Air Pollution Unit-I & VIII

1. Air PollutionUnit- I & VIII

2. Syllabus
Air Quality Management
Air pollution fundamentals, Air quality
management, control technologies.

3. Air Pollution
• Definition:- Air pollution is define as
“Excessive concentration of foreign matter in air, which
adversely affects the well being of individuals or causes damage
to the property”.

4. Composition of Air

5. Ambient Air Quality Standards
Pollutant
Time Weighted
Average
Concentration in Ambient Air
Industrial Area
Residential, Rural and
other
Sensitive Area
Sulphur Dioxide (SO2)
Annual
24 hours
80 µg/m3
120 µg/m3
60 µg/m3
80 µg/m3
15 µg/m3
30 µg/m3
Oxides of Nitrogen
(NO2)
Annual
24 hours
80 µg/m3
120 µg/m3
60 µg/m3
80 µg/m3
15 µg/m3
30 µg/m3
Suspended Particulate
Matter (SPM)
Annual
24 hours
360 µg/m3
500 µg/m3
140 µg/m3
200 µg/m3
70 µg/m3
100 µg/m3
Respirable **
Particulate Matter
(RPM)
Annual
24 hours
120 µg/m3
150 µg/m3
60 µg/m3
100 µg/m3
50 µg/m3
75 µg/m3
Lead (pb)
Annual
24 hours
1.0 µg/m3
1.5 µg/m3
0.75 µg/m3
1.00 µg/m3
0.50 µg/m3
0.75 µg/m3
Carbon
Monoxide(CO)
8 hours
1 hour
5.0 µg/m3
10.0 µg/m3
2.0 µg/m3
4.0 µg/m3
1.0 µg/m3
2.0 µg/m3
* Ministry of Environment and Forests, Government of India notification
** Particle size less than 10 µm

6. Major Sources of Air Pollution

7. Major Sources of Air Pollution
• Natural Sources:- The natural sources of air pollution are volcanic
eruptions, releasing of poisonous gases like SO2 ( Sulfur dioxide),
Hydrogen sulphide (H2S), Carbon Monoxide(CO), Forest fires,
natural organic and inorganic decays, Pollen grains, wind blown
dust, among them pollen grain are important because it causes
allergic reactions in individuals.

8. Major Sources of Air Pollution

9. Anthropogenic Sources
• Rapid Industrialization:- The Industries such as pulp and paper,
chemical, metallurgical plants, refineries are responsible for air
pollution, the most common pollutants are CO2, SO2, CO, NO, H2S
etc..
• Transportation:- Automobile exhausts release smoke. The smoke is
a result of incomplete combustion of carbonaceous matter. The
common pollutants are CO(Carbon Monoxide), CO2, and
Hydrocarbons.
Rapid Industrialization Transportation

10. • Burning of Fossil fuels and fires:- The conventional sources of
energy are wood, coal, and fossil fuels. The byproducts of fossil
fuels is nothing but poisonous gases such as CO, CH4 (methane),
SO2, and NOX.
• Deforestation:- The balance of O2 and CO2 is maintained in the
nature by the vegetation. The deforestation by man for his own
needs has disturbed the balance of CO2 and O2, Concentration.
Burning of Fossil fuels and fires Deforestation

11. • Increase in Population:- an increase in population leads to global
warming and emission of green house gases. It also contributes to
losses in forest cover and loss of wild life.
• Agriculture activities:- Various pesticides and insecticides are used
for agricultural purposes. Thus they cause air pollution.
• Radioactive fallout:- Nuclear reaction, nuclear weapon testing
contributes towards Nuclear pollution. Nuclear Pollutants are very
harmful to man, animals and vegetations.

12. Anthropogenic sources
Increase in Population
Agriculture activities
Radioactive fallout

13. Classification of Air Pollutants
• Air pollutants are broadly classified as
• (a) According to origin
• (b) According to chemical composition
• (c) According to State of matter.

14. According to Origin
• Air Pollutants can be classified as
• (a) Primary Pollutants
• (b) Secondary Pollutants
• Primary Pollutants:- Primary pollutants are those which are
directly emitted from identifiable source
• These pollutants are emitted directly to the atmosphere.

