Air Pollution

❖ Source
❖ Types
❖ Effects on biosphere
and Meteorology
❖ Air Quality Control
 Air Pollution .

Air pollution is one of the most dangerous forms of

environmental pollution in current times. As a result of
natural and man-made activities, gases such as CO, SO2,
H2S, and oxides of nitrogen, mist particulates, and aerosol.
It occurs due to the presence of undesirable solid or gaseous
particles in the air in quantities that are harmful to human
health and environment.
The substances that are responsible for causing air pollution
are called air pollutants.
❑Causes of Air Pollution
-Industries
-Automobile and Domestic Fuels
-High Proportion of undesirable
❑Gases, such as sulphur dioxide and carbon dioxide
Sources of Air Pollution
Sources of air pollution can be classified into two category:
➢Man-made
➢Natural
I. Man-Made Sources
❖ Population explosion
❖ Burning of fossil fuels
❖ Vehicular discharge
❖ Rapid Industrilization
❖ Agricultural activities
❖ Modern warfare
❖ Smoking
Natural sources

• Forest Fire
• Volcanic eruption
• Dust storm
Types of Air Pollutants
• Primary Pollutants
A primary pollutant can be defined as a harmful chemical that directly enters the air as a result of either natural or man-made activities.
i. Oxides of carbon: Carbon monoxide: It is a colourless, odourless, non-irritating but very poisonous gas. It is a product by incomplete
combustion of fuel such as natural gas, coal or wood. Vehicular exhaust is a major source of carbon monoxide. iv. Carbon dioxide (CO2):
Its a greenhouse gas emitted from combustion. It is natural gas in the atmosphere.
ii. Nitrogen oxides: Especially nitrogen dioxide is emitted from high-temperature combustion. Nitrogen dioxide is the chemical compound
with the formula N02. It is responsible for photochemical smog, acid rain etc
iii. Hydrocarbon: VOCs are an important outdoor air pollutant. In this field they are often divided into the separate categories of methane
(CH4) and non-methane (NMVOCs). Methane is an extremely efficient greenhouse gas that contributes to enhanced global warming.
Other hydrocarbon VOCs are also significant greenhouse gases via their role in creating ozone and in prolonging the life of methane in
the atmosphere, although the effect varies depending on local air quality. Within the NMVOCs, the aromatic compounds benzene,
toluene and xylene are suspected carcinogens and may lead to leukaemia through prolonged exposure. 1, 3-butadiene is another
dangerous compound which is often associated with industrial uses.
iv. Sulphur oxides: Sulphur oxides (SOx): SO2 is produced by volcanoes and in various industrial processes. Since coal and petroleum often
contain sulphur compounds, their combustion generates sulphur dioxide. Further oxidation of SO2, usually in the presence of a catalyst
such as NO2, forms H2SO4, and thus acid rain. This is one of the causes for concern over the environmental impact of the use of these
fuels as power sources.
v. Particulate Matter: Particulates alternatively referred to as particulate matter (PM) or fine particles, are tiny particles of solid or liquid
suspended in a gas. In contrast, aerosol refers to particles and the gas together. Sources of particulate matter can be manmade or
natural. Some particulates occur naturally, originating from volcanoes, dust storms, forest and grassland fires, living vegetation, and sea
spray. Human activities, such as the burning of fossil fuels in vehicles, power plants and various industrial processes also generate
significant amounts of aerosols.
Secondary Pollutants
Secondary pollutants are formed by primary pollutants through their
reaction with normal atmospheric compounds

• Ozone (O3): Ozone is a secondary pollutant formed by photochemical reaction between primary
pollutants and natural atmospheric gas. Ozone affects the respiratory and nervous system.
• Sulfuric acid and nitric acid (component of acid rain): Acid rain forms when water in the air
combines with nitrogen oxides and sulfur dioxide (two types of pollutants) and then falls down the
surface of the Earth. It has many damaging effects on vegetation, lakes, fish, buildings and other
structures.
• Smog: When ultraviolet light from the sun reacts with nitrogen oxides in the atmosphere,
photochemical smog is produced.
• Particulate matter: Particulate matter or simply PM is a combination of solid particles and liquid
droplets that can be found in the air. PM contains hazardous elements such as arsenic, beryllium,
cadmium, chromium, lead, manganese, and nickel. PM causes significant health problems in humans
• Peroxyacyl nitrates (PANs): It is produced in the atmosphere when oxidized volatile organic
compounds combine with nitrogen oxide. It is a component of photochemical smog.
 Carbon monoxide:
(max permissible conc 40ppm)
• It is a colourless, odourless, non-irritating , most abundant but very poisonous gas.

