Environmental Management Studies

Lecture Series
By
Dr. Niharbala Devi
Professor
Dept. of Chemistry
ITER, Siksha O Anusandhan Deemed to be University
 Lesson -

AIR POLLUTION
 Causes of pollution problem
Pollution is the effect of undesirable changes in our surroundings
that have harmful effects on plants, animals and human beings
Two basic problems result from the consumption of resources for our
energy requirement
1. Resource Crunch
That results from irreversible depletion of resources exceeding the
carrying capacity of resources
1. Environmental degradation
That results from imbalances of our ecosystem exceeding the
assimilating ability of ecosystem thereby causing degradation in
environment
 Pollution problem
• Environmental degradation causes various pollution problem

• Degradation in air environment causes air pollution problem

• Degradation in noise environment causes noise pollution
problem
• Degradation in water environment causes water pollution
problem
• Dumping of solid waste in land causes land pollution problem
• Pollution affects the flora and fauna in various ways causing
ecological Pollution problem
 Nature of pollutant
1. Degradable pollutants: Easily degradable, Easily decomposed to
simpler compounds by means of biodegradation and physico-chemical
degradation. Most of the wastes released by living beings are
biodegradable. Most of the waste in our daily use are easily
degradable.
2. Difficultly degradable: These wastes are not easily degradable. They
take a long time to degrade. Examples are plastic waste,
chlorofluorocarbon, some pesticides etc
3. Non-degradable: These waste are not degradable to simpler
compounds. Examples are metallic waste. Toxic heavy metals like lead,
mecury,cadmium,chromium,nickel etc. will always remain the same
metal and hence toxic
 Types of air pollution
Natural air pollution and Anthropogenic air pollution

Natural air pollution

• Lightening: Atmospheric nitrogen and oxygen can react at high temperature of

lightening cause nitrogen oxide and nitrogen dioxide pollution

• Forest fire: Fire remnants of forest have the air pollution in the form of
particulates, unburnt hydrocarbon, carbon monoxide and some toxic pollutants

• Volcanic eruptions: Molten lava have the sulfur converted to sulfur dioxide and
can SO2 pollution
 Anthropogenic air pollution
• Use of fossil fuel like coal, crude oil, petroleum products cause air pollution
in the form of particulate pollution, SO2, NOx , CO, CO2 and other toxic
pollutants

• Vehicular pollution: particulate, CO, NOx

• Mineral excavation and beneficiation: particulate pollution

• Transportation: CO,CO2,SO2,NOx,other hazardous pollutants

• Loading and unloading: Particulate pollution

 Primary and secondary air pollution
Primary air pollution
• Pollutants that are emitted directly from identifiable sources are produced
both by natural and anthropogenic events.
• Examples are CO,CO2, SO2,NO,NO2, Particulates classified as PM10
(Particle size .<= 10 micron) PM2.5 (Particle size .<= 2.5 micron)
Secondary air pollution
• Pollutants that are formed by atmospheric chemical combination among the
primary pollutants and others
• Examples Acid particulates, Peroxy Acyl Nitrate (PAN) type of pollutants
 Common particulates

Besides technical names PM10 and PM2.5, the popular names of

particulate
• Aerosol: General term for particles suspended in air.
• Mist: Aerosol consisting of liquid droplets, eg. Sulfuric acid mist
• Dust: Aerosol consisting of solid particles that are blown into Dust storm
the air or are produced from larger particles by grinding them down
• Smoke: Aerosol consisting of solid particles or a mixture of solid
Cigarette smoke, smoke and liquid particles produced by chemical
reaction such from burning garbage as fires
• Fume: means the same as smoke but often applies Zinc/lead fumes
specifically to aerosols produced by condensation of hot vapors of metals.
• Plume: Geometrical shape or form of the smoke coming out of a chimney
• Fog: Aerosol consisting of water droplets
• Smog Term used to describe a mixture of smoke and fog
Dispersion of the pollutant in atmosphere-Factors
Meteorological factors Anthropogenic factors

Topography Position of the source

Wind speed Height of the chimney
Wind direction Concentration of pollutant in flue gas
Humiidty in air Flue gas temperature
Atmospheric pressure Flue gas flow
Atmospheric temperature Flue gas velocity
Lapse rate
Cloud cover
Solar insolation
 Effects of air pollution
• On human and animals: Respiratory problems like asthma, chronic bronchitis and
emphysema, carbon monoxide can reduce oxygen carrying capacity of blood,
gastrointestinal problems, toxic pollutants cause lung cancer, some air pollutants may
cause mutagenic disorders
• On vegetation: Cause damaging effect on leaves, cause excessive water loss, particulates
affect the photosynthetic activities, SO2 cause necrosis problem that is yellowing of
leaves and cause the flower to fall down
• On materials: Corrosion of structures and marble monuments
• Ozone layer depletion: Chlorofluorocarbon type chemical travel to stratospheric ozone
layer, initiate chain reaction destroy ozone layer allowing harmful ultra-violet radiation to
penetrate the atmosphere and cause cancer related problem
• Global warming: Green house gases (GHGs) like carbon dioxide, methane, nitrous
oxide etc. in the reflecting sun light from earth surface entrap long wave infrared
radiation raise the global temperature. Because of enormous increase in CO2 in
atmosphere, there has been continuous rise in global temperature. This
phenomenon cause drastic changes in climate, melting of ice cap, occurrence of
flash flood, rise in sea level, inundation of low lying area etc.
• Acid rain problem: This causes corrosion problem causing loss of material and
dissolution of toxic substance in low pH.
• Photochemical smog: Hydrocarbon (HC) + nitrogen oxides NOx in presence of
ultraviolet radiation
= Perxyacyl nitate (PAN) type of serious secondary air pollutants formed
National Ambient Air Quality Standard (NAAQS)-2009
It was notified on 16-11-2009 by government of India. Some of the important air
quality parameters are mentioned in the table

