Booklet No. 440
Ecology and Environment: EES - 7
II. Sources of Air Pollution
A. Natural sources
B. Man made sources
III. Consequences of Air Pollution
IV. Pollutants and Their Effects
A. Carbon monoxide
B. Green house gases
D. Sulphur dioxide
E. Nitrogen oxides and other gases
F. Particulate matter
G. Domestic air pollution
H. Air Pollution Control Devices
Air pollution is not an occurrence of the recent past or from the onset of industrialization
in the middle of 19th century. It is certainly as old as the first use of fire and the dust storms that
assuredly occurred on earth long before the advent of" Homo sapiens". Due to rapid
industrialization and agricultural revolution the level of air pollution has risen to unsafe limits.
This booklet describes the air pollution in detail.
Dr. K. T. Chandy, Agricultural &Environmental Education
Pollution is an act of making something physically impure and unclean. Air refers to the
invisible, tasteless mass of gases that surround the earth. The physical addition of material that
turn the air impure or unclean is called air pollution. The phenomenon of air pollution in man's
living environment is not a recent origin. High levels of smoke pollution in indoors was witnessed
at ancient times as our distant ancestors used to lit fires inside their houses. However, with
growing urbanization, industrial expansion, random deforestation threatened the ecological
balance. Since long in varying degrees the hazards and harmful effects of air pollution in urban
mass have been recognized.
Burning of low grade coal, which causes smoke and smog are used for domestic as well
as industrial purposes is by far the largest source of pollution. The exhausts of poorly
maintained automobiles are another source of pollution. Total emission in India has been
estimated to be about 23,412 million tonnes per annum. Out of this, 63.42% is contributed by
industrial sectors, 29.82% by domestic sector and 6.76% by automobiles. The 1984 Bhopal
tragedy is an example of air pollution caused by improper maintenance of industry.
By polluting air, man, the primary causal factor, has not only endangered himself but
also caused destruction to plants. The sources of air pollution, effects, and control measures are
described in the following pages.
II. Sources of Air Pollution
In air, pollutants may be in gaseous form or in particles of matter. Gases like carbon
dioxide, sulphur oxides, nitrogen oxides etc. which are emitted through combustion of fuel etc.
and particular matter which are very small in size but suspended or float in the air are the major
pollutants. The way these gases and particles of matter pollutes the atmosphere has been
discussed in the later pages. Mainly these pollutants may be through natural sources or man
made sources can be seen in Fig. 1
A. Natural Sources
Different natural sources of air pollution are described as follows.
1. Volcanic eruptions
Volcanoes emit hot lava and huge and dense cloud of dust laden with chemical fumes
rich in sulphur, methane and other gases are also emitted. The air borne dust is carried to long
distances as it is thrown up to a considerable height in the atmosphere where from the area of
its spread naturally becomes large.
2. Dust storms
Strong winds and storms naturally occur everywhere. At some places the amount of dust
carried by them is so much that the sun light is almost totally blocked. Huge amount of dust is
deposited on vegetation and house hold things besides causing damage to natural resources
and property. Poor visibility affects transport services and electric supply lines if telephonic wires
go out of order. Pollen and other microbial life reach to far off places and may cause allergy and
All the green plants are the sources of oxygen production and also consumption of
carbon-di-oxide. But they release organics which may react with atmospheric gases and
produce the common "blue haze" over the forests which can be seen from long distances. As
already mentioned, pollen of the plants may cause allergies and common allergy causing tree
species therefore should not be planted in social forestry and tree plantation programmes
around villages or city parks and road sides.
4. Forest Fires
Accidental fires in forests and savannahs and grasslands by natural processes of
lightning, friction between dried vegetation such as bamboos, etc. take place naturally. These
fires normally spread to large areas and throw out large quantities of semi-burnt ash, unburnt
hydrocarbons, carbon monoxide, nitrogen oxides, etc. which are the causes of air pollution.
