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

Figure 7.23. 
The nature 
of dispersion and 
circulation of air masses 
and pollutants over 
urban areas 
The word ‘smog’ 
appeared about 70 years 
ago to describe a mixture 
of smoke and fog, which 
formed above London 
due to the temperature 
inversion processes. 
Later, this term was 
applied to certain 
adverse processes in the 
polluted atmosphere. 
Today, two types of smog 
are distinguished:
1.  the smog associated 
with the presence of 
smoke and soot, and 
a high SO
2
 content 
(‘London smog’); 
2.  the smog caused 
by a vehicle exhaust 
photochemical trans‑
formation reactions 
(‘Los Angeles smog’). 

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ENVIRONMENT, POLLUTION, DEVELOPMENT:  THE CASE OF UZBEKISTAN
descends slowly, a positive temperature gradient is formed in its 
volume and the mass of air that is subject to the inversion process, 
forms a shape similar to a huge lid covering the air mass below it. 
This type of inversion process may last several days, and there have 
been some cases of mass poisoning of population as a result of atmo-
sphere pollution directly related to the inversion phenomenon.
Heigh
t
Temperature
Heigh
t
Temperature
Inversion
Inversion layer
For the second type of smog, the prerequisite is a variety of 
photo chemical processes in the atmo sphere, so it is often called a 
photo chemical  smog. 
The main factor that determines formation of the photo chemical 
smog is air pollution with nitrogen oxides and hydrocarbons in 
the presence of intense ultraviolet radiation. The main source of 
nitrogen oxides and hydrocarbons in urban air is emissions from the 
vehicles.  When  these  emissions  enter  the  air,  a  series  of  different 
transformations can begin under the impact of intense ultraviolet 
radiation. These chains of transformations determine the rather 
characteristic process of changes in the content of pollutants in 
the photochemical smog, where the content changes of primary 
pollutants (NO, CO, hydrocarbons) and secondary pollutants (O
3
, 
aldehydes) can be observed over the day and night. The character 
of these changes allows one to follow the photochemical smog 
formation mechanism and to understand what processes determine 
the appearance of one or another substance in the air.
Obviously, the crucial role in these processes is played by 
hydrocarbons and their transformations. On the other hand,