243
Photoinduced Generation of Hydroxyl Radical in Natural Waters
These results allow the hypothesis that the temperature dependence of Φ HO for
NO 2
– photolysis is independent of wavelength, despite a decline of the absolute
Φ HO value with increasing wavelength (Fig. 4) (Zellner et al. 1990).
On the other hand, the Φ HO of NO 3
– photolysis has been determined for
a NO 3
– concentration of 3 × 10 –3 M in the range 4 ≤ pH ≤ 11, at temperature
between 278–353 K and 308 nm irradiation (Table 5) (Zellner et al. 1990). The
absorption coefficient of NO 3
– at 308 nm is ε 308 = 6.5 L mol –1 cm –1 (Meyerstein
and Treinin 1961). It has been shown that the quantum yields at each temperature
are generally independent of pH in the range 4 ≤ pH ≤ 9. At higher pH’s, the
quantum yield is typically decreased (Fig. 5).
0.02
0.06
0.1
0.14
0.18
278 288 298 308 318 328 338 348 358
pH 8
Temperature (K)
0.02
0.06
0.1
0.14
0.18
278
298
318
353
pH 4
pH 5
pH 6
pH 7
pH 8
pH 9
pH 10
pH 11
Φ
HO at various pHs
Fig. 4 Quantum yields of HO
• of NO 2
– photolysis with variation in temperature at a specific
wavelength at 308 nm for various pH (a) and at 351 nm (b) at pH 8. Data source Zellner et al.
(1990)
Fig. 5 Quantum yields of
HO
• of NO 3
– photolysis with
variation in temperature at a
specific wavelength (308 nm)
for various pH. Data source
Zellner et al. (1990)
0
0.011
0.022
0.033
0.044
278
2 98
318
353
pH 4
pH 5
pH 6
pH 7
pH 8
pH 9
pH 10
pH 11
Φ
HO at various pHs
Temperature (K)