Jhum or shifting cultivation practice in Meghalaya and Assam is to slash the forest, burn it and
raise agricultural crops on such areas which may create pollution on half-burning of such forest
5. Other natural sources
In other sources, decay of vegetable matter, animal wastes and dead bodies of animals
which is associated with release of gases like methane, ammonia and hydrogen sulphide, etc.
and foul odours into the air. Oceans are also the common source of aerosol emission of fine
particles of common salt. Fungal spores, bacteria and viruses reach to long distances by wind
action and spread viral fevers and several other diseases, some of which become epidemic.
B. Man made sources
Man made sources or anthropogenic sources are of many kinds. There is a large variety
of human activities by which air is subjected to pollution. These man-made sources can be
grouped into four which are given here in detail.
1. House hold activities
Kitchen is a domestic source of smoke and the collective smoke from all houses create a
yellowish cloud of smoke in the mornings and evenings over the village, town and city houses.
Combustion and incineration of waste matter give rise to fly ash, smoke and odours. The air
pollution caused by these agencies manifests itself most perceptibly during winter evenings
when the smoke, weighed down by fog, reduces visibility and causes irritation to the eyes.
2. Industrial emissions
Industrial pollution is the most important anthropogenic source. While converting the raw
materials into usable products there is a generation of considerable air pollution. Production of
metals like iron, copper or aluminium from their ores produce too much air pollution. While using
these basic materials in the manufacture of cars, planes or various other gadgets there is
pollution. These finished products like cars, trucks, etc. finally reach the roads and then pollute
the city air.
Combustions, which involve union of a substance with oxygen with emission of heat and
light, are the commonest source of air pollution. Usually combustion of organic substances
results in the formation of carbon dioxide, but in small quantities many harmful gases are also
produced such as carbon monoxide, nitrogen and sulphur oxides, fly ash, fluorides, metal
oxides and salts, acids, hydrocarbons, etc.
Around cement and asbestos industries highly hazardous air pollution problems are
3. Agricultural chemicals
In recent years, the use of agricultural chemicals like pesticides, fertilizers, rodenticides,
etc. has been increased. These chemical inputs no doubt increases the crop yield but at the
same time they pollute the air to a significant level. They have adverse effects on fish, wild life
and also on human beings. While applying to field by spraying, dusting, etc. they spread in the
air as dust and create harmful atmosphere. Large number of experimental studies have
indicated that DDT decreases the vitamin content.
4. Automobile emissions
Air pollution due to automobiles and other transport vehicles is now engaging the
attention in India. These automobiles and vehicles, either petro or diesel-driven are running in
densely populated areas with poorly ventilated streets. The exhaust gases from these vehicles
are emitted close to the ground, affecting human life. The smoke emission by a vehicle may be
due to the poor condition of the engine or the fuel injection system or poor general maintenance.
Air pollution caused by automobile exhausts causes the destruction of forests also.
III. Consequences of Air pollution
As world population increases, industrial growth expands and the emission of pollutants
will inevitably increase to a considerable extent. There is abundant evidence that high levels of
air pollutants may be generally harmful to human beings, animals and vegetation.
A. Effects on man
It has a direct effect on human health on inhalation. These effects may be classified into
acute and chronic effects. Air borne gasses, vapours, fumes, mists and dusts cause irritation to
the eyes and skin. This may seriously affect nose, throat, larynx and lungs. Some air pollutants
are reported to be carcinogenic.
B. Effects on animals
A survey report says appreciable number of animals become ill when they get exposed
to a polluted atmosphere. The vegetation near the copper smelters or phosphatic fertilizer plants
get contaminated with flourine. Cattles digest sufficient quantities of flourine and develop
flourosis. The animals first exhibit mottling and dulling of teeth, provide less milk and then
develop osteoflouritic bone lesions which cripple the animals.
Arsenic and cadmium oxide that are emitted while roasting non-ferrous metals may even
cause death to the animals. Lead compounds from automobile exhausts get deposited on
vegetation which is near the roads. The heavy metal poisoning symptoms are diarrhoea,
anaemia and stiffness.
