This article talks about environmental issues, air pollution and controls. Global warming and other subjects are also included

1. 1. INTRODUCTION
Human population size has grown enormously over the last
hundred years which is exerting tremendous pressure on our
natural resources. Today, almost every aspect of modern living
contains potential health risks. Natural resources like air,
water, land, etc. are getting contaminated with toxic
substances or chemical additives. The adverse effects of
chemical pollutants in the environment are not limited to
ourselves, but pass on to future generations by way of genetic
mutations, birth defects, inherited diseases, and so on.
Environment is the physical, chemical, biological, cultural and
aesthetic surrounding of living organisms, which contributes to
the quality of their lives. Our environment is a complex and
dynamic system, in which all forms of life are inter-dependent
and inter-connected. The need of the hour is to check the
degradation and depletion of our precious natural resources
and pollution without halting the process of development.
2. WHAT IS POLLUTION?
Pollution is any undesirable change in physical, chemical or
biological characteristics of air, land, water or soil. Agents that
bring about such an undesirable change are called as
pollutants.
2.1 BASIC CAUSES OF POLLUTION The
basic cause of pollution is man himself. He has befouled
the clean land, water and air initially provided by nature.
This man made pollution is termed as anthropogenic
pollution (e.g., industrial pollution, agricultural pollution

2. etc.). This has been caused through overuse, misuse and
mismanagement of natural resources to fulfil human
needs. Several natural activities are also known to cause
natural pollution resulting from volcanic eruption, UV
radiation, soil erosion, dust storms, decomposition of
organic matter, forest fires, etc.
2.2 PROCEDURE FOR THE CONTROL OF POLLUTION
The control of pollution requires environmental
monitoring. This, in turn, needs
(i) Careful study of environmental characteristics,
(ii) Laying down environmental quality standards,
(iii) Periodic assessment of environmental
characteristics,
(iv) Noting the changes in the environment and finding
out their likely effect,
(v) Warning people in time of likelihood of pollution,
and
(vi) Planning strategies to tackle pollution such as
educating people about pollution hazards, enacting
environmental laws, legal action against offenders,
etc.
It is to be noted that in order to control environmental
pollution, the GOVERNMENT OF INDIA has passed the
“ENVIRONMENTAL (PROTECTION) ACT”, 1986 to
protect and improve the quality of our environment (air,
water and soil).
3. TYPES OF POLLUTION

3. Pollution is of following five main types:-
(i) Atmospheric or air pollution,
(ii) Hydrospheric or water pollution,
(iii) Lithospheric or land or soil pollution,
(iv) Radioactive pollution, and
(v) Noise or sound pollution.
4.AIR POLLUTION
An undesirable change in the physical, chemical or biological
aspects of air which makes it harmful for humans, other living
organisms and cultural assets is called air pollution.
4.1 CAUSES OF AIR POLLUTION
There are two main causes of air pollution:-
a. HUMAN ACTIVITIES, viz,
(i) Industrialization,
(ii) Automobile emission,
(iii) Overpopulation,
(iv) Deforestation,
(v) Nuclear explosion and explosives used in wars,
(vi) Fireworks on festivals,
(vii) Thermal power stations, etc.
b. NATURAL PHENOMENA such as
(i) Volcanic eruptions releasing harmful gases and
ashes,
(ii) Electric storms and solar flares which produce
harmful chemicals,
(iii) Forest fires,

4. (iv) Natural organic and inorganic decays releasing
methane, sulphur and other harmful substances,
(v) Dust storms,
(vi) Biological elements like pollen, spores, cysts,
bacteria and marsh gas.
4.2 AIR POLLUTANTS
Air pollutants are of three main kinds:-
(i) Gaseouspollutants
These are in gaseous state at ordinary temperatures
and pressures. They freely mix with air without
settling down. Some of them are:-
 Oxides of sulphur:- These include sulphur dioxide
(SO2) and sulphur trioxide (SO3).
SOURCES The oxides of sulphur are produced by
burning of fossil fuels (coal and oil) in industries,
thermal plants, residential premises and motor
vehicles, by smelting of non-ferrous metals (e.g.,
iron, copper, lead, zinc, nickel, etc.) and from
hydrogen sulphide (H2S) gas formed from natural
sources. They form about 18% of total air
pollutants.
EFFECT -The sulphur oxides are harmful to
buildings and clothing as well as to animals and
plants.
-They may cause respiratory diseases in man
(asthma, bronchitis, emphysema).

