AIR Pollution

B.Sc. 3rd Year Chemistry General
Dr. Santarupa Thakurta
Department of Chemistry
It is the contamination of air by the discharge of
harmful substances.
Air pollution can cause health problems and it can
also damage the environment and property.
Modernisation and progress
have led to air getting more and
more polluted over the years.
Industries, vehicles, increase in
the population, and urbanization
are some of the major factors
responsible for air pollution.
1. Sulphur di oxide (SO2):
Source• Fossil fuel combustion at power plants (73%).
• Industrial processes such as extracting metal from ore.
• An erupting volcano can also emit high levels of SO2.
Harmful effectsCan lead to lung diseases.
2. Nitrogen oxide (NOx):
NOX represents composite atmospheric gases, nitric oxide NO
and nitrogen di oxide NO2.
SourceProduced from combustion of petrol, diesel from vehicles.
Harmful effectsCan make children susceptible to respiratory diseases in winters.
Carbon mono oxide (CO):
Source• Produced by the incomplete combustion of carbon-based fuels
including petrol, diesel, and wood.
• From the combustion of natural and synthetic products such as
C4H10 + 6O2  3 CO2 + CO + H2O
Harmful effectsCO can cause harmful health effects by reducing oxygen delivery
to the body's organs (like the heart and brain) and tissues.
At extremely high levels, CO can cause death.
Hb (Haemoglobin) + CO = [Hb.CO]
Suspended Particulate Matter (SPM):
• Complex mixture of extremely small particles and liquid droplets
• Range in size from a diameter of 0.00002  to 500 .
SourceParticle pollution is made up of a number of components,
including fly ash (containing Fe2O3, P4O10 etc.), polycyclic
aromatic hydrocarbons, and soil or dust particles.
Harmful effectsParticles that are 10 micrometers in diameter or smaller can
pass through the throat and nose and enter the lungs.
Once inhaled, these particles can affect the heart and lungs
and cause serious diseases like asthma, silicosis.
Photochemical smog was first described in the 1950s,
characterised by brown hazy fumes.
It is the chemical reaction of sunlight, nitrogen oxides and volatile
organic compounds in the atmosphere, which leaves airborne
particles and ground-level ozone.
NO2  NO + O,
O 2 + O  O3
3CH4 + 2O3  3 CH2=O + 3H2O
This noxious mixture of air pollutants can include the following:
 Nitrogen oxides
 Tropospheric ozone
 Formaldehyde, acrolene
 Peroxyacetyl nitrate (PNA)
Adverse effects:
All of these harsh chemicals are usually highly reactive and
It can inflame breathing passages, decrease the lungs'
working capacity, cause shortness of breath, pain when
inhaling deeply, wheezing, and coughing. It can cause eye
and nose irritation.
considered to be a problem
of modern industrialization. It
is more common in cities with
sunny, warm, dry climates
and a large number of motor
Acid rain occurs when the gases SO2 and NOx react in the
atmosphere with water, oxygen, and other chemicals to form
various acidic compounds.
The result is a mild solution of sulphuric acid and nitric acid.
2NO2 +O3 + H2O  2HNO3 + O2
2SO2 + O2  SO3
SO3 + H2O  H2SO4
Adverse effects:
 Both the lower pH and higher aluminium concentrations in
surface water that occur as a result of acid rain can cause damage
to fish and other aquatic animals.
 Soil biology & chemistry can be seriously damaged by acid rain.
Some microbes, unable to tolerate changes to low pH, are killed.
 The hydronium ions of acid rain also mobilize toxins, such as
aluminium, and leach away essential nutrients and minerals such
as magnesium.
 High altitude forests are especially vulnerable as they are often
surrounded by clouds and fog which are more acidic than rain.
Other plants and food crops can also be damaged.
Adverse effects:
Acid rain can damage buildings, historic monuments, and statues,
especially those made of rocks, such as limestone and marble,
that contain large amounts of calcium carbonate. Acids in the rain
react with the calcium compounds in the stones to create gypsum,
which then flakes off.
CaCO3 (s) + H2SO4 (aq)  CaSO4 (s) + CO2 (g) + H2O (l)
Acid rain also increases the corrosion rate of metals, in particular
iron, copper and bronze.
Stratospheric ozone is being destroyed by a group of
manufactured chemicals, containing chlorine and/or bromine.
List of Ozone Depleting Substances:
Chlorofluorocarbons (CFCs)
o Used as coolants in refrigerators, freezers and air conditioners in buildings an
cars manufactured before 1995.
o Found in industrial solvents, dry-cleaning agents and hospital sterilants.
o Also used in foam products — such as soft-foam padding (e.g. cushions
and mattresses) and rigid foam (e.g. home insulation).
Used in some fire extinguishers
Methyl Chloroform
Used mainly in industry — for vapour degreasing, some aerosols, cold
cleaning, adhesives and chemical processing.
Carbon Tetrachloride
Used in solvents and some fire extinguishers.
Stratospheric ozone filters out most of the sun's potentially
harmful shortwave ultraviolet (UV) radiation. If this ozone
becomes depleted, then more UV rays will reach the earth.
Exposure to higher amounts of UV radiation could have
serious impacts such as the following:
 More skin cancers, sunburns and premature aging of the
 Damage of several parts of the eye, including the lens,
cornea, retina and conjunctiva.
 Weakening of the human immune system.
 Plankton (tiny organisms in the surface layer of oceans) are
threatened by increased UV radiation.
 Wood, plastic, rubber, fabrics and many construction
materials are degraded.
Carbon di oxide and water vapour strongly absorb infra red
radiation (14000 – 250000 nm) and effectively block a large
fraction of earth’s emitted radiation. The radiation thus
absorbed by CO2 and H2O vapour is partly re-emitted to
earth’s surface. This results in an elevation of earth’s surface
Human activities, primarily
the burning of fossil fuels
and clearing of forests,
have intensified the natural
greenhouse effect, causing
global warming.
The effects of global warming are the environmental and
social changes caused (directly or indirectly) by human
emissions of greenhouse gases. Many impacts of climate
change have already been observed, including glacier retreat,
changes in the timing of seasonal events (e.g., earlier
flowering of plants), and changes in agricultural productivity.
Threats caused by rise of temperature:
 Hampering of world food production.
 Decrease of the biological productivity of ocean.
 The rise in sea levels would submerge coastal countries.
 The pollutants CO, NO and NO2 emitted from cars can be
converted to non-polluting CO2, H2O, NH3 and N2 through
catalytic converter using finely divided platinum as catalyst,
 Use of low-sulphur containing coal to minimise SO2 pollution.
 Use of alternative energy sources such as hydrothermal plants
and Nuclear power plants.
 For control of Particulate emissions electrostatic precipitator
and cyclone collector are employed.
 More plantation of trees to maintain balance in the atmospheric
CO2 level.

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