Environmental Engineering Reference
In-Depth Information
included in the aqueous chemical mechanism. The exchange of chemical species
between the gas phase and the aqueous phase is considered following Schwartz
(1986).
3. Theoretical Studies on Transition Metal Ion Chemistry
These theoretical studies allow evaluating the role of TMI chemical reactions on,
for instance, the concentrations of radicals (HO
x
) and also on pollutants such as
nitric acid, VOCs, sulphate (Deguillaume et al., 2004; Deguillaume et al., 2005a).
Sensitivity analysis allows evaluating cloud chemistry pathways that are still
uncertain such as for example the Fenton reaction which is commonly considered
as source of OH radicals (Deguillaume et al., 2005b).
5.0x10
-7
6.0x10
-7
Fe(II)
Fe(III)
Fe(III)-Oxalate
Oxalate
Fe(II)
Fe(III)
4.0x10
-7
4.0x10
-7
3.0x10
-7
2.0x10
-7
2.0x10
-7
10
-7
0.0x10
0
0.0x10
0
0
6
12
18
24
0
6
12
18
24
Time (h)
Time (h)
Fig. 1.
Iron speciation including C1 chemistry (left handside), including C2 chemistry (right
handside)
The organic chemistry has been extended to two atom carbon chemistry (C2)
(Herrmann et al., 2005). This mechanism is evaluated following an idealistic
scenario describing remote conditions with simplified microphysics (duration: 24 h;
LWC: 0.3 g/m
3
; T°: 288.15 K, P: 1,000 hPa and the droplet radius: 10 μm). In Fig.
1,
we observe that including C2 chemistry results in a change in Fe(II)/Fe(III)
speciation due to the continuous production of oxalate resulting from the oxidation
of VOCs with C2 compounds. Indeed, the Fe(III) species is complexed by oxalate
and then less iron is available for the H
x
O
y
chemistry (Deguillaume et al., 2005b).
Therefore, the C2 mechanism leads to a depletion of the OH and nitrate radical
concentrations (mainly because of VOCs degradation), to an aqueous organic
species production (methanol, oxalic acid, acetic acid) and an increase of gaseous
and aqueous H
2
O
2
.