C. Effects on vegetation
Air pollution has been found to affect plants in varying degrees. At the lowest levels, i.e.
below the "threshold", there is no effect, such as visible damage, chronic effects, genetic effects
or even gradual changes in the composition of plants. However, even at this level, air pollutants
could be stored in the plants and introduced into the food chain, affecting animals, which eat the
Plants take up air pollutants either directly through the interchange of gases with the
atmosphere or through the moisture taken up from the ~il. The ~il when exposed to air
pollutants get dissolved in soil moisture and these dissolved liquid pollutants are taken up by
plants. Gaseous pollutants enter the plants through stomatal openings. Solid particles of
pollutants settle on the plant surface and forms? waxy layer. Some solid pollutants slowly get
dissolved in water and enter into the plants through stomata from the surface. They can also
enter the food chain.
Plant damage can also be caused by the drifting action of chemicals which subsequently
blows to other areas and pollutes that area also. Pollution stress factors affects the plant
physiology by decreasing the activities of the plants. Details of pollutant effects on vegetation
can be seen from table 1. Besides, pollution affects aquatic life also.
Table 1: Pollutant Effects on Vegetation
Sl.No Pollutant Symptoms Maturity Part of leaf Injury Sustai
affected threshold ned
1 2 3 4 5 6 7
1 Sulphur Bleached Middle- Mesophyll 0.3 785 8 hrs
dioxide spots, aged most cells
2 Ozone Fleck, stipple, Oldest Palisade or 0.03 59 4 hrs
bleached most spongy
confier needle Youngest Paraenchyma
tips become least in leaves with
brown and sensitive no palisade
3 Peroxyac- Glazing, Youngest Spongy cells 0.01 50 6 hrs
etyl nitrate silvering or most
(PAN) bronzing on sensitive
4 Nitrogen Irregular, Middle- Mesophyll 2.5 4700 4 hrs
dioxide white or aged cells
lesions on sensitive
5 Hydrogen Tip and Youngest Epidermis 0.1 0.08 5
fluoride margin burn, leaves and mesopyll weeks
dwarfing, leaf most cells
6 Ethylene Sepal Young All 0.05 58 6 hrs
withering, leaf leaves
dropping and leaves do
failure of leaf not
to open recover
7 Chlorine Bleaching Mature Epidermis 0.10 290 2 hrs
between leaves and
veins, tip and most mesophyll
margin burn, sensitive cells
to that of
8 Ammonia “cooked” Mature Complete ~20 ~14,0 4 hrs
green leaves tissue 00
9 Hydrogen Acid-type Oldest Epidermis ~5- ~11,2 2 hrs
chloride necrotic leaves and 10 00
lesions, tip most mesophyll
burn on fir sensitive cells
10 Mercury Chlorosis Oldest Epidermis <1 <820 1-2
and leaves and 0 days
abscission; most mesophyll
brown sensitive cells
11 Hydrogen Basal and Youngest - 20 28,00 5 hrs
sulphide marginal leaves 0
12 2,4- Scalloped Youngest Epidermis <1 <9.05 2 hrs
Dichloro- margins, leaves 0
phenoxyace swollen most
-tic acis (2- stems, yellow affected
4D) green mottling
13 Sulphuric Necrotic spots All - - - -
acid on upper
D. Threat of acid rain
The phenomenon of acid rains is fast becoming a grave global ecological problem
threatening farms, forests, aquatic life and human health. With the rise of industry, more power
plants and more vehicles, gases like sulphur-di-oxide, hydrogen sulphide and nitrogen oxides
are released into the atmosphere at a greater rate than before. Large quantities of these gases
combine with water vapour to produce strong acids. A strong acid rain affects the foliage of
trees and plants and also has an adverse effect on their growth activities. When acid rains fall
on a lake or stream, the bottom of the lakes and streams becomes acidified and eventually
harm the fish and also the fertility of soil. As a result it drastically reduces the fish population and
Besides, water and fish from these polluted lakes are harmful to human health. The
cycle of acid rains can be seen in the fig 2.
