Environmental Engineering Reference
In-Depth Information
E
XAMPLE
6.20 E
FFECT OF
SO
2
O
XIDATION ON THE
pH
OF AN
O
PEN
S
YSTEM
(A
QUEOUS
D
ROPLET
)
THAT
C
ONTAINS
HNO
3
,NH
3
,H
2
O
2
,
AND
O
3
Consider an aqueous droplet with HNO
3
,NH
3
,H
2
O
2
,O
3
, and SO
2
as the main
constituents. The following initial conditions (
t
=
0) were chosen by Seinfeld and
Pandis(2005):[S(IV)]
total
=
5 ppb,[HNO
3
]
total
=
1 ppb,[NH
3
]
total
=
5 ppb,[O
3
]
total
=
5 ppb, [H
2
O
2
]
total
=
1 ppb, [S(VI)]
t
=
0
=
0, and water content
=
10
−
6
.
For an open system, we can assume that the partial pressures of the different species
remain constant. As S(IV) gets oxidized to S(VI), the new species of interest will com-
prise SO
2
−
4
and HSO
4
. We shall indicate
[
S(VI)
]=[
SO
2
−
]+[
HSO
4
]+[
H
2
SO
4
]
aq
.
4
The electroneutrality equation is
H
+
+
NH
4
HSO
3
+
2
SO
2
3
+
2
SO
2
4
HSO
4
NO
3
.
=
OH
−
+
+
+
6.2
6.0
5.8
Open system
5.6
5.4
5.2
Closed system
5.0
4.8
4.6
0
10
20
30
40
50
60
Time, min
FIGURE 6.37
pH as a function of time for both open and closed systems. The condi-
tions for the simulation are [S(IV)]
total
=
5 ppb, [NH
3
]
total
=
5 ppb, [HNO
3
]
total
=
1 ppb, [O
3
]
total
=
5 ppb, [H
2
O
2
]
total
=
1 ppb,
θ
=
10
−
6
,pH
o
=
6.17. (Reprinted
from Seinfeld, J.H. and Pandis, S.N. 1998.
Atmospheric Chemistry and Physics
,
p. 390. NewYork: Wiley. With permission.)
continued
Search WWH ::
Custom Search