15. • e.g.
(a) Particulate matter
(b) Oxides of Sulphur
(c) Oxides of Nitrogen
(d) Carbon Monoxide
(e) Radioactive Compounds

16. Particulate Matter

17. Oxides of Sulphur

18. Oxides of Nitrogen

19. Carbon Monoxide

20. Radioactive Compounds

21. • Secondary Air Pollutants:- Secondary air pollutants are those
which are produced in the air by the reaction of two or more
primary pollutants.
• e.g.
• Ozone
• Formaldehyde
• Photochemical smog
• Peroxy acetyl nitrate (PAN)

22. Secondary Air Pollutants
Ozone
Formaldehyde

23. Secondary Air Pollutants
Photochemical smog

24. Secondary Air Pollutants
Peroxy acetyl nitrate (PAN)

25. According to Chemical Composition
All the air pollutants are classified as
(a) Organic Pollutants
(b) In Organic Pollutants
(a) Organic Pollutants:- Organic Pollutants contain carbon and
hydrogen.
e.g.
• Hydro Carbon
• Aldehyde and Ketones
• Alcohols
• Organic Sulphur compounds

26. Inorganic Pollutants:- Inorganic compounds mainly includes
(a) Carbon monoxide (CO)
(b) Carbon dioxide (CO2)
(c)Carbonates
(d) Oxides of sulphur, nitrogen
(e) Ozone

27. Organic Pollutants
Hydro Carbon

28. Inorganic Pollutants
Carbon dioxide (CO2)

29. According to State of Matter
Air pollutants according to state of matter are classified as
(a) Natural Contaminants
(b) Particulate Matter
(c) Gases and Vapours

30. Natural Contaminants
• The air contaminants which are produced from natural sources are
called natural contaminants
• Eg. Pollen grains are emitted from weeds, grasses and trees
• This pollen grains are irritating to some individuals
• Size of pollen grains = 10 to 50 (µ)
Pollen Grains

31. Particulate matter
These may be liquid or solid. The
particulate matter are identified as
aggregates which are larger than
0.002 µ but smaller than 500 µ
Dust (1 To 10,000 µ) : Small solid
particles resulting from break up of
large masses through processes such
as crushing, grinding or blasting.
Smoke ( 0.5 To 1 µ) Consist of finely
divided solid particles produced by
incomplete combustion of organic
particles such as coal, wood, or
tobacco.

32. • Mist:- These are liquid particles formed by condensation of vapor
• Fog (1 to 40 µ ):- High concentration of mist is called as fog. It is
dispersion of liquid particles in air.
• Fumes ( 0.03 to 0.3 µ ):- Fine solid particles formed by the
condensation of vapors of solid material. The fumes are generally
emit from melting operations.
• Ash ( 1 to 1000 µ ):- fine, noncombustible particles are known as
fly ash.
• Spray (10 to 1000 µ):- Liquid particles formed by automation

33. Particulate Matter
Mist Fog
Smoke Ash

34. Gases And Vapors
• Carbon Monoxide:- (CO) This is an odorless, tasteless and colorless
gas formed due to incomplete combustion of carbonaceous matter.
The sources of carbon monoxide are motor vehicles, burning of
fossil fuel and industrial processes.
• Oxides of Sulphur:- They Include 4 different gaseous compounds
such as Sulfur monoxide ( SO), Sulfur dioxide ( SO2), Sulphur
trioxide ( SO3) and sulphur tetra oxide (SO4).
• It is a major air pollutant gas produced by the combustion of fuels like
coal. The main source of electricity production is by burning of fossil fuels
in India and the whole world. The sulphur content of the coal varies from
1 to 4% and fortunately the Indian coal is low in sulphur content. SO is
also produced in the metallurgical operations.

35. Gases And Vapors
Carbon Monoxide

36. Oxides of Nitrogen
Oxides of Nitrogen
• Oxides of nitrogen are produced either in the production of
nitric acid or in the automobile exhausts and as the effluent of
power plants.
• Out of the seven oxides of Nitrogen (N2O, NO, NO2, NO3, N2O)
• only nitric oxide and nitrogen dioxide are classified as the
main pollutants.
• All the oxides of nitrogen are collectively known as NOX.

37. Hydrocarbon
• Organic compounds containing only carbon and hydrogen are
classified as Hydrocarbons.
• They are of 2 types.
• (a) Aliphatic hydrocarbon
• (b) Aromatic hydrocarbon
• Hydrocarbon present in the atmosphere in the atmosphere from
both natural and man made sources.
• The major sources of hydrocarbon is burning of gasoline and
industrial processes.