• Source : It is a product by incomplete combustion of fuel such as natural gas, coal or wood. Vehicular exhaust is a major
source of carbon monoxide. Photochemical reactions in the atmosphere, biological oxidation by marine organisms, etc.

• Sink: There is continued increase in CO emission but amount of Co in atmosphere remains relatively constant suggesting that
a scavenging process or sink exist in atmosphere . Microorganism present in the soil converts significant amout of CO to CO2

• Effects: Carbon monoxide affects the respiratory activity as haemoglobin has more affinity for CO than for oxygen(about
250 times) . Thus, CO interferes with the blood’s ability to carry oxygen to different part of body . CO combines with HB and
thus reduces the oxygen-carrying capacity of blood.
• Hb+ O2 ->HBO2 -> Hb + O2 (Hb is an oxygen carrier through
• Hb+CO ⇆ HbCO which different body cells intake O2)
• This results in blurred vision, headache, unconsciousness and death due to asphyxiation (lack of oxygen).
• Asphyxia or suffocation may result if the oxygen concentration is reduced to below 19.5% by displacement
 Control of CO
• Control Methods:
1. Modification of Engine design: Engine design
should be modified to maintain right proportion
of oxygen in fuel air ratio for complete
combustion of fuel .
2. Fuel Modification: Fuel including natural gas
,methane and blends of lighter hydrocarbon is
recommended
3. Treatment of exhaust gases :two stage catalytic
converter preferred
I stage NOx ->N2 +NH3 {catalyst Pt,Pd and
Ru on ceramic material ,CO gas
II stage CO ->CO2 (Pt and Ru on
ceramic material)
 Nitrogen oxides (NOx): NO,NO2,N2O, N2O3,N2O5
• Source :
• Nitrogen dioxide is emitted from high temperature combustion, automobile exhausts, forest fires, electric generation plants, smelting plants,
industrial boilers, petroleum refineries, chemical industrie
• Natural Sources : During lightening discharge N2 and O2 in air combines to form NO. NO2 is formed by fixing of nitrogen from atmosphere as well as
from organic matter present in earth crust .
• N2 +O2 ->2NO
• Man Made Sources :
• N2 +O2 ⇆ 2NO (1200-1700oC) Combustion of fossil fuel
• 2NO+ O2 ->2NO2 (1100oC)
• NO + O3 → NO2 + O2 (reaction with ground level ozone)
• Sinks for NOx : NO and NO2 undergoes various photochemical and chemical reaction in the atmosphere ) lading to formation of HNO3. Thus all the
pollutants get precipitated in the form of nitrates during rainfall . Formation and destruction of NO2 as well as O3 is a cyclic process taking place in
atmosphere .
NO + O3 → NO2 + O2
NO2 + hv -> NO + O
O + O2 -> O3
In the presence of VOC , NOX reacts with water in presence of Oxygen resulting in the formation of HNO3.
4NO2 + O2 + 2 H2O(liq) → 4HNO3(aq)
2NO + O3 → N2O5 + O2
N2O5 + H2O -> 2HNO3
 NOx pollution
• N2O5 reacts rapidly with liquid water in aerosol particles This nitric acid contributes to acid rain or may deposit to
soil, where it makes nitrate, which is of use to growing plants.
• Nitrogen dioxide is an irritant gas, NOx mainly impacts on respiratory conditions causing inflammation of the
airways at high levels. Long term exposure can decrease lung function, increase the risk of respiratory conditions
and increases the response to allergens. NOx also contributes to the formation of fine particles (PM) and ground
level ozone, both of which are associated with adverse health effects.
• NOx gases react to form smog and acid rain as well as being central to the formation of fine particles (PM) and
ground level ozone, both of which are associated with adverse health effects.
Control of NOx :
1.Modification of Engine design : The burners are modified so that fuel air mixture burn slowly reducing
temperature and intensity of combustion.
2.Employing two stage combustion process (as discussed in CO)
3.I stage NOx ->N2 +NH3 {catalyst Pt,Pd and Ru on ceramic material ,CO gas
II stage CO->CO2 (Pt and Ru on ceramic material)
4.Scrubbing of flue gas with H2SO4
Oxides of Sulphur (SOx): SO2, SO3
• It is one of the most important contributor towards air pollution . SO2 is produced by volcanoes and in various
industrial processes. Since coal and petroleum often contain sulphur compounds, their combustion generates
sulphur dioxide.

