Environmental Engineering Reference
In-Depth Information
seawater (Johnson et al.
1989
; Sakugawa et al.
2000
; Sikorsky and Zika
1993a
,
b
; Scully et al.
1998
). Similarly the vertical convective overturn, which is usu-
ally caused by nocturnal cooling in the upper lake or ocean, may greatly decrease
the surface H
2
O
2
concentration through distribution in the whole water column
(Johnson et al.
1989
; Sarthou et al.
1997
; Yuan and Shiller
2001
).
4.8 Salinity Effect on Production of H
2
O
2
The photoproduction of H
2
O
2
significantly increases with salinity in natural
waters (Osburn et al.
2009
). The generation of H
2
O
2
upon irradiation of ultrafil-
tered river DOM substantially increases from 15 to 368 nM h
−
1
with increasing
salinity at circumneutral pH values (Osburn et al.
2009
). The increase in H
2
O
2
production with salinity has a linear trend (Eq.
4.10
) (Osburn et al.
2009
):
r
2
=
0
:
99,
p
=
0
:
001,
n
=
10
H
2
O
2
(
nM
) =
83. 15
×
salinity
−
69. 16
(4.10)
The apparent quantum yield of H
2
O
2
photoproduction from ultrafiltered river
DOM,
Qhp
, also increases with salinity from 1.64
×
10
−
4
to 37.02
×
10
−
4
(Osburn et al.
2009
).
The mechanism of high production of H
2
O
2
with salinity is not well docu-
mented in ealier studies. It is hypothesiszed that hydrated electrons (e
aq
−
) are con-
siderably formed in ionic (saline) solution under irradiation. This phenomenon can
substantially increase the production of superoxide radical (O
2
•
−
) and, through
disproportionation, of H
2
O
2
in aqueous solution. This is evidenced by the pho-
toinduced formation of aqueous electrons (e
aq
−
) from organic substances and by
their high production in NaCl-mixed solutions compared to pure (Milli-Q) water
(Fujiwara et al.
1993
; Gopinathan et al.
1972
; Zepp et al.
1987b
; Nakanishi et
al.
2002
; Assel et al.
1998
; Richard and Canonica
2005
). In the presence of high
salinity it was also observed a significant increase of CDOM loss (10-40 %) and
high photoelectrochemical degradation of methyl orange (~48 % increase in 0.5 M
NaCl) (Osburn et al.
2009
; Zhang et al.
2010
). The mechanisms behind the high
photoinduced reactivity of DOM with salinity are discussed in details in other
chapters (see chapters
“
Colored and Chromophoric Dissolved Organic Matter in
4.9 Production Affected by Precipitation
Precipitation in the form of e.g. rain greatly increases the peroxide concentra-
tions in natural waters (Sakugawa et al.
1995
; Avery et al.
2005
; Cooper et al.
1987
; Yuan and Shiller
2000
). This might be caused by the mixing of highly
