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1. AIR POLLUTION
Unit-1
Mekelle Institute of Technology,
BY Brhane Amha

2. CONTENTS
•Definition
•Composition of atmospheric air,
Classification and sources of air pollutants
•Air pollution sinks
• Effects of air pollution on human, plant and
material
•Air pollution control methods and
• Air control equipments.

3. WHAT IS POLLUTION ???
 Pollution is “change in background conc.”.
 Pollution broadly refers to the presence of
undesirable substances in the environment
which are harmful to man and other
organisms.
 The presence of unwanted substances in the
environment may occur due to the human
activity discharging byproducts or waste
products released due to industries.
 Pollution happens because no process is 100%
efficient; each process produces pollution.

4. AIR POLLUTION
 Air pollution defined as the presence of foreign
substances in the air at a concentration that will
adversely affect to human, animal or plant life,
or property of the individual.
or
 Chemicals added to the atmosphere by natural
events or human activities in high enough
concentrations to be harmful to human, animal
or plant life, or property of the individual.

5. Atmosphere as a Resource
Composition of the dry air
in the lower atmosphere
Nitrogen 78.08%
Oxygen 20.95%
Argon 0.93%
Carbon dioxide 0.04%
Trace gases >0.02%
(He,CO,NO2, SO2,H2, NH3)
Ecosystem services
Blocks UV radiation
Moderates the climate
Redistributes water in the
hydrologic cycle

6. Pollutant
•The term Pollutant refers to a substance which
increases in quantity in the air and adversely affects
the environment.
•Examples are carbon monoxide, sulfur dioxide, lead,
Nitrogen dioxide etc
•Contaminant is a substance which is not present in
nature, but released due to human activity.
•Examples are DDT (Dichlorodiphenyltrichloroethane),
Malathion, PVC etc

7. SOURCE AND CLASSIFICATION
OF POLLUTANTS
The sources that contribute to air pollution may be
broadly classified in two types
o Natural Sources
 Man- made or anthropogenic Sources
 Natural- pollen grains, volcanic eruptions, forest
fires, dust storms, spores, bacteria and other
microorganisms. The problem of pollution due to
natural sources in general considered to be minimal.
 Man- made- industrial units, thermal power plants,
automobile exhausts, fossil fuel burning, mining,
nuclear explosions. The problem of pollution due to
man made in general considered to be maximal.

8. SOURCE AND CLASSIFICATION
•Stationary
It include smoke stacks of power plants,
manufacturing facilities (factories) and waste
incinerators, as well as furnaces and other types of
fuel-burning heating devices.
Mobile
It include motor vehicles, marine ships, Trains, and
aircraft.

11. Air pollution Sinks
Sinks: Things or Activities that remove pollution from the air
are called Air pollution sinks
or
Vehicles for removal of a chemical or gas from the
atmosphere-biosphere-ocean system.
Example are
•Oceans
•Trees
•Winds
•Chemical processes
•Deposition
•A carbon sink, for example, might be the ocean (which
absorbs and holds carbon from other parts of carbon cycle) or
photosynthesis (which converts atmospheric carbon into plant
material).

12. Air pollution Sinks
Sinks are a fundamental factor in the ongoing
balance which determines the concentration of
every air pollutants in the atmosphere.
• If the sink is greater than the sources of a gas, its
concentration of pollutants in the atmosphere will
decrease
• if the source is greater than the sink, the
concentration of pollutants will increase

13. AIR POLLUTANTS
 Substance dwelling temporarily or permanently in the air.
 Alters the environment by interfering with the health, the
comfort, or the food chain, or by interfering with the
property values of people.
 A pollutant can be solid (large or sub-molecular), liquid or
gas .
 It may originate from a natural or anthropogenic source
(or both).

14. CLASSIFICATION OF POLLUTANTS
Air pollutants are classified based on origin, chemical
composition and state of matter.
Classification based on origin
Air pollutants can be grouped into two categories:
(1)Primary pollutants, Harmful substances
which are emitted directly into the
atmosphere and present there as such(i.e
in the form they are originally emitted).
Primary air pollutants contribute to as much
as 90% global air pollution.
(2)Secondary pollutants, which are produced in
the atmosphere when certain chemical reactions
take place among primary pollutants.