Pollutant parameter unit Averaging Concentration in ambient air

Industrial/residential Ecologically sensitive area

area

Sulfur dioxide µg/m 3 24 hourly 80 80

Nitrogen dioxide µg/m 3 24 hourly 80 80
Particulate PM10 µg/m 3 24 hourly 100 100
Particulate PM2.5 µg/m 3 24 hourly 60 60
Carbon monoxide µg/m 3 8 hourly 2000 2000
ozone µg/m 3 8 hourly 100 100
 Air pollution control

Gaseous pollutants
• Condensation involves removing heat from hot gas stream to reduce
the temperature so that some of the pollutant like ammonia get
condensed and so can be easily removed
• Absorption involves transfer of pollutant from gas stream to liquid
stream. Examples are removal of ammonia by water, hydrogen
sulphide by sodium hydroxide etc.
• Adsorption involves transfer of pollutant from gas stream to solid
surfaces having desirable surface properties.
• Flue gas desulphurization involves removal of SO2 from the flue gas
• NOx emission control involves various techniques for the removal of
NO and NO2 (NOx).
 Particulate pollution control
Pollution Removal mechanism Particle efficienc Design parameters
control size y
methods removal

Gravity settling Gravity >50 µ >50%

chamber -

Cyclone Centrifugal forces and >5 µ >85%

separator gravity -

Bag filter Interception, impaction < 0.1 µ >99% Air to cloth or filtering ratio
and diffusion 0.5 to 5 m/minute

Electrostatic Electrostatic forces of < 0.1 µ >99%

precipitator attraction
(ESP)
 Pollution control Equipment

• Gravity settling chamber

• Cyclone separators

• Fabric filters(Bag Filter)

• Electrostatic Precipitator

• Wet Collectors ( Scrubbers)

Electrostatic precipitator (ESP)

• An electrostatic precipitator is a filtration device that removes fine particles, like

dust and smoke, from a flowing gas using the force of an induced electrostatic
charge minimally impeding the flow of gases through the unit.
• The operation of electrostatic precipitators is fairly simple. The dirty flue gas
escaping through the smokestack is passed through two electrodes. The shape
these electrodes depends on the type of electrostatic precipitator used, but they
can be metal wires, bars, or plates inside a pipe or the smokestack itself.
• One of the electrodes is charged with a high negative voltage, and this plate
causes particulates inside the smoke to obtain a negative charge as they pass by
this electrode.
• Further along the pipe, the second electrode carries a similarly high positive
voltage. Based solely on the fact that opposite charges attract, the negatively
charged soot particles are pulled towards the positive electrode and stick to it.
• Occasionally these plates must be cleaned to remove the accumulated soot and
dispose of it into a hopper. The soot and ash collected from coal burning power
plants in this manner is referred to as fly ash.
 Numerical on ESP

Compute the plate area of ESP handling a flow of 3600 m3/min. If the
particulate velocity is taken as 0.15 m/s, and efficiency of ESP as 99 %

(ƞ) = 1- exp(- Aw/Q)

0.99 = 1- exp (0.15 x A/3600/60)

A = Area of plate =1842.1 m2

Baghouse filter
• One of the most efficient devices for removing suspended particulates is an assembly of fabric-
filter bags, commonly called a baghouse.
• A typical baghouse comprises an array of long, narrow bags—each about 25 cm (10 inches) in
diameter—that are suspended upside down in a large enclosure.
• Dust-laden air is blown upward through the bottom of the enclosure by fans. Particulates are
trapped inside the filter bags, while the clean air passes through the fabric and exits at the top of
the baghouse.
• A fabric filter dust collector can remove very nearly 100 percent of particles as small as 1 μm and a
significant fraction of particles as small as 0.01 μm.
 Numerical on bag filter

Q- A bag house is to be constructed using bags of 0.25 m diameter and 6

m long. It is to receive 15 m3/s of air. Assuming the filtration rate of 2.2
m/min. Determine the no bags required in the bag house.

Ans-Total filtration area required= gas flow rate/filtration rate= 15 x 60

m3/min/2.2 m/min= 409.1 m2

Area of one bag = pi x D x H= 3.14 x 0.25 x 6 =4.71 m2

No of bags required in bag house= 409.1/4.71 =86.8 that is 87 bags