As water becomes acidified, the amount of aluminium in it starts to increase rapidly. At
the same time, phosphates get attached themselves to the aluminium and become less avail-
able to plants. As water gets more acid still, other metals like, cadmium, zinc, lead and mercury
also become increasingly soluble and affects living beings.
Soils are normally much better resistors of acid rains. But, unavailability of nutrients and
accumulation of heavy metals are the possibilities which may harm the lives of animals and
IV. Pollutants and their Effects
There are different types of pollutants of which only the important ones are descnbed
A. Carbon monoxide
Carbon monoxide gas is formed by incomplete combustion of fossil fuel like coal and
petroleum or other organic matter. Automobiles are the commonest source of carbon monoxide
pollution in cities. Other common sources are oil refineries, metallurgical operations and other
internal combustion engines.
It is a major pollutant for man and other animals as it combines with blood hemoglobin
much faster than oxygen. It combines with hemoglobin more than 200 times faster than oxygen
does. So, an air containing carbon monoxide (CO) when inhaled, will not be so effective in
respiration or oxygenating the hemoglobin as clean air. Therefore, in rooms with burning coal,
CO causes suffocation though oxygen content is not less. It is estimated that this gas accounts
for about half of the total air pollutants added to atmosphere. Vegetation is regarded as natural
sink for CO pollution. Besides vegetation, soil and ocean also act as natural sinks and promote
In blood stream, CO interferes with the function of hemoglobin by forming CO-Hb and
reduces the physical endurance of a person and produces adverse effects on the cardio-
B. Greenhouse gases
Several of the gases naturally present in earth's atmosphere have the ability to absorb
radiating out infrared heat waves and reflecting them back to the surface of the earth. This
causes a wam1ing effect. In a greenhouse made of glass top, the sunlight enters the
greenhouse and glass top and the reflected out heat is held up by the glass walls and the glass
roof and the greenhouse warm up as shown in Fig 3.
Likewise, solar radiation in the form of electromagnetic waves pass through the atmosphere and
reach earth's surface. Some radiations are reflected back into the atmosphere. This heat is held
up by many gases that are present in the atmosphere. But the increase of greenhouse gases
like carbon dioxide, methane, chIoro-fluro-carbons, nitrous oxides results in global warming. In
fact some warming up from 0.3-0.7 °C has already taken place during the last one century.
Greenhouse effect at its natural level is very essential for life to exist on this earth, but its
increase, as is actually taking place in recent decades, is feared to cause global climatic
changes of a highly destructive type. Main gases that are creating the greenhouse effect are
1. Carbon dioxide (CO2)
Carbon dioxide is a natural resource and is present in the atmosphere to the level of
0.03%. It has "the green house effect" or warming up of air. This gas and some others,
particularly the water vapour in the atmosphere have the ability to allow solar radiations to pass
through and reach ground surface but 011 radiation the out going heat waves or infra red
radiation are held up or tapped by them.
Carbon dioxide is a major gas whose concentration is rising and is posing the threat.
The carbon dioxide content has risen by 25% and it may double itself by the year 2050. It has
an adverse effect on human health because it may lead to oxygen deficiency besides the green
2. Chloroflourocarbons (CFCs)
Chloroflourocarbons are chemicals which are used in many kinds of industries.
Important ones are CFCl or CFCl3 and CFCl2 or CF2 Cl2 (trade name "Freon"), CCl4 (carbon
tetrachloride) and CF 4 and occur in aerosol and non-aerosol form. Aerosol form is suspected to
damage the ozone layer. Ozone layer is extremely essential as it cuts down the ultraviolet rays
reaching the earth. If CFCs increase in the atmosphere, the ozone layer will slowly get depleted
and harmful ultraviolet rays reaches the earth and these are dangerous to living beings.