15. PRIMARY POLLUTANTS
The major primary pollutants include:
 particulate matter (PM),
 sulfur dioxide,
 nitrogen oxides,
 volatile organic compounds (VOCs),
 carbon monoxide,
 Pollen grains, bacteria and
 lead.

16. Major Air Pollutants

19. SECONDARY POLLUTANTS
 Some primary air pollutants react with one
another or with other chemicals to form
secondary pollutants.
 Examples are Peroxyacetyl nitrate(PAN),
formaldehyde, Ozone and smog.

21.  Atmospheric sulfuric acid is one example of a
secondary pollutant.
 Air pollution in urban and industrial areas is often
called smog.
 Photochemical smog, a noxious mixture of
gases and particles, is produced when strong
sunlight triggers photochemical reactions in the
atmosphere.
 The major component of photochemical smog is
ozone.

22. Classification based on chemical composition
 According to chemical composition, air
pollutants are categorized as organic and
inorganic.
 Organic air pollutants: These Pollutants are
mainly composed of carbon and hydrogen. In
addition, oxygen, nitrogen, sulfur and
phosphorous may also be present.
 Eg. Hydrocarbons, organic sulfur compounds,
aldehydes, ketones, Carboxylic acids
 Inorganic air Pollutants: These are purely
inorganic in nature.
 Eg. Carbon dioxide, carbon monoxide, oxides
of sulfur, oxides of nitrogen.

23. Classification based on state of matter
 According to state in which they exist
particulate and gaseous, air pollutants are
categorized as Particulate and Gaseous.
 Particulate air pollutants: The solids and
liquids dispersed in the atmosphere constitute
the particulate air pollutants.
 Solid particulates: Eg. Dust, Fly ash, Smoke,
Liquid particulates: Eg. Fog, Spray, Mist
 Gaseous air Pollutants: These are organic and
inorganic gases that are present in the air as
pollutants.
 Organic gases Eg. Methane, butane,
aldehydes
 InOrganic gases Eg. SO2, NO2, NH3,H2S

24. MAJOR POLLUTANTS SOURCES AND
EFFECTS
 Carbon monoxide (CO)- colorless, odorless, tasteless
gas.
 No effect at normal conc. (0.1ppm)
but higher conc. seriously affect.
 Volcanoes, natural gas emissions,
seed germination contribute to CO.
 Transport sector contribute 75% CO.
Residential wood burning 10%, industrial process
15% CO.

26. Effects:
 Reduce oxygen carrying capacity of blood.
 Decrease in vision and causes cardio vascular
disorders.
 Carbon dioxide (C02)- Fossil fuel combustion.
 Jet plane use O2 and release CO2.
Burning
Effects:
 Causes headache and nausea.
 Effect on climate, increase global temp.

27.  Oxides of nitrogen – NOx group contains NO, NO2, N2O.
 Fuel combustion in automobiles and industries.
 Lightening.
 Forest fires.
 Natural ionizing radiations.
Effects:
 Reduce blood carrying capacity.
 Causes lung problems.

29.  Oxides of sulphur – generally called SOx, include SO2,
SO3.
 67% SOx pollution due to volcanic activities and other
natural sources.
 Remaining due to fossil fuel burning, transportation.
 Industrial activities.
Effects:
 Respiratory problems
 Marbles, clothes, paper, leather also affected.
 Plants also heavily affected.

31.  Hydrocarbons (HC) – these include methane, ethylene,
acetylene, terpenes etc.
 Sources include coal fields, natural fires.
 Incomplete combustion
 Forest fires
 Agricultural burning
Effects:
 Carcinogenic effect
 Form ozone and PAN which are harmful.
 Damage plants, rubber materials, fabric and paints.

32. PARTICULATE MATERIALS
 Particles of different substances suspended in the
air
 In the form of solid particles and liquid droplets
 Particles vary widely in size
 Different particulate materials are aerosols, dust,
smoke, fumes, mist, fog, fly ash etc.

33.  Fine particles come from a variety of sources:
-diesel trucks and buses
-construction equipment
-power plants
-woodstoves
-wildfires
 Also, Chemical reactions in the atmosphere can
transform gases into fine particles.

