Māris kļaviņŠ, azamat azizov, JĀnis zaļoksnis environment, pollution, development: the case of uzbekistan

 5.3.2.  Nitrogen compounds
Nitrogen(I) oxide N
2
O is formed mainly through natural 
processes, and human activity affects its concentration only indirectly. 
This substance is odourless, tasteless and chemically inert. It is used as 
an anaesthetic agent in medicine and as an inert gas in technological 
processes. No toxic effects of this substance have been found.
From the environ mental pollution standpoint, special attention 
should be given to nitrogen(II) oxide NO and nitrogen(IV) oxide 
NO
2
. Nitrogen(II) oxide NO is a colourless, odourless and non-
flammable gas. Since it is easily oxidised to NO
2
 in the air, usually 
the combination of these two oxides resulting in NO
x
 or flue gas is 
considered. Nitrogen(II) and nitrogen(IV) oxides are highly toxic. 
Nitrogen(II) oxide is formed when the gases constituting the atmo-
spheric air mutually react at increased temperatures. The rate of this 
Nitrogen makes up 
approximately 76% of the 
mass of the atmosphere. 
Several nitrogen oxides 
can also be present in the 
atmosphere as air pollu‑
tants: nitrogen(I) oxide 
N
2
O, nitrogen(II) and (IV) 
oxides NO, NO
2
 and even 
nitric acid HNO
3
.

---

90 
ENVIRONMENT, POLLUTION, DEVELOPMENT:  THE CASE OF UZBEKISTAN
reaction depends on the temperature, respectively, on the amount of 
energy supplied. NO is already forming, for example, when reaching 
incandescence. The reaction of NO, N
2
 and O
2
 molecules is in a state 
of equilibrium at a temperature of 2000 °C. The intensity of the NO 
formation process is affected by how soon the created molecule 
leaves the reaction zone. In any case, nitrogen oxides are formed in 
all processes that take place at high temperatures, e.g. in plasma and 
in combustion and explosion processes.
Nitrogen oxides are also formed in the combustion processes 
of motor vehicle engines. Intensive release of nitrogen oxides 
during  the  process  of  electrical  welding,  especially  in  confined 
premises, is unsafe from the viewpoint of work safety. Emitted in the 
stratosphere, nitrogen oxides can participate in the ozone breakdown 
cycle. Supersonic aircraft exhaust is a significant source of nitrogen 
oxides in the stratosphere.
The oxidation of nitrogen oxides in the atmo sphere forms nitric 
acid HNO
3
, fallout of which occurs with precipitation mainly in the 
forms of acid and salt. Nitric acid, together with sulphur compounds, 
causes the acidification of precipitation and the environ ment. Since 
the transformations of nitrogen oxides and their elimination from 
the atmo sphere occur quite swiftly, the acidification of precipitation 
caused by nitrogen compounds significantly affects the areas near 
the contamination sources.
Today the emission of nitrogen oxides as well as another environ-
mental pollutant – ammonia – has become, overall, one of the most 
hazardous  environ mental  pollution  factors  in  Europe.  Although 
the emission levels have been notably reduced, they are still high 
(Figure 5.16).
The issue concerning the reduction and control of the emission 
of nitrogen oxides becomes particularly acute in the Baltic Sea 
Region countries, where the concentrations of nitrogen compounds 
stimulate many negative processes occurring in the region.
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
1990
1992
1994
1996
1998
2000
2002
2004
2006
Emission, thousand tons
NH
3 
emissions
NO
x 
emissions