38. Aliphatic hydrocarbon

39. Aromatic Hydrocarbon

40. Other Gases
• Hydrogen Sulphide: Hydrogen Suphide is an obnoxious (bad smelling) gas. It
is produced mainly by the anaerobic (in absence of air) decomposition of
organic matter. Other air polluting sulfur compounds are methyl mercaptan
(CH3 SH) and dimethyle Sulphide (CH3 S CH ) etc..
• Hydrogen fluoride: It is an important pollutant even in very low
concentrations. It is produced in the manufacturing of phosphate fertilizers.
• Chlorine and hydrogen chloride: It is mixed in the air either from the
leakages from water treatment plants or other industries where it is produced
or used. Hydrogen chloride is also evolved in various industrial chemical
processes. The main effect of chlorine is respiratory irritation which may be
fatal.
• Ozone: It is a desirable gas in the upper layers of atmosphere as it absorbs the
UV radiation of sunlight. But near the earth surface it is a poisonous gas. It
makes poisonous chemicals by photochemical reactions.

41. Other Gases
• Aldehydes: They are produced by the incomplete oxidation of motor fuels
and lubricating oil. They may also be formed because of photochemical
reactions. Formaldehydes are irritating to the eyes.

42. Other Gases
Hydrogen Sulphide Hydrogen fluoride
Hydrogen Chloride
Ozone

43. Classification Based On Position
• Another way of classification of air pollutants is the source being
stationary or mobile.
• This way they can be classified as:-
• (i) Point source (large stationary source as power plants)
• (ii) Area source (small stationary sources like residential heating)
• (iii) Mobile source (line source like highway vehicles or area
source like Aircraft at airports)

44. Point Source

45. Area Source

46. Mobile Source

47. Air Pollutants And Their Major Sources.

48. Effects of Some Common Air Pollutants
Particulate Matter
• Effects on human:-
• The pollutants of size less than 1 µ causes lung damage
• Asbestos fibers causes cancer
• Lead from automobile exhaust affects brain
• It causes several respiratory diseases
• Silica , arsenic, dust causes cancer

49. Effects of Air Pollution on Humans

50. Effects of Air Pollution on Humans

51. Effects on Plants
• Deposition of particulate matter containing toxic metals affects the
growth of plants
• The particulate matter after deposition on plant leaves block
stomata opening of plants and reduce plant growth.
• The particulate matter with acid rain, reduces pH of the soil which
makes the infertile.

52. Effects on Plants

53. • Effect on Material
• The particulate matter causes damage to building
• The corrosion is enhanced
• It causes cracks and fading of pointed surface
• Particulates accumulate on the soil and reduces fertility of soil.

54. Effect on Material

55. Carbon Monoxide
• Effects on humans
• The high concentration of CO can cause death
• The combination of CO and hemoglobin leads to the formation of
carboxylhaemoglobin (COHb) reduces the oxygen carrying
capacity of blood.
• At concentration of 100 ppm people experience dizziness and
headache.
• The cigarette smoke contains 400 to 450 ppm CO the percentage
of COHb in blood of cigarette smokers increases with increase in
smoking.
• At concentration of 750 ppm of CO it will cause death.

56. Carbon Monoxide
(COHb)

57. • Effects on plants:-
• CO reduces nitrogen fixing capacity of bacteria. Which affects the
plant growth.
• High concentration of causes leaf drops, reduces the size of leaf
and ageing
• Effects on materials:-
• Carbon monoxide appears to have no detrimental effect on
materials.

58. Oxides of Sulphur
• Effects on human health:-
• It causes irritation of eyes and respiratory tracts.
• Increase in SO2 concentration in the atmosphere, may lead to lung
cancer
• SO2 may obstruct breathing
• SO2 leads to the formation of H2 SO4 which is 20 times more
irritant than SO2

59. • Effects on Plants:-
• The low concentration for long period may cause discoloration of
leaves
• SO2 affects the growth of plants
• At high concentration the leaf tissues gets damaged.
• H2SO4 is extremely toxic to plants and soil fertility.

60. Effects on Plants

61. • Effects on Materials:-
• The sulphuric acid will attack building materials containing
carbonates. This will form CaSO4 the CaSO4 gets easily washed
away leaving discolored surface
• Paper absorb SO2 causing the paper to become brittle
• Leather looses the strength and flexibility.

62. Acid Rain

63. Oxides of Nitrogen
• Effects on Human Health:- Nitric Oxide reduces the Oxygen
carrying capacity of blood.
• Nitrogen dioxide causes irritation of lungs
• High level of NOx causes pneumonia, lung cancer, oxygen
deficiency.
• NOx causes irritation of respiratory system, nervous system and
digestive tracts.
• NOx is extremely dangerous to human health.