35. Effects:
 Premature death
 Aggravated asthma
 Acute respiratory symptoms
 Chronic bronchitis
 Decreased lung function (shortness of breath)
 People with existing heart and lung disease, as well
as the elderly and children, are particularly at risk

36. FACTORS AFFECTING HUMAN HEALTH
 Nature of the pollutants
 Concentration of the pollutants
 Duration of exposure
 State of health of person or receptor
 Age group of the person or receptor

37. EFFECTS OF AIR POLLUTION ON HUMAN

38.  Pollutants present in the air often cause harmful
effects. The nature of pollutant, its concentration and
duration of exposure are among the factors affect the
human health.
 In general infants, eldery people are those with
respiratory diseases are more susceptible to air
pollution. Adverse effect is maximum in winter
compare to other seasons.
 around 30-40% of cases of asthma and 20-30% of
all respiratory disease.
 effect our health in many ways with both short term
and long term effect.
 Short term effect are: irritation to nose, eye,
throat, bronchitis, headache etc.
 Long term affect are: lung disease, chronic
respiratory problem, damage to heart, brain, eyes
etc.

39.  Gaseous pollutants like H2S, SO2, NO2 and
hydrocarbons cause odor nuisance.
 Eye irritation due to NOx, O3, PAN,
particulates.
 Nose and throat due to SO2, NOx etc.
 Irritation of respiration tract caused by SOx, NOx,
CO, O3 causes increase in mortality.
 High conc. of SO2, NO2 and SPM causes
bronchitis and asthma.
 CO and NO react with haemoglobin and reduce O2
carrying capacity of blood.
 Heavy metals like lead can cause poisoning. High
conc. cause damage to liver and kidney.

40. EFFECTS OF AIR POLLUTION ON PLANT

41.  Decrease yield in agriculture.
 Suppressed growth of vegetables.
 Leaf injury and damage to young plants.
 Decreased growth rate and increased death
rate.

42.  The major pollutants affecting plants are SO2,
NO2, O3, Florides, ammonia and ethylene. They
may damage the plants to varying degrees as
given in Table

43. EFFECTS OF AIR POLLUTION ON MATERIALS
 Air pollutants cause immense damage to various
materials like stone, metal, paint work, fiber material,
glasses, rubber and textiles.
 Corrosion of metals due to SO2 in presence of oxygen
and moisture is converted into H2SO4 acid.
 H2SO4 acid react with limestone, marble and other
building materials to cause deterioration.
 Soiling and eroding of building materials.
 SO2, O3, H2S and aerosols damage protective coating
and paints of the surface.
 O3 and PAN causes cracking of rubber and various
electrical insulations.
 Deterioration of art work due to SPM (suspended
particulate matter).

44. AIR POLLUTION CONTROL
 Cannot be fully prevented but can
be controlled.
1. Preventative measures
2. Control measures using equipments.
Preventative measures (source control)
 Selection of suitable fuel. (Low sulphur coal in power
plant, using of CNG)
 Modification in industrial process.
 Selection of suitable site and zoning for industrial unit.

45. Control measures
 When source control not possible some measures
taken to prevent pollution.
 Collecting pollutants by using equipments.
 Destroying the pollutants by thermal or catalytic
combustion.
 Changing the pollutants to less toxic form.
 By releasing the pollutants through tall chimneys for
greater dispersion.

46. PREVENTATION BY LAWS
 Various laws has been established for the menace
of air pollution.
 Air (Prevention & control of pollution ) Act,1981.
 Air (Prevention & control of pollution ) Amendment
Act,1987.
 Motor vehicle Act, 1988.
 Air (Prevention & control of pollution) Union
Territories Rules, 1983.
 Environment Protection Act, 1986.

47. The government is trying to
 remove the use of leaded petrol, a major
cause of air pollution.
 the industrial acts are implemented to control
the harmful emission of gases.
 the natural management team work to
minimize the effect of various natural disaster
like forest fire, volcanic eruption that are
causes of air pollution.

48. AIR POLLUTION CONTROLLING EQUIPMENTS
 In general, greater emphasis is given to control
particulate air pollutants, may be because they are
visible.
 The important devices/equipments used to control
particulate pollutants are
 Gravity settling chambers
 Cyclone separator
 Dynamic precipitators
 Electrostatic precipitators
 Fabric filters
 Scrubbers

49. AIR POLLUTION CONTROLLING EQUIPMENTS
 Gravitational settling chamber
 Settling chambers are the oldest and very simple type of
equipment used for collection of solid particles.
 As the air is passed through the chambers at a low
velocity, the dust Particles (size 40-100 μm diameter) settle
by gravitational force and the clean air comes out.
 Used to remove particles with size greater than 50 μm.

