Environmental Engineering Reference
In-Depth Information
EPA-recommended dispersion models. For
unstable
and
neutral
conditions we have
71
F
3
/
5
u
−
1
h
=
38
.
(9.4)
where the numerical factor 38.71 has the dimensions
s
4
/
5
m
−
2
/
5
, where the buoyancy flux parameter
F
is
v
s
D
s
(
F
=
g
T
s
−
T
a
)/
4
T
s
(9.5)
and where
acceleration of gravity (9.8 m s
−
2
)
v
s
=
g
=
flue gas stack exit velocity, m s
−
1
D
s
=
stack diameter, m
T
s
=
flue gas exit temperature, K
T
a
=
ambient temperature at stack height, K
wind speed at stack height, m s
−
1
u
=
For
stable
conditions we have
)
−
1
]
1
/
3
h
=
2
.
6[
F
(
uS
(9.6)
where the numerical factor 2.6 has the dimension m
2
, where
S
is the atmospheric stability parameter
T
−
1
a
S
=
g
(δθ/δ
z
)
(9.7)
δθ/δ
and where
z
is the potential temperature gradient, whose value is 0.02 K/m for category E and
is 0.035 K/m for category F.
4
9.2.4.4 Steady-State Line Source
A line source pertains to a situation where point sources are aligned in a row, such as several smoke
stacks along a river bank, or many automobiles and trucks traveling in both directions along a
straight highway. The geometry of a line source is depicted in Figure 9.4. The ground level mass
concentration
c
(
x
)
is estimated by the following variant of the GPE
H
2
σ
2
Q
l
1
2
c
(
x
)
=
exp
−
(9.8)
1
/
2
z
(
2
π)
σ
z
u
sin
φ
where
average line source mass emission rate per meter, g m
−
1
s
−
1
Q
l
=
H
=
average release height from sources, m
4
Equation (9.4) is only applicable for a buoyancy parameter
F
>
55 m
4
s
−
3
. For
F
≤
55 m
4
s
−
3
, and unstable
or neutral conditions
h
=
21
.
425 F
3
/
4
u
−
1
.