Methane (CH4) is another greenhouse gas and biological processes like enteric
fermentation in cattle, sheep and other animals, anaerobic situations in wetlands and rice fields
and burning of biomass and fossil fuels by man are the main sources of methane. Methane gas
increases stratospheric water vapour on oxidation. The rise in water vapour is really more
important source of greenhouse effect than the direct effect of methane gas. Among the man-
made sources highest contribution is by cattle or ruminants releasing 120 ton gms/year (1 tg =
1012 g or 106 tones), rice fields 95 tg/year and biomass burning 25 tg/year. Apart from these,
automobiles, coal mining, natural gas flamings increases the methane gas content in the
atmosphere. It increases the temperature and causes global warming.
4. Nitrous oxide
Nitrous oxide (N20) emitted from the burning of fossil fuel is another greenhouse gas. Its
content is also reported to be rising allover the world. Current rates of increase is about 0.2-
0.3% per year. Besides the emissions of burning of fossil fuels, it also reaches the atmosphere
from the breakdown of manures and fertilizers. On reaching the upper layers of the atmosphere
it slowly reacts with oxygen leading to global warming.
Besides, carbon dioxide, chloroflourocarbons, methane and nitrous oxides, other traces
of gaseous forms of sulphur, nitrogen, flourine, bromine, iodine, etc. also have the impact on the
overall global warming but the impact is small when compared to major sources that are already
Greenhouse effect is a slow and imperceptible process and its effect is long lasting.
Warming up would lead to significant changes in the forest species and change in natural
growing condition may require modification in forest management Greenhouse effect on crop
production varies in different regions. In the thermal region even 2°C rise in temperature is
harmful. Increase in temperature increases evapo-transpiration. With warm temperature, pest
infestation will increase, and this reduces the crop productivity. So, heat, drought and pest
tolerant varieties should be evolved. Cycling of the nutrient elements may be accelerated and
this may upset the fertility status of soil. Despite warm temperature and reduced moisture,
decomposition of organic matter is retarded. It will lead to greater use of chemical fertilizer.
Thus, greenhouse effects will lead to alteration in cropping patterns, plant breeding for evolving
suitable varieties to grow better, in the predicted climate and to resist pests.
Greenhouse gases are certainly going to alter the temperature regimes and therefore
the hydrologic cycle. It will also affect the infiltration and storage capacity in soil pool. All these
changes affect the human health. Several diseases break out particularly skin and lung
diseases. Maximum temperature goes up and minimum temperature will go down.
Ozone gas is found in traces in the air near the ground surface and in concentrated thick
layer at varying heights in the troposphere from 16 km about 40 km at different latitudes. It is a
phytotoxic air pollutant gas of significant importance. Several experiment showed that it is
injurious to plants after a certain level. But, in the stratosphere, ozone layer forms a shield
against the harmful ultraviolet radiation coming from sun. The greenhouse gases like carbon
dioxide, methane, CFCs, etc. are slowly depleting this ozone layer reducing the ozone zone,
thus they are creating more harmful situations for safe living of the human beings. It increases
the incidence of skin cancers, cortical cataracts, suppression of immune systems in man and
decrease the yield of many crops and reduce oceanic phytoplantation populations.
Nitrous oxide present in the atmosphere destroys chlorine monoxide and thereby checks
ozone depletion. Ozonator is a machine to produce ozone and it is solar powered. It can be
taken up by balloons to plug the ozone holes.
D. Sulphur dioxide
Sulphur dioxide (SO2 is emitted into the atmosphere and next to carbon monoxide, it is
the contaminant which is most abundantly present. With growing industrializaiton the level of
S02 concentration is rising day by day. The principal man made sources are thermal power
plants metallurgical operations, refinaries and the like which burn huge quantities of fossil fuel.
Coal and crude petroleum contain some quantity of sulphur and on burning the fuel it gets
converted into SO2 reaches the atmosphere. This may form a smog which is injurious to health.