64. Oxides of Nitrogen
Irritation of lungs
lung cancer

65. • Effects on Vegetation:-
• NO2 and primary pollutants can damage plant tissues
• High concentration of NO Causes Damage to leaves.
• Secondary Pollutants such as smog, O3 may damage the vegetation
• Effects on Materials:-
• Nitric acid causes corrosion to metal surface
• NO2 fades the color of clothes
• NO2 causes cracking of rubber
damaged plant tissues
Corrosion

66. Hydrocarbon
• Effects on human health:-
• Aromatic hydrocarbon may lead to cancer
• Inhalation of hydrocarbon causes irritation of respiratory tract.
• Methane creates narcotic effects on human beings
• Most of the hydrocarbon are carcinogenic to lungs
irritation of respiratory tract

67. • Effects on Vegetation:-
• HC affects plant growth
• Discoloration of leaves
• Effects on Materials:-
• It causes discoloration of materials
• Material becomes less elastic and more brittle.
Discoloration of leaves

68. Harmful Impacts of Air Pollution on Plants

69. Harmful Impacts of Air Pollution on
Human beings

70. Harmful Impacts of Air Pollution on
Human beings

71. Harmful Effects of Air Pollutants on
Human Health

72. Harmful Effect of Air Pollution on Material

73. Control of Air Pollution
• Air pollution cannot be fully abated but can be
controlled if certain measures are taken.
• Controlling measures for air pollution can be mainly
divided into
• Preventive measures
• Control measures
• i.e. Control of gaseous/ particulate pollutants
• From industry/ automobiles using equipments

74. Preventive Measures
• These measures are mainly aimed at correction right at
the source so there will be lesser amount of pollutant
emitted from the industry/ automobiles.
• Some of the important preventive measures are
• Using low sulphur coal in power plants
• Using natural gas in place of coal for power generation.
• Using LPG/ CNG instead of diesel or petrol in
automobiles.

75. Preventive Measures
• “Modifications” in industrial processes and/ or
equipments to reduce the emissions
• Section of suitable site and zoning for industrial unit:
Zoning means setting aside separate areas for
industries so that they are far from residential areas.
This will help in proper dispersion of pollutants
resulting in lower concentration of pollutants in the
air of residential area.
• By using proper environment impact studies before
setting the industry.

76. Control Measures
• The most common method of eliminating or reducing pollutants
to an acceptable level includes:
• Collecting the pollutants by using equipments to prevent its
escape into atmosphere.
• Destroying the pollutants by thermal or catalytic combustion
• Changing the pollution to less toxic form.
• By releasing the pollutants through tall chimneys for greater
dispersion. Tall chimneys will liberate the pollutants beyond
the inversion layer there by reducing the concentration of
pollutants near the source. But the liberated pollutants will
settle somewhere and cause of the air pollutants even far away
from the source.

77. Control Of Air Pollution
Prevention is always better than cure.
• one can prevent the air pollution. For this purpose some of the examples
are as follows:-
• (i) Controlling the spread of coal dust by sprinkling water on it before
handling in a thermal power plant.
• (ii) Preventive maintenance by repairing leaky valves in advance so as to
prevent the leakages of the harmful gases in air.
• (iii) Applying zoning to distribute the impact of air pollution in a
community.
• (iv) Selection of proper material. For example using low sulfur coal
reduces the problem.

78. Control Of Air Pollution
• In addition to the preventive measures one has to have
control technologies as follows.
• Depending upon the situation different control technologies
are adopted. For dealing with the particulate matter the
following control technologies are used,
• Settling chambers
• Cyclone separators
• Fabric filters
• Electrostatic precipitators
• Wet collector (scrubbers)
• The first two of the above are used for coarse particulates
where as the other three are used for fine particulates.

79. Air pollution Control
• The atmosphere like a river, do possesses self-
cleansing properties, which continuously clean and
remove the pollutants from the atmosphere under
natural processes. So long as the pollutants discharged
by man into the environment, is lower than the
natural cleansing capacity of the environment, we live
happily without any air pollution. But as when the
discharged pollutants exceed the natural cleansing
capacity, our environment becomes polluted, Attempts
are then made to reduce the emission of pollutants
from the automobiles of factories by adopting
mechanical means, or by using high rise chimneys for
better dispersion and dilution of pollutants over a
longer range of environment..

80. The Natural Self-Cleansing Properties
of the Environment
• The Various natural properties, which continuously
clean the environment, automatically, are:
• Dispersion
• Gravitational Settling with or without flocculation of
particles
• Absorption including washout and scavenging;
• Rainout and
• Adsorption
• All these processes, naturally occur periodically in the
ambient air, thereby removing or reducing the various
pollutants entering the air. These processes are briefly
discussed below:

81. Dispersion
• Dispersion of pollutants by winds reduces the
concentration of air pollutants at one place,
although in the strict sense, it does not remove them
from the environment as a whole. This mechanism is
therefore a diluting mechanism only.
• The dispersion through long chimneys, dilutes the
air pollutants near their source only, and does not
reduce their long term undesirable effect on the
community as a whole.