5. -High concentration of SO2 causes chlorosis, i.e.
change of chlorophyll into phaeophytin,
plasmolysis, membrane damage, metabolic
inhibition, reduced growth and yield, and death.
-SO2 and SO3 react with water to form sulphurous
acid (H2SO3) and sulphuric acid (H2SO4)
respectively. These acids cause irritation of eyes,
nose and throat. They also decrease the pH of
water, thus, adversely affecting aquatic life. The
highly corrosive H2SO4 attacks exposed metal
surfaces, such as steel rail track. They may
precipitate as rain or snow, producing acid rain or
acid precipitation which destroys crops and
vegetation.
-These also have mutagenic properties.
 HYDROGEN SULPHIDE:-
SOURCES It enters the atmosphere through the
decomposition of sewage wastes or organic
matter and from various industries.
EFFECT It is more poisonous than even carbon
monoxide and blackens lead paints and causes
corrosion of metals.
 OXIDES OF NITROGEN:- These include nitrogen
monoxide (NO) and nitrogen dioxide (NO2).
SOURCES The oxides of nitrogen are released by
automobiles and chemical industries as waste

6. gases and also by burning of materials. Nitrogen
dioxide is also formed from the atmospheric
nitrogen by electrical energy of lightning and by
natural ionising radiation. The nitrogen oxides
form about 10% of air pollutants.
EFFECT –Nitrogen monoxide , like CO, lowers the
O2 carrying capacity of the blood.
-NO2 forms, on contact with water vapour in air, a
highly corrosive nitric acid (HNO3). Hence, it
irritates the eyes, nose, bronchial tubes and
lungs. Its high concentration proves fatal. At a
concentration of 15 to 50 ppm, nitrogen oxides
are known to inflict injury to lungs, liver and
kidneys.
-Being a strong reducing agent, NO2 attacks
metals, textiles and other materials.
-Nitrogen oxides damage plants also, causing
defoliation and necrosis (pathological death of a
part of a tissue or an organ).
-Nitrogen oxides form peroxyacyl nitrate(PAN)
by reaction with hydrocarbons.
 OXIDES OF CARBON (INCLUDES CARBON
MONOXIDE AND CARBON DIOXIDE):-
SOURCES cigarette smoking, burning of fossil
fuels, released by living organisms during

7. respiration and formed by decay of organic
matter.
CARBON MONOXIDE (CO):- It is a colourless,
odourless, non-irritating but highly poisonous
gas. It is, however, not a persistent pollutant as it
gets converted into harmless compounds by
natural processes. It accounts for over 50% of the
total air pollutants.
EFFECT -If inhaled CO selectively combines with
haemoglobin and reduces the O2 carrying capacity
of haemoglobin. This can lead to giddiness,
laziness, exhaustion, reduced vision, nervous and
cardio-vascular disorders and even death.
CARBON DIOXIDE (CO2):-
EFFECT It causes nausea and headache. It ia a
major cause of “green house effect” and “global
warming”.
 HYDROCARBONS:- They are composed of
hydrogen and carbon, e.g., methane.
SOURCES
-Formed by incomplete combustion of fuels in
automobiles.
-Released by evaporation from petrol, organic
solvents and as components of natural gas.
-Formed by bacterial decomposition of organic
matter.

8. EFFECT –Many hydrocarbons are carcinogenic. For
instance, polynuclear aromatic hydrocarbons and
formaldehyde are carcinogenic.
-They cause irritation of eyes and mucous
membrane and bronchial constriction.
-They harm plants by causing senescence and
abscission.
-They give rise to secondary pollutants during
their interaction with oxides of nitrogen.
 PHOTOCHEMICAL OXIDANTS:- These include
peroxyacyl nitrate (PAN), ozone (O3) and
aldehydes.
SOURCES The photochemical oxidants are formed
by reaction of nitrogen oxides with the
hydrocarbons of the air in the presence of
sunlight.
N2 + O2 → 2NO (reaction inside engine)
2NO + O2 → 2NO2 (reaction in atmosphere)
Photochemical Reactions
NO2 → NO + [O] (in the presence of UV
radiations)
O2 + [O] → O3
NO + HC +O2 → NO2 + PAN
EFFECT All photochemicals are harmful.
 PAN:- It causes irritation of eyes and throat
and produces respiratory troubles (asthma,
bronchitis, emphysema, lung cancer ) in