One more important role of SO2 pollution is its reaction with atmospheric moisture and
formation of sulpherous and sulphuric acids which come down with rain water. When the acid
content becomes high and pH falls down to 5.4 or even up to 2.5 we call it "acid rain" which
damages crops, forests, aquatic ecosystems, corrodes the buildings, affects the drinking water
storage sources and upsets the soil biological processes. Acid rain problems have been
frequently experienced in different parts of the world Industries are required to install SO2
trapping mechanisms from the chimney smoke.
E. Nitrogen oxides and other gases
Nitrogen is the most abundant gas in air accounting for 78% but it is inert, does not
readily take part in biological processes, unless it is fixed by various processes of nitrogen
fixation. Man made source of nitrogen oxide are primary and are through burning of fossil fuel.
Besides this, industries, diesel and petroleum burnt in motor vehicles and railways produce
nitrogen dioxide. High concentration of nitric oxide is lethal as it can combine with hemoglobin
much faster than oxygen. It causes gum inflammation, internal bleeding, oxygen deficiency and
possibly pneumonia and lung cancer. NO2 injury in plants is by acid formation through photo
oxidation. The reduction in the rate of photosynthesis is also possible.
Peroxyacetyl nitrate is a secondary pollutant forming smog by the action of light on
hydrocarbons and nitrogen oxides in air. It may enter the plants through stomata and reduces
photosynthesis through injury to chloroplast inhibition of electron transport, and interference with
enzyme systems connected with photosynthesis.
Smog has been found to be the cause of death of human beings in large numbers.
Smog is also responsible fl)r causing or aggravating chronic diseases like bronchitis and
asthma. General discomforts like eye initiation and unpleasant odours are most common. Smog
is not necessarily the combination of smoke and fog as earlier thought of. It is the haze or
merely condition of atmosphere near ground level which reduces the visibility. It is most abudant
in a traffic jam during rush hours in big cities and industrial areas.
Hydrocarbons are also most common in heavy traffic regions and at times in the cities
where automobile engines release this gas. This causes injury to plants distortion of foliage,
excessive disturbance in growth, behaviour, leaf chlorosis, senescence, and abscission of
Adverse effects of flouride gas are also noticed which may cause necrosis, etching,
chlorosis and discoloration of plant parts.
F. Particulate matter
In the air, there are several very minute particles that keep floating all the times, which
constitute this particulate matter. Even the clean air contains some particulate matter like pollen
grains, fungal spores, bacteria, viruses, fine carbon particles, soil dust, coal dust, cement dust,
absestos dust, etc.
Aerosol is the commonest word used to denote any kind of small particles found floating
in the air. Usually particle size below on micron in diameter is an aerosol and larger than
aerosols, i.e. above one micron, they are called as dust for solids, and mist for liquids. Smokes
and fumes are the examples for aerosols.
The particulate matter present in the air has many effects. Some are pathogenic and
infect plants, animals and man through wind dispersal. It alters the heat balance of the
atmosphere at local and regional levels. They affect visibility. At heavy traffic points it not only
reduces the visibility but causes burning sensation of the eye and may initiate coughing.
Industrial, mining and metallurgical operations produce lot of metallic dusts of copper,
iron, zinc, steel, lead and aluminium. Among non-metallics, industrially produced dusts are of
cement, ceramics, absestos, etc. These particles reach the air during blasting, loading and
unloading, drilling, crush- ing, grinding and drying of slurry, etc.
In metallic pollutants, arsenic contamination leads to stunted growth, death of fine rots
and is also harmful' to living beings. Cadmium aerosol settle with rain on plants and through
food chain reach animal and man. It causes several problems in plants such as chlorosis, foliar
injury, root injury, etc. In man it causes cardiovascular problems and hyper tension. Copper is
another important pollutant which wipes out the vegetation in course of time near copper and
nickel smelters. Lead reaches to urban environment from motor vehicles and is poisonous to
Cement dust is a non-metallic dust which is produced in huge quantities from house
buildings, road and bridge construction. It is an oxide of calcium and silica which when it
becomes wet forms hard calcium silicate. Very fine dust of cement pass out into the air and are
quite heavy particles which settle down on plants, house buildings and bodies of the persons. It
also finds its way into the lungs through inhaling air. Cement dust on leaf surface forms a thin
but hard crust and seals the stomatal surface.