• Sulphur oxides (SOx): SO2 and SO3

• Further oxidation of SO2, usually in the presence of a catalyst such as NO2, forms H2SO4, and thus acid rain.
This is one of the causes for concern over the environmental impact of the use of these fuels as power sources.
• Source :
• Natural sources :Volcanic eruption constitute 67% of SOx pollution. Distributes uniformly .
• Man made sources : Industries, burning of fossil fuels, forest fires, electric generation plants, Copper smelting
plants, industrial boilers, petroleum refineries . Found mostly in urban area.
• Cu2S + O2 -> 2Cu +SO2

• Sulphur dioxide is the product of burning of fossil fuel that contain sulphur:
• S + O2 → SO2
• A small amount of SO2 undergoes photolysis in air to form SO3
• 2SO2+ O2->SO3 + O2
Sox Pollution
• Sinks of SOx:
Formation of acid rain

• Effects of SOx:

•The highest concentrations of sulphur dioxide in the air are found around oil refineries,
chemical manufacturing industries, mineral ore processing plants and power stations.
•When sulfur dioxide combines with water and air, it forms sulfuric acid, which is the
main component of acid rain. Acid rain can cause deforestation , acidify waterways to
the detriment of aquatic life and corrode building materials and paints.
•Sulfur dioxide inhibits photosynthesis by disrupting the photosynthetic mechanism.
The opening of the stomata is promoted by sulfur dioxide, resulting in an excessive loss
of water.
•Sulfur dioxide affects the respiratory system, particularly lung function, and can irritate
the eyes. Sulfur dioxide irritates the respiratory tract and increases the risk of tract
infections. It causes coughing, mucus secretion and aggravates conditions such as
asthma and chronic bronchitis
ENVIRONMENT EFFECT OF AIR POLLUTION
• 1. SMOG :
• Term ‘smog’ is derived from the words ‘smoke’ and ‘fog’.
• Depending on the method of composition , two distinct types of smog are recognized:
1) Sulphurous smog or ‘London smog or Classic Smog
2) Photochemical smog /‘Los Angeles smog
A. Sulphurous smog/ (London smog)/Classic Smog : Reducing in nature , forms in winter month
• It is formed in morning hours of winter months when temperature is low
• Fog on the atmosphere condense on the carbon particle of the smoke to form SMOG.
• It results from the accumulation of smoke from coal burning, which has a high SO2 content and
humidity in air forms H2SO4 which deposits on particulates .
• inhibit the normal functioning of the lungs and can cause death.
SO2+O2 ->2SO3 (in presence of NO, soot or metal ion)
OR SO3+H2O ->H2SO3 SO3+H2O ->H2SO4
H2SO3 +1/2 O2 -> H2SO4
• London’s “Great Smog” of 1952 killed thousands and led the U.K. to enact clean air laws in subsequent
years.
Photochemical Smog
• Oxidising in nature , forms in summer months during afternoon, brown hazy fumes . Occurs most
prominently in urban areas that have large numbers of automobiles.
• Photochemical smog is therefore considered to be a problem of modern industrialization. Occurs in
cities with sunny, warm, dry climates and a large number of motor vehicles.
• In Delhi smog severity is often aggravated by stubble burning in neighboring agricultural areas. In
mega cities of the world it occurs by the phenomena of inversion that traps pollution close to the
ground. This type of smog requires neither smoke nor fog.
Un burnt hydrocarbon(VOC) + NOx+ sunlight ->O3 +PAN+ NO2 -> Photochemical Smog

