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

Table. 
Main substances that affect the ozone layer
Substance
Usage
Lifetime in the 
atmosphere, years
Freons, CFC – 11 CFCl
3
In aerosols, refrigerant
55
CFC – 12 CF
2
Cl
2
In aerosols, solvent
116
CFC – 22 CHFCl
2
Solvent
400
Chloroform, CHCl
3
Solvent, reagent
0.7
Carbon tetrachloride, CCl
4
Solvent, in firefighting
4.7
Nitrogen oxides, NO
x
In industry, energy
A couple of days
Methane, CH
4
In agriculture, industry
10.5
The ozone concentration 
in the atmosphere is 
expressed in gas concen‑
tration units of measure 
(mg/m
3
, µg/m
3
) or in a 
special unit of measure 
called the Dobson unit 
(DU) in honour of Gordon 
Miller Bourne Dobson, 
who was one of the first 
scientists studying the 
atmospheric ozone. One 
Dobson unit is a 0.01 mm 
thick ozone layer under 
standard temperature and 
atmospheric pressure.
Figure 5.4. 
Ozone 
molecule formation 
induced by UV radiation

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5. GLOBAL ENVIRONMENTAL PROBLEMS
 79
Halogenated hydrocarbon molecules are composed of carbon, 
hydrogen and halogen (F, Cl, Br, I) atoms. Those halogenated 
hydrocarbons whose molecules contain one or two carbon atoms and 
have their remaining hydrogen atoms replaced by fluorine or chlorine 
atoms are called freons. Considering the wide range of industrial 
use of these substances, their production in industrial quantities 
began in the 30s of the 20
th
 century. Initially freons were used as a 
replacement for such hazardous and toxic gases as ammonia (NH
3
) 
and sulphur dioxide (SO
2
) in refrigerators. Since freons had low 
toxicity and were non-combustible, they were found useful in a wide 
range of other applications as well. At the end of the 1980s, the total 
production amount of freons reached 1.2 million tons per year.
Freons are emitted into the environ ment as a result of specific 
features of technological processes (e.g., refrigeration systems), after 
use of products (e.g., aerosols) and in technological processes (e.g., 
microchip cleaning). The lifetime of freons in the atmo sphere is 
from 29 to 500 years. After entering the stratosphere, freons interact 
with  UV  radiation,  releasing  chlorine  or  fluorine  atoms  that  can 
subsequently become involved in ozone degradation reactions.
The reduction of the ozone concentration (the ozone layer 
depletion) was observed for the first time over the Antarctic, where 
natural processes initiate an especially intensive breakdown of ozone 
molecules (Figure 5.5). At the beginning of the 1970s, the size of the 
Antarctic ozone hole was a few million square kilometres, while now 
it exceeds 25 million square kilometres.
<150  175  200  225  250  275 300  325  350  375  400  425  450  475  >500
Figure 5.5. 
Profile of 
the ozone hole over 
the Antarctic (ozone 
concentration in 
Dobson units)

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80 
ENVIRONMENT, POLLUTION, DEVELOPMENT:  THE CASE OF UZBEKISTAN
The decrease in the ozone concentration in the stratosphere 
increases the intensity of UV radiation reaching the Earth’s surface. 
UV  radiation  is  divided  into  three  radiation  ranges  with  different 
wavelengths  according  to  its  biological  effect:  UV-C  (wavelength 
λ <290 nm); UV-B λ= 290-320 nm) and UV-A (λ= 320-400 nm). 
UV-A and UV-B radiation reaches the Earth’s surface. Window glass, 
for example, absorbs most of this radiation. UV-C and a significant