Asbestos dust is also reported to cause lung infections particularly asbestos's cancer of
the lungs. Therefore, utmost precaution and education of labour class handling asbestos are
G. Domestic air pollution
Pollution control is equally important in indoors, i.e. within our houses and offices. The
commonest and most dangerous pollutant is cigarette and other tobacco smokes. Next is
kitchen smoke particularly in Indian villages where it arises due to incomplete combustion of
wood and cow-dung cakes which , are commonly used as fuel.
Cigarette smoking in public places, like offices, aeroplanes, trains, buses, cinema
houses, etc. affects the non-smokers also. Kitchen smoke is another serious air pollutant that is
most common in all in ventilated houses. Proper provision for the escape of smoke is essential
in the kitchens, otherwise it leads to eye irritation, throat irritation, lung infection etc.
Commonest indoor pollution gases are carbon monoxide and carbon dioxide among
which the former is formed due to incomplete combustion of wood, coal or other fuel and the
latter reaches harmful levels in closed or ill ventilated kitchens.
So, in order to reduce indoor air pollution, banning of tobacco smoking and cross
ventilation in indoors are the two important aspects that should be taken into consideration.
A gist of all the pollutants and their effects can be seen in table 2.
Table 2: Selected atmospheric pollutions
Sl.No Pollutant Principal human Effects Remarks
1 Carbon Fuel No direct effect on Normal constituent
dioxide combustion for people, over time, of atmosphere.
heating, may lead to increase Essential to plant life
transport, in earth’s
2 Carbon Incomplete fuel Deprives oxygen, Contribution of
monoxide combustion (as people with cardio- natural sources,
in motor respiratory diseases small smoking, more
vehicles) more sensitive significant for human
than exposure to
3 Sulphur Burning of Combined with “” “”
dioxide Sulphur smoke increases risk
containing fuels and effects of
like coal and oil respiratory diseases.
irritation of throat and
eyes, combines with
vapour to produce
acid rains. Reduces
crop yields. Lead to
acidification of lakes
and soils, corrodes
4 Suspended Smoke from Possible toxic effects Chemically a most
particulate domestic depend specific diverse group of
matter industrial and composition. substances. Natural
vehicular Aggravates effects of sources include dust
sources Sulphur dioxide. storm, volcanic
Reduce sunlight and eruptions and sea
visibility. Increases spray
5 Oxides of Fuel Possible increase in Nitrogen oxide and
nitrogen combustion in acute respiratory nitrogen dioxide are
motor vehicles infections and the two components
and furnaces, bronchitis morbidity
forest fires in children. Produces
brown haze in city
air. Causes corrosion
6 Volatile Partial React with other “ “ “: “ “ “
Hydrocarbons combustion of pollutants to produce
carbonaceous eye irritants (acrolien
fuels, industrial aldehydes). Ethylene
processes, is harmful. Aerosol
dispersal of particles reduces
solid wastes visibility. May
7 Oxidants & Emissions from Cause eye irritation & Mainly derivative
ozone motor vehicles. impaired pulmonary products of
Photochemicals function. Corrode atmospheric
reaction of materials and reduce reactions between
nitrogen oxides visibility. other pollutants.
8 And reduce Pollutants Ozone is one of the Ozone is a natural
most damaging and essential
pollutants for plants constituent of the
V. Air Pollution Control Devices
Besides taking natural control measures to reduce pollutant gases to a minimum, certain
pollution control devices can be used in industries. Some of them are described here.
A. Bag filter
Particulate matter can be filtered if the fumes containing them are forced to pass through
a filtering device. The particles are held while the gases pass out of the filter. Typical industrial
filters are bag type and are called bag filters. Huge cylindrical bags of necessary pore size are
used through which the dust laden fumes are passed through under certain pressure. Peri
odically, the bag contents are shaken out in dust collection containers and suitably dispensed.