•Photochemical smog proceeds through series of chemical reactions each involving

free radical mechanism :
N2 +O2 ⇆ 2NO (1200-1700oC) Combustion of fossil fuel
2NO+ O2 -> 2NO2 (1100oC)
NO2 +hv -> NO +O (In presence of sunlight , absorbs UVlight and dissociate NO2 )
O + O2 -> O3
NO + O3 -> NO2 + O2 (reaction with ground level ozone converts NO back to NO2 )
Cyclic reaction of formation of smog
• Reactive hydrocarbon from auto exhaust
interact with O3to form hydrocarbon free
radical RCH2’
• 2. RCH2’ reacts with O2 to form RCH2O2’free
radical
• 3. RCH2O2’ reacts with NO to produce NO2
and free radical RCH2O’
• 4. This new free radical interacts with O2 to
form stable aldehyde RCHO and hydroperoxy
radical HO2’
• 5. HO2 reacts with other molecule of NO to
give NO2 and OH’
• 6 OH’ is extremely reactive and rapidly reacts
with a stable hydrocarbon RCH3 to yield
H2Oand generate the hydrocarbon free radical
RCH2’ thereby completing the cycle . One
complete cycle yields two molecules of NO2
and one molecule of aldehyde RCHO and
regenerate free radical RCH2’ to start again .
Thus ,there is rapid build up of smog products .
 Phochemical smog

• 7.RCHO may initiate another route by interaction with HO’radical leading to

the formation of acyl radical RC’=O and further peroxy acy radical by
reaction with O2 and finally peroxy acyl nitrate PAN by reaction with NO2
• 8. O3, PAN and NOX constitutes photochemical smog . It is an eye irritant ,
causes respiratory irritation and retards plant growth .
• 9. Hydrocarbon level is high during early morning traffic rush hour and then
decreases during afternoon as it is consumed in smog formation reactions .
NO conc has peak value in early morning traffic and falls as NOx conc
increases .
• 10. It is usually toxic to humans and can cause severe sickness, a shortened
life span, or premature death
 Air pollution and Biosphere
• Atmospheric pollutants are mainly present to a great
extent in the troposphere and the lower stratosphere.
Depending on the extent of air pollution the atmosphere
can be divided into three layers.
• The first layer to 100m from the ground is highly polluted
in general and in urban and industrial area in particular.
Pollutants present in this layer absorbed by vegetation,
water surface, and buildings.
• The next layer is 100-2000m high, contains lesser
amounts of pollutants due to turbulent air currents,
drizzle, rain, and fog. They divert and dilute the
concentration of pollutants there.
• The third layer containing a large amount of water
vapour and clouds, extends up to the troposphere. Here
cloud water droplets dissolve some pollutants and bring
them back to the earth as rain.
• The secondary pollutants formed in the atmosphere by
the reaction of primary pollutants, water, oxygen, and UV
rays of the sun in the atmosphere affect the soil,
vegetation, crops, animals, and human beings.
 Effect of Air pollution on Meteorology
➢ It can be defined as the study of behaviour of atmospheric variations that determines the extent of air pollution.
➢ Factors like wind, whose speed and direction of flow directly determine the extent of dispersion and dilution of air
pollutants are called primary meteorology factor
➢ Precipitation, humidity, and solar radiation that control the dispersion of the pollutants indirectly are called secondary
pollutants.