82. Dispersion

83. Gravitational Settling
• Gravitational setting is the most important natural
mechanism, under which large heavy particles from
ambient air settles down on buildings, trees and
other objects. This generally happens for the
particles which are larger than 50 µm in size.
• This process also helps in removing flocculated
particles formed by uniting of smaller particles over
larger particles, till a floc particle, large and heavy
enough to settle out under gravity, is formed.

84. Gravitational Settling

85. Absorption
• In the natural absorption process, the gaseous as well
as particulate pollutants from the air get collected in
the rain or mist, and may settle out with that moisture.
This phenomenon takes place below the cloud level,
when falling raindrops absorb pollutants, and is also
known as washouts or scavenging. The process,
however, does not help in removing particles smaller
than 1 µm in size.
• The gaseous pollutants are removed in dissolved state
with moisture, either with or without chemical
changes.

86. Absorption

87. Rainout
• Rainout is the process involving precipitation above
the cloud level, where submicron particles present
in the atmosphere in the cloud, serve as
condensation nuclei. Around which drops of water
may form, and fall out as raindrop. This
phenomenon helps in increased rainfall and fog
formation in urban areas, containing huge quantity
of such particles, raising high above the cloud level.

88. Adsorption
• Adsorption is the phenomenon in which the gaseous,
liquid or solid pollutants present in the ambient air are
kept attached, generally electrostatically, by a surface,
where they are concentrated and retained. Natural
surfaces, such as soils, rocks, leaves, blades of grass,
buildings, and other objects can adsorb and retain
pollutants. The particles may come in contact with such
surfaces either by gravitational setting or by inertial
impaction, under which the pollutants are carried to
such surfaces by winds. Impaction is particularly
effective for particles of size 10 to 15 µm.

89. Dilution Method for Controlling Air
Pollution from Stationary Sources
• Transporting the pollutants over larger distances, and
thus, reducing the pollution near the emission source.
• This method is largely adopted in developing countries,
because here the pollution is generally confined over
smaller environment near cities and industrial towns
only. The neighbouring environment, which is free from
emission, is thus made to share some of the pollutants
burden, thereby causing somewhat equitable
distribution of the pollutants. Nevertheless, this method
only reduces the concentration of pollutants at
particular place (s), rather than reducing or removing
the pollution load from the total environment, as a
whole.

90. Controlling Air Pollution from Stationary
Sources by Installing Engineering Devices
• In order to reduce the pollution load entering the
environment from stationary sources, several
measures may be taken; out of them,
replacement of burning fuel by electricity or
solar energy is by far, the best method, as it will
eliminate the vary production of pollutants in the
combustion process. Besides this we can make
use of better quality of fuels and efficient
engines, for reducing pollution loads from
emissions. Say for example, LPG and LNG may be
used in industries in place of coal, as they will
produce much less pollutants in emission.

91. Controlling Air Pollution from Stationary
Sources by Installing Engineering Devices
• Replacement of old obsolete processes in industries
with the new efficient processes may also lead to
reduce pollution emissions. Besides such innovations
and precautions, certain mechanical devices may be
installed in the industrial processes, which may help
in reducing the emission of pollutants.
• Such mechanical devices, are generally divided into
two categories; i.e.
• (i) those devices which help in reducing particulate
matter; and
• (ii) those devices which help in reducing gaseous
pollutants.

92. Control of Particulate Matter in Industry
• The important devices, which are used to control
particulate matter are;
• (a) Gravitational Settling chambers
• (b) Centrifugal collectors including cyclone
collectors and dynamic precipitators.
• (c) Wet Scrubber including spray towers, wet
cyclone scrubbers and venturi-scrubbers.
• (d) Electronic Precipitators;
• (e) Fabric Filters.

93. Gravitational Settling Chamber
• It is used to remove particles with size greater than 50µ m. Velocity
of the flue gas is reduced in large chamber thereby inducing
settling the particles under gravitational force. Settling is governed
by stokes law.
• The usual velocity of the flue gas through settling chambers is
between 0.5 to 2.5 m/s.
• The largest sized particles (d) that can be removed with 100 %
efficiency in such chamber of length L and height H is given by
equation.

