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

Figure 7.22. 
Global 
production of main ozon 
depleting substances

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7. AIR POLLUTION
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 7.6. 
 Urban air pollution problems
Air  quality  in  urban  areas  requires  particularly  careful  con-
si deration. This is determined not only by the fact that the urban 
environ ment is densely populated, but also because the cities have 
large  industrial  territories  and  intensive  traffic.  Thus,  the  charac-
teristic pollution can be observed in the urban environ ment, due to 
the high concentration of pollution sources and in many cases, the 
limited options for pollution dispersion.
The pollutant dispersion process in the urban areas is activated 
by the movement of air masses due to uneven warming of the Earth 
surface.  As  the  city  buildings  and  road  surfaces  intensely  absorb 
heat, in these territories the so-called «heat islands» are formed. This 
effect maintains the typical air mass circulation models in the cities 
that facilitate dispersion of pollutants. In this case, the contaminants 
(especially in the form of dust and aerosols) drop at a certain 
distance from the city limits creating a heightened pollution zone.
An important role in pollution dispersion is played by a vertical 
scattering process of air masses. Under normal circumstances, at the 
higher levels the air mass temperature decreases. However, there 
may be situations when the air temperature rises as the distance 
from the surface of the Earth increases. This state of the atmo sphere 
is called inversion, and it can be quite stable. In case of inversion the 
release of contaminants is hindered, and results in concentration of 
these substances in the places of discharge.
Inversion can be caused by two types of processes: first, with 
the advance of warm air to the air mass with a higher pressure 
and lower temperature or at night, as a result of the Earth surface 
losing heat. The first type of inversion processes take place as the 
air masses descend on areas with increased atmo spheric pressure. 
Under these conditions, air pressure and temperature of the air 
mass, which is subject to the inversion process and is located in the 
upper boundary, is higher than at the lower limit. If the air mass