Environmental Engineering Reference
In-Depth Information
4.4 Dependence on NO
2
-
and NO
3
-
Photolysis: Effect
of Wavelength Spectrum, Temperature, and pH
•
largely depends on the presence of NO
2
-
and NO
3
-
in natural waters (Zafiriou and True
1979a
,
b
; Takeda et al.
2004
;
(Zafiriou and Bonneau
1987
; Zepp et al.
1987
; Zellner et al.
1990
; Brezonik and
Fulkerson-Brekken
1998
; Mack and Bolton
1999
). The quantum yield of HO
The photoinduced generation of HO
•
(
Φ
HO
) for NO
2
-
and NO
3
-
photolysis significantly depends on the temperature,
wavelength and pH in the aqueous solution (Tables
4
and
5
) (Zepp et al.
1987
;
Zellner et al.
1990
; Goldstein and Rabani
2008
; Matykiewiczová et al.
2007
;
Treinin and Hayon
1970
; Strehlow and Wagner
1982
; Warneck and Wurzinger
1988
; Mark et al.
1996
; Vione et al.
2001
; Chu and Anastasio
2003
). The
Φ
HO
of NO
2
-
photolysis has been determined for a NO
2
-
concentration of 3
×
10
-3
M, for 4
≤
pH
≤
11 and temperatures between 278-353 K at 308 nm (Table
4
)
(Zellner et al.
1990
). The absorption coefficient of NO
2
-
at 308 nm is
ε
308
=
4.1
L mol
-1
cm
-1
(Strickler and Kasha
1963
). For the same solution,
Φ
HO
has also
been determined in the temperature range of 278-358 K, for pH 8 and under
351 nm irradiation (Table
4
). Note that the absorption coefficient of NO
2
-
is
ε
351
=
9.4 L mol
-1
cm
-1
(Strickler and Kasha
1963
). The results have demon-
strated that
Φ
HO
generally increases with temperature and decreases with pH
(Fig.
4
).
The temperature dependence of
Φ
HO
is mathematically derived, based on the
results of NO
2
-
photolysis at 308 (Eq.
4.8
) and 351 nm (Eq.
4.9
) at room tempera-
ture (Table
4
) (Zellner et al.
1990
). It can be expressed as:
(4.8)
Φ
HO
(
298 K
) =
0. 07
±
0. 01
for 7
≤
pH
≤
9
(4.9)
Φ
HO
(
298 K
) =
0. 046
±
0. 009
for pH
=
8
Using the averaged data over the range 7
≤
pH
≤
9, the temperature depend-
ence of
Φ
HO
at 308 nm (Eq.
4.10
) becomes:
1
T
1
298
−
Φ
HO
(
T
) = Φ
HO
(
298 K
)
exp
(
1560
±
360
)
(4.10)
where the apparent activation energy is
E
A
=
13
±
3 kJ mol
-1
. This equation is
in good agreement with previous data (Zafiriou and Bonneau
1987
), where it has
been obtained
E
A
=
12
±
6 kJ mol
-1
at 298.5 nm and in the temperature range of
296-322 K.
The temperature dependence of
Φ
HO
for NO
2
-
photolysis at 351 nm can be
expressed as (Eq.
4.11
):
1
T
1
298
−
Φ
HO
(
T
) = Φ
HO
(
298 K
)
exp
(
1800
±
400
)
(4.11)