94. Gravitational Settling Chamber
• The above equation applies to quiescent condition
but quiescent condition cannot be maintained in a
flow through settling chamber, so a correction factor
is applied and eqn becomes.

95. Gravitational Settling Chamber

96. Gravitational Settling Chamber

97. Advantages of Settling Chamber
• Low Initial Cost.
• Simple to design
• Low pressure drop
• Low Maintenance cost
• Dry and continuous disposal of solid particulates.

98. Disadvantages of Settling Chamber
• The collection efficiency can be increased by
providing the baffles and horizontal baffles/
tray in the chamber to reduce the settling
path.
• Settling chambers are used widely for
removal of large solid particulates from
natural draft furnace, kiln, etc.. They are also,
sometimes used in the process industries,
particularly the food and metallurgical
industries, as first step in dust control.

99. Cyclone Separator
• Centrifugal force is utilized to separate the particulate matter from the
gas. As Centrifugal force is much greater than gravitational force smaller
particles can be removed. (10 to 50 µm)
• A cyclone is a specially designed closed chamber, in which the velocity of
the inlet gas is transformed into spinning vortex, and the particles from
the gas are thrown out under the centrifugal force. The particles thrown
out on the walls of the chamber, slides down to the hopper and thus
removed. Its efficiency depends on the centrifugal force generated, which
in turn, depends on the mass of a particular(Mp) , inlet gas velocity Vi and
radius of cyclone (R) and is given by the eqn
• Its collection efficiency is in between 50 to 90 %

100. Cyclone Separator

101. Cyclone Separator

102. Cyclone Separator

103. Advantages of Cyclone Separators
• Low Initial Cost
• Requires less floor area
• Simple construction and maintenance
• Low to moderate pressure loss (2.5 to 20 cm)
• Can handle large volume of gas at high temperature.
• Dry continuous disposal of collected dust.

104. Dis-advantages of Cyclone Separators
• Requires large head room
• Less efficiency for smaller particles (< 10 µ)
• It is subjected to severe abrasive deterioration.
• Quite Sensitive to variable dust load and flow rates.
• Cyclones are widely used in industries producing
larger quantities of gas containing larger sized
particles like, cement and fertilizer industries,
petroleum refineries, grain mills and textile industries.
• Cyclone can be arranged in series and in parallel to
increase the efficiency of collection compare to a
single large sized cyclone.

105. Electrostatic Precipitators
• It works on the principle of electrical charging of
the particulate matter(-ve Charge) and collecting it
on a differently charged (+ve charged) collecting
surface. It has a very high efficiency of about 99 %
and can remove particles in the size range of 0.1 µm
to 1 µm efficiently.

106. Electrostatic Precipitators

107. Electrostatic Precipitators

108. Advantages of Electrostatic Precipitators
• High Collection Efficiency
• Particles as small as 0.1 µm can be removed
• Particles may be collected dry or wet.
• They can be operated at high temperature up to
300- 450 0C
• Maintenance is nominal, unless corrosive and
adhesive materials are present in the flue gases.
• Few moving parts.
• Treatment time is negligible (0.1 – 10 S).

109. Disadvantages of Electrostatic
Precipitators
• High Initial Cost.
• They use high voltage, and hence may pose risk to
personal safety of the staff.
• Possible explosion hazards during collection of
combustible gases or particulates.
• Collection efficiency reduces with time.
• Space requirement is more because of the large size
equipments.
• They are widely used in thermal power plants, cement
factories, paper and pulp industries, mining and
metallurgical industries, iron and steel industries,
chemical industries etc.

110. Fabric Filters
• In this device, fabric filter’s out the particulate matter from
the gas stream and allow clear gas to flow. In such a system,
the flue gas is allowed to pass through a woven or felted
fabric, which filters out the particulate matter and allows the
gas to pass. Small particles are retained on the fabric, initially
through interception and electro-static attraction; and later
on, when a dust mat is formed, the fabric starts collecting
particles more efficiently it can remove particles up to 1 µm.
Its efficiency is around 99 %.

111. Fabric Filters
• A bag house filter provided in an ordinary room
of the factory, contains several vertically hanging
fabric cylindrical bags (1.8 to 9m long) ; the
upper ends of the bags are closed, and lower
ends are attached to a hopper, where the inlet of
the flue gas is also located. The upwards moving
gas drops out particulate matter in these bags,
which settles down in to the hopper, and cleaner
gas goes out through the fabric filters. The
framework, housing the hanging bags, is
provided with a automatic shaking device for
removing the collected dust.

