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

particles into the atmo sphere as a result of wind activity, dust storms, 
volcanic eruptions, forest fires, evaporation from the sea and ocean 
surface (salt sprays or aerosols are formed). However, modern human 
behaviour results in a large amount of aerosols and dust in the air. 
The processes such as energy production, construction material 
production and mining, agriculture, air transportation and other are 
the main anthropogenic sources (Table 7.6).
Table 7.6. 
Sources of aerosol and dust emission 
Sources
10
6
 t/per year
Natural
Sea salts
1000
Soil
200
Volcanoes
4
Forest fires
3
Anthropogenic
Coal combustion
36
Oil combustion
2
Wood incineration
8
Waste incineration
4
Agriculture
10
Manufacture of cement
7
Manufacture of iron / steel 
9
Other
16
Aerosols can be formed, and the content of particles in the air 
may change due to a variety of chemical reactions. In this context 
the first to be mentioned is the important role of sulfur and nitrogen 
oxides in these processes. Since the airborne solid matter particles 
serve as condensation centres for water vapour, virtually all of these 
reactions take place in the aquatic environ ment or in the presence of 
water, and the typical examples of these are related to the formation 
of acid rain.
Aerosol formation under the influence of atmo spheric air is also 
affected by a number of mechanisms and physical processes:
1. Coagulation and sedimentation. The smallest of aerosol particles 
can stick together to form larger aggregates. This process affects 
the stability of aerosols and dust, and the time it stays in the 

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7. AIR POLLUTION
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atmosphere.  Particles  with  dimensions  smaller  than  0.01  µm, 
are subject to Brownian motion and their fall happens very 
slowly, but the particles that are larger than 10 µm fall quickly.
2. Dust and aerosols in the atmosphere (0.1-20 µm) serve as water 
vapour condensation centres and thus can be removed from the 
air.
3. Larger dust particles can collapse to form smaller size aerosols. 
This process is called dispersion. 
Since  the  spray  or  dust  particles  have  a  large  specific  surface 
area, they can sorb atmo spheric gases, chemicals, microorganisms 
and water vapour. Sorption process thereby determines the rather 
complex composition of aerosols. If the sorption results in a 
change of aerosols’ chemical composition, the process is called 
chemisorption, which occurs, for example, when sulfur, nitrogen 
oxides react with iron or aluminium oxide-containing aerosols.
Table 7.7.