Environmental Engineering Reference
In-Depth Information
Fig. 4.2 Acid rain formation mechanism [
7
]
The regional increase of atmospheric pH is generally caused by terrestrial
ammonia sources, among which the most important are agriculture and animal
breeding [
11
].
The presence of ammonia can have a beneficial influence as a result of the
neutralisation of free acidity in the air; at the same time, in higher atmospheric
layers, with the contribution of solar energy, through oxidation reactions catalyzed
by heavy metal compounds such as TiO
2
under the form of nanoparticles, ammonia
can take different forms of NO
x
[
12
]:
2NH
3
þ
ð
2
x
þ
3
Þ
O
!
2NO
x
þ
3H
2
O
ð
4
:
12
Þ
The reaction of ammonia oxidation in the atmosphere is slow and plays only a
minor role in reducing its concentration. The experimental data obtained for
ammonia from the series of oxidation reactions under normal atmospheric condi-
tions are based on kinetic models with elements of intermediary accumulation, as
the oxidation reactions occur simultaneously with ammonia generation in the
atmosphere, through the mass transfer processes that control the kinetics of parallel
chemical and biochemical reactions [
13
].
The conversion and reconversion of nitrogen compounds to different oxidation
states is a much more complicated process, because the reactions also involve
atmospheric nitrogen, electrical phenomena, the soil and the biosphere with all its
life forms capable of producing the nitrification-denitrification reactions that char-
acterise the circulation of nitrogen in nature [
13
-
15
].