112. Fabric Filters

113. Advantages of Fabric Filters
• High collection efficiencies for all particle sizes,
especially for particles smaller than 10 µm in
diameter.
• Performance decrease becomes visible, giving
prewarning.
• Nominal power consumption
• Dry disposal of collected particles.

114. Dis-advantages of Fabric Filters
• High temperature gases need to be cooled to the
range within which filter are stable.
• High maintenance and fabric replacement cost.
• Large size equipments.
• The fabric is liable to chemical attack.

115. Fabric Filters

116. Scrubbers
• In scrubbers the particulate matter are incorporated into
liquid droplets and thus are removed from the gas stream.
Different types of Scrubbers includes.
• (a) Spray towers
• (b) Venturi Scrubbers
• (c) Cyclone Scrubber
• In these devices the flue gas is made to push up against a
down falling water current. The particulate matter mixes up
with water droplets and thus, falls down and get removed.
• Water solution, when mixed with aqueous chemical
solutions, like lime, potassium carbonate, slurry of MnO and
MgO, etc., do help in removing gaseous pollutants also from
the flue gases.

117. Cyclone Scrubber

118. Spray Towers

119. Venturi Scrubbers

120. Advantages of Scrubbers
• They can simultaneously remove particulate and
gaseous pollutants.
• Hot gases can be cooled down
• There is no particles re-entrainment
• Corrosive gases can be recovered and neutralize.
• The separated gases through contact with aqueous
chemicals may produce useful byproducts, as
chemicals and fertilizers.

121. Disadvantages of Scrubbers
• A lot of wastewater needing disposal may be
produced.
• Wet outlet gases cannot rise high from the stack.
• Poses freezing problems in cold countries.
• Maintenance cost is high, when corrosive materials
are collected.

122. Control of Gaseous Pollutants
• For gaseous pollutants the following control
technologies are used.
• Absorption
• Adsorption
• Combustion
• For the control of gases such as NO2 and SO
produced in combustion, wet and dry scrubbers are
used.

123. Control of Gaseous Pollutants
• The gaseous pollutants can be controlled through the
techniques of combustion, absorption and adsorption.
• (a) In combustion process oxidizable gaseous pollutants are
completely burnt at a high temperature. This processes is
used to control gaseous pollutants in petro-chemical,
fertilizers, paint and varnish industry.
• (b) In absorption techniques effluent gases are passed
through absorbers containing liquid absorbents that remove,
treat or modify one or more gaseous pollutants. Liquid
adsorbent may utilize either chemical or physical change to
remove pollutants.
• In Adsorption, the air pollutants are adsorbed on a solid
surface. Commonly used adsorbents are activated carbon,
activated alumina, silica gel etc..

124. Control of Gaseous Pollutants
Combustion or Incineration
• Combustion or Incineration Equipments may be
used to purify polluted gases, when the pollutants in
the gas stream are oxidisable to an inert gas.
Pollutants, like hydrocarbons and carbon monoxide
(CO) can be easily burnt, oxidized, and removed in
such equipments.
• Both Direct flame combustion by afterburners and
catalytic combustion have been used in commercial
applications.

125. Control of Gaseous Pollutants
Absorption Units
• The absorption units work on the principle of transfer of the
pollutants from the gas phase to the liquid phase. In other words,
the pollutants from the dirty gas, get absorbed in the liquid,
through which the gas is made to pass, in these units. Such
absorption takes place by diffusion as well as dissolution.
• The effectiveness of these devices, naturally depends upon the
solvent, through which the gas is made to pass.
• Absorption Units Like Spray towers, plate towers, packed towers,
and venturi scrubbers. Out of these devices, spray towers and
venturi-scrubbers can simultaneously be used for removing
particulate pollutants. Scrubbers are generally less effective in
removing gaseous pollutants than towers, but then, towers get
frequently clogged by particulate matter.
• Other effective devices for removing gaseous pollutants, i.e. plate
towers and packed towers.

126. Control of Gaseous Pollutants
Adsorption Units
• Using adsorbents like activated carbon, molecular sieves, activated
alumina, silica gel, etc..
• In adsorption units, the dirty gas are made to pass through the beds
of such adsorbent materials, wherein the pollutants are effectively
caught and removed. Activated carbon beds can very effectively
catch hydrocarbons, H2S and SO 2
• The above adsorbents, except activated carbon, have the drawback
of preferably capturing water, before catching any of the gaseous
pollutants; and hence have to be removed from the gas, before it is
treated in such units.
• However, almost all the adsorbents are subjected to destruction at
moderately high temperature (150 0 C to 600 0 C) Hence they
prove to be very inefficient for purifying industrial gases at such
high temperature.

