Environmental Engineering Reference
In-Depth Information
TABLE 9.6
Optimized Sulfate Deposition
Model Parameters
Parameter
Optimized Value
4.3E(6) m
2
s
−
1
D
h
7.1 m s
−
1
u
214
◦
δ
τ
c
1.9E(5) s
τ
wp
11.3E(5) s
τ
ws
0.6E(5) s
τ
dp
2.0E(5) s
τ
ds
12.5E(5) s
Data from Fay J. A., D. Golomb, and S. Kumar, 1985.
Atmos.
Environ.,
19,
1773-1782.
Using optimized model parameters, source receptor distance, and azimuthal angle, wet (and
dry) deposition rates at any receptor due to any source in ENA can be estimated. Instead of using
individual sources, such as a single power plant, it is convenient to aggregate sources within a
whole state by assigning an “emission centroid” to that state. Using state-level emission rates of
SO
2
in 31 states east of the Mississippi River, along with observed annual wet sulfate deposition
rates at tens of stations in ENA in 1980-1982, the predicted and observed wet sulfate deposition in
ENA is presented in Figure 9.11. The observed data points are printed at the approximate location
of the stations. The modeled values are represented by the isocontours. The deposition rates are in
units of kg SO
2
4
per hectare per year. It is seen that a good match is obtained, with a correlation
coefficient of 0.88 and an error of 17%, as defined in equation (9.27). Like the hydrogen deposition
in Figure 9.9(b), the isocontours are stretched toward the northeast because of the prevailing
southwesterly winds.
9.2.6.2 Transfer Coefficients
A transfer coefficient
T
ij
is defined as the ratio of annual wet sulfate deposition at the receptor
j
to the annual SO
2
emission from source
i
. It is derived from equations (9.21)-(9.24) by vary-
ing the source-receptor distance and the angle subtended between the source receptor line and
the prevailing wind. Transfer coefficients for ENA are plotted in Figure 9.12 for three angles:
(a) receptor lying directly downwind; (b) receptor lying crosswind; and (c) receptor lying upwind.
The units on the
y
axis are ha
−
1
.IfSO
2
emissions are given in kg y
−
1
, depositions of SO
−
4
are
obtained in units of 1.5 kg ha
−
1
y
−
1
. (The factor 1.5 arises because the ratio of molecular weight
SO
2
4
/SO
2
is 1.5.) The amount of wet sulfate deposition at receptor
j
from all sources
i
is obtained
from
T
ij
Q
i
i
D
j
w
=
(9.28)
s
where
Q
i
is the annual SO
2
emission at source
i
.
