
activities. Note however, that EXPAND does not calculate an individual's personal
intake fraction, but rather the intake fraction per unit area, averaged over the number
of people that are located within that area for all or some portion of the averaging
time. Although several activities are comprised in the EXPOLIS database, the
EXPAND model accepts a single breathing rate only, so we assumed a constant rate
of 1 m
3
/h, based on the U.S. Environmental Protection Agency's (USEPA's) Exposure
Factors Handbook
[7]
. In order to include the air exchange rates between outdoor
and indoor, an infiltration efficiency of 0.8 for buildings
[8]
and 4 for vehicles
[9]
was used to calculate intake fractions for indoor environments, acknowledging that
concentrations inside vehicles are higher
[10]
.
The second method uses data from Air Pollution Exposure Distributions of
Adult Urban Populations in Europe (EXPOLIS) project to estimate intake fractions
for individuals in different environments. The data describes the adult population
between 25 and 55 years old when exposed to different pollutants, including benzene,
in different micro-environments: home, workplace and outdoor. Detailed descrip-
tions of the EXPOLIS study design and methods have been published previously
[11-13]
. We assume that the residual personal benzene exposure, not accounted for
by residential indoor, outdoor, and workplace exposures is due primarily to exposure
while commuting. Since EXPOLIS did not measure in-vehicle benzene concentra-
tions, individual intake fraction while commuting was estimated. The method to
calculate individual iF while commuting is described in
[14]
. An individual's intake
fraction is computed from:
