Geography Reference
In-Depth Information
52,000 trips were represented in this dataset. Among these individuals, only those
who resided in Franklin County and did not undertake any travel outside Franklin
County were included in this study. Data items in this dataset include personal and
household information such as age, gender, education, and race of each individual,
household income, vehicle ownership, and number of household members. Many
characteristics of the activities and trips participants undertook in an assigned survey
day are also included in the dataset, such as activity location (latitude and longitude)
and timing of activities and trips.
16.4
Method
Assessment of both static and dynamic exposure in this study was performed
through three procedures: (1) estimation of air pollution concentrations using
an air pollution dispersion model; (2) extrapolation and addition of monitored
concentrations; and (3) evaluation and comparison of individual exposures using
both static and dynamic measures. These procedures were implemented using an air
dispersion modeling software package (BEEST Suite) and ArcGIS 9.2.
16.4.1
Estimation of Particulate Concentrations
To estimate air pollution dispersion, this study used a Gaussian plume model in
which air pollution is represented as a plume coming from the top of a stack (point
source) characterized by a height and diameter. The vertical displacement of the
plume is determined from the stack dimensions along with stack gas exit velocity
and temperature. After the plume has reached the stack height, the pollution is
dispersed in three dimensions. This model was implemented using the Industrial
Source Complex Short Term 3 (ISCST3) model in the BEEST Suite and the
following Gaussian equation:
2 U
s
y
z
exp
"
2
#
0:5
y
y
QKVD
X
D
where:
Q
D
pollutant emission rate (mass per unit time)
K
D
a scaling coefficient to convert calculated concentrations to desired units
(default value of 1
10
6
for Q in g/s and concentration in g/m
3
V
D
vertical term for source elevation, receptor elevation, plume rise, etc.
D
D
decay term
y
,
z
D
standard deviation of lateral and vertical concentration distribution (m)
U
s
D
mean wind speed (m/s) at release height
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