127. Control of Automobile Exhaust
Automobile Exhaust can be controlled by:
• (a) The un-burnt hydrocarbon in automobile emission can be
reduced by use of efficient engines (MPFI, CRDI, TDI
technologies).
• (b) Catalytic converter can convert NO to Nitrogen gas and
reduce potential hazards.
• By enforcing stringent emission standards for the vehicles like
Bharat Stage 4 or Euro 4 right at the manufacturing stage.
• Using lead free petrol.
• By using cleaner fuel like CNG, hybrid car, electric car, etc..
• By proper maintenance of the vehicles
• Developing good mass transportation facilities.

128. Control of Automobile Exhaust

129. Control of Automobile Exhaust

130. Notations
• parts-per-million (ppm) 10–6, parts-per-billion (ppb) 10–9, and
parts-per-trillion (ppt) 10–12 level

131. Case Study: Air Pollution Episode
Bhopal Gas Tragedy
• The Story of Bhopal Gas Tragedy: The Lucky Ones Died That
Night
• It was five minutes midnight in Bhopal on December 2 1984.
The congested city was asleep and the winter air was heavy.
Many had gone sleep. It was all quite, but the city was to change
forever.
• Suddenly, 27 tons of lethal gases including methyl Isocyanate
(MIC) started leaking from Union Carbide’s Pesticide factory.
The cloud of gases rapidly blanked the city.
• Grossly under designed safety systems were either
malfunctioning, under repair, or had been switched off as part
of a cost cutting exercise. The warning siren at the factory had
reportedly been turned off. It was the world’s worst Industrial
Disaster.

132. Case Study: Air Pollution Episode
Bhopal Gas Tragedy
• Here is a survivor’s account of what happened on
that ill fated night:
• “ The poison cloud was so dense and searing that the
people were reduced to near blindness. As they
gasped for breath its effects grew more suffocating.
The gases burned the tissues of their eyes and lungs,
and attacked their nervous systems. People lost
control of their bodies Those who escaped with their
lives are the unlucky ones; the lucky ones are those
who died that night.”

133. Case Study: Air Pollution Episode
Bhopal Gas Tragedy
• 70,000 people were evacuated from the area after
the accident and 2,00,000 more fled in panic. The
effect of the gas was felt up to 100 sq km from the
factory. More than 8000 people died in the few days
following the disaster. Within few months death toll
raised to 20000 due to exposure related illness.
• The gases affected more than 5,00,000 people,
leaving them with the life time of ill health and
trauma.

134. Bhopal Gas Tragedy

135. How did the accident occur?
• How did the accident occur?
• Most probably water entered the storage tank and
caused a runway chemical reaction that led to an
increase in temperature, which converted the liquid
MIC into gas. Investigations reveled that there had
been six early accidents in the plant and that
workers had complained off exposure to dangerous
substances. Yet proper safety mechanisms were
allegedly not put in place.

136. Bhopal Gas Plant

137. Bhopal Gas Plant

138. Case Study: Air Pollution Episode
Bhopal Gas Tragedy
• Union Carbide accepted only moral responsibility for the
disaster and not any liability. The Government of India
filed a case against the company for US $ 3 billion, but
strangely accepted US $470 million as settlement in
1989. Nearly 95 % of the survivors had received just Rs
25000 for lifelong injury and loss of livelihood. That
works out to be 9 US cents a day for more than 20 years
of Unimaginable suffering.
• A criminal case was filed in the court of Bhopal against
Union Carbide, and its then chairmen Warren Anderson
for negligence,. They did not attend the court
proceedings and Anderson has been proclaimed a
fugitive from justice by the court.

139. Bhopal Gas Tragedy

140. What does the story of the Bhopal
Tragedy Tell us ?
• The tragedy shows that poor communities are
disproportionately affected by toxic materials
discharged into air, land and water. When a crisis
occurs, or an accident occurs these people cannot
get justice from the polluters, or the governments.
Source: Basics of Environmental Studies By R. Rajgopalan

141. Exam Questions
• What is Air Pollution? Explain in detail its effects on property
and materials.
• Explain primary and secondary air pollutions. State the effects
of air pollution on plant and material.
• Explain the effect of air pollution on men, material and
animals.
• Describe different primary and secondary air pollutants.
• Write a S.N. on Electrostatic precipitator.
• Describe the devices used for control of particulate matter.

142. References
Sewage Disposal and Air Pollution Engineering :
By Prof S.K. Garg
Khanna Publishers
Internet Websites

143. Thanks…
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