B. Cyclone collector
Another device is to whirl the dust containing fumes at great speed so that the
particulate matter with heavier density is thrown out or separated and collected. Such a device
is called as cyclone collector which can be seen in fig 4.
In this, the smoke is fed in a conical cylinder placed vertically. Inside the cone is a device to
whirl the fumes at desired speed. The solids being heavier are spun out and collected through
the dust outlet while the free gas goes out from the top. This is quite an effective device in small
C. Electrostatic precipitator
Particles in smoke emitted out of chimneys are of different sizes. While large particles
easily settle down due to gravity, the smaller ones float for long in the air and reach long
distances, They are extremely small sized and electrically charged particles and these small
dust particles are separated out of the smoke using a device of attracting and settling the
charged dust on an oppositely charged electrical device. This is the basic method on which
different models of electrostatic precipitators are built, It consists of a thick cylinder with an inlet
and an exit, In the cylinder, a discharge electrode is inserted from the top to the bottom and
connected to a high voltage cable. The dust laden fumes produced in furnaces and kilns are
passed into the ESP (electrostatic precipitator) from the gas entrance inlet and on coming under
the influence of oppositely charged electrode, the dust particles settle on the charge surface.
The accumulated dust gradually fall down and from the outlet it comes out of the cylinder. The
clean, dust free smoke, rises through the cylinder and gets expelled out of the exit (Fig. 5).
Depending on the volume of fumes to be handled, different capacities are built They are
expensive and power consuming but taking the hazards 9f particulate matter pollution into
consideration such a cost must be incurred while setting up heavy industries and super thermal
D. Scrubber or pray collector
To remove the toxic substances before the emission of smoke, this spray collector is
useful. Water is one of the best solvents and it is used to dissolve as much of the toxic part of
the gas as possible by bringing the fumes in intimate contact of spraying water.
There is a cylindrical spray tower in which the factory fume is pumped from an inlet on
the lower side wall. It comes in intimate contact with showered water. Alternatively the gases
are bubbled through the solvent liquid. For example, factories producing fumes containing
ammonia become free of this gas when either passed through a scrubber or bubbled through
E. Activated carbon absorber
Activated carbon powder has a large surface area and due to electrical charge on their
surface they absorb many of the pollutants when the gaseous emissions are passed through a
column of such an adsorb ant. This is also quite an effective method of pollution control in
certain cases. If the adsorbed substances are useful, then they can be recovered from the
activated carton for use while the carton can be re-activated and reused.
Different chemicals for different types of pollutants can be used to react with that or to
precipitate them out. Infact by chemical methods, the pollutants can be converted into
economically useful products.
For example, around 85-90% sulphur dioxide removal in power plants has been
successfully achieved by wet adsorption technique using limestone of dolomite or using oxide of
manganese. Even dry adsorption using activated carbon ensures 90% efficiency in sulphur
dioxide removal. The adsorbed sulphur dioxide is used in preparation of sulphuric acid as a by
product. For hydrogen flouride pollution control scrubbers are recommended. The device can be
99% effective. Nitrogen oxides are also partially removed by water sprays.
India with a face-lift in industrial development in the present times is facing problems in
pollution control. Concerted effort by Government to control emission through per- suasion and
legislation certainly improves air quality. Methods include the use of cleaner fuels, the
achievement of more complete combustion and installation of filters or precipitators to recycle
industrial wastes. The heights of the chimneys are so chosen to ensure that the local air quality
standards are met.
The environment management agencies have to monitor the air quality from time to
time. The choice of sampling methods be based on the availability of monetary and personnel
facilities. For long range pollution control from large emission sources engineering control
methods are a must, but for large number of small emission sources and for marginal emission
from large sources, biological methods or abatement methods could be most suitable and
economical. A number of benefits can be obtained from urban plantations for environmental
improvement and air pollution abatement.