• Wind speed and direction

When high pollutant concentrations occur at a monitoring station, wind data records can determine the general direction and area
of the emissions. Identifying the sources means planning to reduce the impacts on air quality can take place.
An instrument called an anemometer measures wind speed. At our monitoring stations, the type of anemometer we use is a sonic
anemometer.
A sonic anemometer operates on the principle that the speed of wind affects the time it takes for sound to travel from one point
to another. Sound travelling with the wind will take less time than sound travelling into the wind. By measuring sound wave
speeds in 2 different directions at the same time, sonic anemometers can measure both wind speed and direction.
• Temperature

Measuring temperature supports air quality assessment, air quality modeling, and forecasting activities. Temperature and

sunlight (solar radiation) play an important role in the chemical reactions that occur in the atmosphere to form

photochemical smog from other pollutants. Favourable conditions can lead to increased concentrations of smog. The most

common way of measuring temperature is to use a material with a resistance that changes with temperature, such as

platinum wire. A sensor measures this change and converts it into a temperature reading.

• Humidity

Like temperature and solar radiation, water vapour plays an important role in many thermal and photochemical reactions in

the atmosphere. As water molecules are small and highly polar, they can bind strongly to many substances. If attached to

particles suspended in the air they can significantly increase the amount of light scattered by the particles (measuring

visibility). If the water molecules attach to corrosive gases, such as sulfur dioxide, the gas will dissolve in the water and form

an acid solution that can damage health and property

Air Quality Index
The Central Pollution Control Board (CPCB) initiated its own National Ambient Air Quality Monitoring (NAAQM) program in
1985
Air Quality Control Technique
Following measures have been suggested to control air pollution- Common air pollution control technologies:
(i) Some gases, which are more soluble in a particular liquid than air, •Cyclones.
for example, ammonia in water, can be separated by dissolving in it •Scrubbers.
(ii) Particles larger than 50 mm are separated in gravity settling tanks. •Settling chambers
Using cyclone collectors or electrostatic precipitators separates fine • Filters.
particles. •Absorption.
(iii) The height of chimneys should be increased to the highest possible •Electrostatic precipitation.
level to reduce pollution at the ground level. •Adsorption
(iv) SO2 pollution can be controlled by extracting sulphur from the fuel •Combustion.
before use.
(v) Pollution control laws should be enforced strictly.
(vi) Trees should be planted on the roadside, riverbanks, parks and
open places as they keep the environment fresh.
Air Pollution Control Technique
Air pollution control devices control the amount of particulate matter escaping into the environment and devices
that control acidic gas emissions.
Electrostatic precipitator is a type of filter that uses static electricity to remove soot and ash from exhaust fumes
before they exit the smokestacks. Unburned particles of carbon in smoke are pulled out of the smoke by using
static electricity in the precipitators, leaving clean, hot air to escape the smokestacksIt is vit al to remove this
unreacted carbon from the smoke, as it can damage buildings and harm human health - especially respiratory
health.
Cyclone separator is a separation device that uses the principle of inertia to remove particulate matter from
flue gases. In these separators, dirty flue gas enters a chamber containing a vortex, similar to a tornado.
Because of the difference in inertia of gas particles and larger particulate matter, the gas particles move up the
cylinder while larger particles hit the inside wall and drop down. This separates the particulate matter from the
flue gas, leaving cleaned flue gas.
Air Pollution Control Technique
Fabric Filters : This method simply uses some sort of fabric like glass fibre - fabric bag would allow dust to
make its way through the fabric bag so that flue gasses must pass through it before exiting the
smokestacks. When the gas passes through, dust particles are trapped in the cloth.
Incineration
Incineration is used to convert VOC emissions into carbon dioxide and water through combustion. The
incineration generally takes place in a specialized piece of equipment known as an afterburner, which is built to
create the conditions necessary for complete combustion (such as sufficient burn time and a high
temperature).Additionally, the incinerated gas must be mixed to ensure complete combustion.
Scrubber are a type of system that is used to remove harmful materials from industrial exhaust gases before
they are released into the environment. These pollutants are generally gaseous, and when scrubbers are used
to specifically remove SOx it is referred to as flue gas desulfurization. There are two main types of
scrubbers, wet scrubbers and dry scrubbers. The main difference is in the type of material used to remove
the gases. By removing acidic gases from the exhaust before it is released into the sky, scrubbers help prevent