50. Advantages
 Low initial cost.
 Simple technique
 Easy to design.
 Low pressure drop.
 Low maintenance cost.
 Dry and continuous disposal of solid particulates.
Disadvantages
 Require large space.
 Less collection efficiency.
 Only larger size particles can be collected, it is
not possible to collect or settle smaller size dust
particles.

51. Cyclone separator
Cyclone seperators also operate
on the principle of gravity
settlement.
The equipment mainly consist of a
vertically placed cylinder with
inverted cone attached to its base.
As dust air enters the cylinder, it
takes helical path downwards. Due
to rapid spiralling movement of the
air, the particles are thrown toward
the walls by centrifugal force.
Centrifugal force is utilized to separate the particulate matter.
It can remove 10 to 50 μm particle size.
Used mostly in industries.

52. Advantages
 Low initial cost.
 Require less floor area.
 Simple construction and maintenance.
 Can handle large volume of gas at high temp.
Disadvantages
 Requires large head room.
 Less efficiency for smaller particles (<10μm).
 Sensitive to variable dust load and flow rate.

53. Dynamic Precipitators
Dynamic precipitators work on
principle of centrifugal force
generated by rotating blades.
The dust particles of the air are
concentrated on the rotating blades
from where they are collected in a
concentrated stream.
Centrifugal force is utilized to separate the particulate matter.
It can remove 5 to 20 μm particle size.
Used mostly in industries.

54. Advantages
 Low initial cost.
 Require less floor area.
 Simple construction and maintenance.
 Can handle large volume of gas at high temp.
Disadvantages
 Less efficiency for smaller particles (<5 μm).
 Dynamic precipitators are not suitable for
sticky or fibrous dust particles, as they stick
to the blades.

55. Electrostatic precipitators (ESPs)
 Electrostatic precipitators are very efficient and versatile.
 Works on the principle of electrical charging of
particulate matter (-ve) and collecting it in a +ve charged
surface.
 An ESP consists of a thick cylinder fitted with an inlet at
bottom and an outlet at the top. An electrode –Ve and + Ve
charged electrode plates are placed at the sides,
 as the dust air passes through ESP, the negatively charged
metal grid provides –ve charge to smoke particle and smaller
charged particles are attached to oppositely charged
electrodes which gradually fall down to the bottom. The dust
free air comes out.
 99% efficiency.
 Can remove particle size range of 0.1 μm to 1 μm.

57. Advantages
 High collection efficiency.
 Particles may be collected dry or wet.
 Can be operated at high temp. (300-450˚c).
 Maintenance is normal.
 Few moving parts.
Disadvantages
 High initial cost.
 Require high voltage.
 Collection efficiency reduce with time.
 Space requirement is more.
 Possible of explosion during collection of
combustible gases or particulates.

58. Fabric filters
Fabric filters are the most
efficient and can separate
particles with size less than 0.5
μm in diameter.
As the air or gas is allowed to
pass through a woven Fabric,
the dust is trapped while the
gas passes out, which filters
out Particulate matter.
Small particles are retained
on the fabric.
Remove particles up to 1 μm.
Its efficiency up to 99%.

59. Advantages
 Higher collection efficiency for smaller
than 10 μm particle size.
 Performance decrease becomes visible, giving
prewarning.
 Normal power consumption.
Disadvantages
 High temp. gases need to be cooled.
 High maintenance and fabric replacement
cost.
 Large size equipment.
 Fabric is liable to chemical attack.

60. Scrubbers
 Particulate matters are passed through liquid stream
in a spray chamber, the pollutant (VOC) gets
transferred to the liquid. The sprayed liquid contains a
suspension of microorganisms , they will
biodegradation of pollutants (VOC) occurs and clean
air comes out from the spray chamber.
 Different types of scrubbers are-
- Spray tower
- Venturi scrubber
- Cyclone scrubber
 Particulate matter mix up with water thus falls down
and gets removed.

61. Spray tower
Cyclone scrubber

62. Advantages
 Simultaneously remove particulates and gaseous
pollutants.
 Hot gases can be cooled down.
 Corrosive gases can be recovered and neutralize.
Disadvantages
 Lot of waste waters produced.
 Poses freezing problem in cold countries.
 Maintenance cost is high when corrosive materials are
collected.

63. .
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