Page 356 - Air pollution and greenhouse gases from basic concepts to engineering applications for air emission control

334 11 Air Dispersion

Solution
First, determine the atmosphere stability using the Pasquill stability class described
in Table 11.1. It can be determined as class C stability. Note that this is still an
approximation because we are considering the wind speed to be uniform, which
may not be not the case in reality.
Anyways, with the class C stability the corresponding air dispersion coefficients
for rural area can be calculated using the equations in Table 11.4 as follows.

0:11x 0:11 5000
r y ¼ ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffip ¼ p ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ¼ 449:1m
1 þ 0:0001x 1 þ 0:0001 5000
0:08x 0:08 5000
r z ¼ ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffip ¼ p ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ¼ 282:8m
1 þ 0:0002x 1 þ 0:0002 5000

(a) The concentration at the plume center 5 km downwind can be determined
using Eq. (11.33) with z-H = 0 and y =0

_ m
Cx; 0; HÞ ¼
ð
2pr y r z u
0:1 8 3 3
¼ ¼ 2:09 10 ðkg=m Þ¼ 20:9ðlg=m Þ
2p 449:1 282:8 6
(b) The concentration on the ground right below the plume center at x = 5000 m
downwind is calculated using Eq. (11.33) with z =0, y = 0 and H = 120:

_ m H 2
ð
Cx; y; zÞ ¼ exp
2pr y r z u 2r 2 z
" #
2
1 120 3
¼20:9 exp ¼ 20:9 0:914 ¼ 19:1ðlg=m Þ
2 282:8
(c) The concentration at the ground right below the plume center at 2,000–6,000 m
downwind is calculated using Eq. (11.33) with z =0, y = 0 and H = 120:

_ m H 2
Cx; y; zÞ ¼ exp
ð
2pr y r z u 2r 2 z
where

0:11x
r y ¼ p ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
1 þ 0:0001x
0:08x
r z ¼ p ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
1 þ 0:0002x