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particles can cause allergic reactions and cause disease.
Aerosol retention in the human respiratory system depends on
the size distribution of particulate matter.
Pollen, dust of wood, flour and other organic substances can
be viewed as a special group of aerosols. Since these substances are
organic, their composition differs significantly from the composition
of the traditional dust, but among the potential effects on human
health the ability of these aerosols to cause allergies should be noted.
Aerosols and dust may adversely affect the plants, too. This
effect is characterized by the process of photosynthesis inhibition
and effects of toxic substances, as they desorb.
In the Uzbekistan major sources of dust are – loose dusty soils
and surfaces of salinized soils of Karakum, Kizilkum and Aralkum
(dry part of Aral Sea) deserts. Aeolian drift of sand and salt from the
dry bottom of Aral Sea yields 40-45 million tons/year, besides, the
main salt and dust erosion occurs within 300 km of coastal strand.
The amount of dust, which falls out on the soil in Juznoje Priaralje,
is ten times bigger than in the irrigated zone. The composition of
dust from Aral Sea includes sulfate salts up to 25-48%, chlorides –
18-30%, carbonates – 10-20%.
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ENVIRONMENT, POLLUTION, DEVELOPMENT: THE CASE OF UZBEKISTAN
The total capacity of anthropogenic sources of solid particle
emissions into the atmo sphere in the Republic is considerably lower
than of the natural ones and is evaluated at 1.311 millions of tons
per year. The share of solid particles in anthropogenic emissions
is not high and contributes 16% for industrial sources, and 2% for
mobile ones. The total amount of solid particles’ emissions in the
Uzbekistan from industry is much higher than from the transport.
The main sources of entry of the industrial dust are companies
of State Joint Stock Companies «Uzbekenergo», «Uzstrojmateriali»,
«Uzchlopkoprom». According to the statistical data for the period
from year 2000 to 2005, the total emissions of solid particles
increased from 88.993 thousand tons to 101.09 thousand tons, but in
year 2006 a notable decrease had been observed.
Index of total dust concentration in the atmo sphere is being
controlled in 18 industrial cities of Uzbekistan. Excessive dust
concentration is observed in large cities, in which lives approximately
41% of urban population. The level of air contamination with dust
is affected by high natural dustiness and industrial emissions. The
city dust characteristically contains soot, which is formed during
the combustion processes. The major mass of soot is being washed
away by precipitation. In exhaust gasses from automobiles, which
contribute in a certain way to dustiness of surface air, small particles
with diameter of 0.02-0.06 µm prevail.
Higher specific dust emissions are observed in cities, where
cement industry and coal-burning powerplants are mostly located.
Dust settling around industrial centres contains various mineral
compounds, metal oxides, silicates, soot, fluorides, arsenic oxides,
antimony and selenium. Among specific admixtures in dust contents
of large industrial cities are metals like cadmium, copper, lead,
nickel, zinc and manganese.
Since the aerosol effects on human, animal, plant and building
condition may be adverse, and according to mass, aerosols and
dusts must be considered the largest group of atmo spheric pollutant
compounds, it is important to limit their emission in the main areas
of aerosol formation, namely, industry and energy production.
To clean exhaust fumes from dust and aerosols several
approaches can be used:
1) The simplest method for air cleaning from dust is the
sedimentation of dust. Only coarser dust particles (>100 µm)
fall out sufficiently fast, and that limits the opportunities for
using this method;
2)
To clean the air from dust and aerosols, one can take the
advantage of the fact that the particle inertia is larger than
that of the gas molecules. This principle is used in cyclones
and dry centrifuges. In this case, the air to be purified is
introduced into a conical cylinder so as to create an air swirl
7. AIR POLLUTION
143
movement, where the heavier dust particles are thrown back
to the cylinder wall. Cyclones are the devices for continuous
operation.
3) Filtration of the air to be purified. Aerosols and dust can
be effectively removed by filtration of the air mixture to be
purified through suitable, such as asbestos, fibres, synthetic
material, glass fibre fabric. The filtration efficiency is
dependent on the filter material.
4) Scrubbers. In this case, a liquid is sprayed in the air to be
purified. The liquid gathers (and if accompanied by an
appropriate reagent also reacts with) the dust and aerosol
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