9. man. It also affects the plants, particularly
the leafy vegetables such as spinach and
lettuce, causing silvering, glazing, banding,
bronzing and necrosis.
 OZONE :- The ozone formed in the
troposphere by photochemical reaction as a
result of human activities is harmful. At low
concentrations, it produces chest pain,
coughing and often eye irritation. High
concentrations can kill both animals and
plants. Ozone attacks textiles causing
decolouring and disintegration of clothes. It
damages rubber too, particularly automobile
tyres and rubber sealing around windows
and rubber insulation of electric wiring.
 SMOG:- It is a dark fog formed by
condensation of water vapours, dust and
smoke particles and various gaseous
pollutants such as NO2, SO2, H2S, etc. Smog
is generally categorised as classical smog
and photochemical smog.
EFFECT Smog causes toxic effect on man,
animals and plants and cracking of rubber. It
produces respiratory problems in humans. It
also reduces visibility leading to accidents.
-CLASSICAL SMOG/LONDON SMOG: It is
dark brown and opaque; formed by

10. condensation of water vapours with H2S and
SO2 over dust or smoke particles at low
temperature. It has reducing environment.
-PHOTOCHEMICAL SMOG/LOS ANGLES
SMOG: I t contains photochemical oxidants.
It is grey or yellowish brown, opaque smog
formed at high temperature over cities and
towns due to still air, emission of nitrogen
oxides and volatile hydrocarbons from
automobile exhausts and solar energy. It is
having oxidising environment.
 ALDEHYDES:- These compounds cause
irritation of gastrointestinal and respiratory
tracts.
 FLUORIDES:- These are compounds of fluorine.
SOURCES –industries which manufacture
aluminium, steel and phosphate fertilisers.
-small amounts are released during coal
combustion.
EFFECT Fluorides enter the leaves via stomata and
accumulate there. Animals that feed on such
plants acquire a disease called fluorosis (spotting
of teeth). Fluoride accumulation in fruit trees
reduces yield and in crops delays maturing. They
also attack glass paints and metal surface.
(ii) PARTICULATE POLLUTANTS
SOURCES

11. -industries
-automobiles
-operations such as blasting, drilling, crushing,
grinding, mixing, etc.
-BIOLOGICAL POLLUTANTS like pollen, spores, cysts
and bacteria, etc.
A brief description of some of them as follows:-
 DUSTS:- Fly ash and soot from burning of coal;
metal dust containing lead, chromium, nickel,
arsenic, cadmium, zinc and mercury from
metallurgical processes; asbestos fibres from
asbestos industry; stone particles from stone
grinders and cotton dust from textile mills are
added to the air
EFFECT The dusts cause respiratory trouble called
lung fibrosis or pneumoconiosis (G. pneumon=
lung, konis= dust, osis= condition). The inhaled
(a) asbestos fibres cause asbestosis that may lead
to lung cancer (b) cotton fibres cause byssinosis
(c) stone particles cause silicosis. Lung fibrosis
also occurs in flour mill workers and coal miners.
Combustion of petroleum in automobiles, burning
of coal and wastes, and pesticide spraying emit
particulate lead compounds. Lead affects central
nervous system. Symptoms of chronic lead
poisoning include headache, loss of appetite,
dizziness, insomnia, anaemia, weakness and

12. miscarriage. It also distorts red blood cells. Acute
lead poisoning causes stupor (dazed state), then
coma and finally death.
 MISTS:- The pesticides sprayed on crops may
remain in the air as liquid particles.
 AEROSOLS:- Aerosols are chemicals released into
the air with force as vapour. These include
chlorofluorocarbons(CFCs), nitrogen and sulphur
oxides, polychlorinated biphenyls (PCBs) and
tobacco smoke.
(a)CFCs
EFFECT CFC aerosol depletes the ozone layer in
the higher atmosphere. Thinning of the ozone
layer permits more of the harmful UV radiation
to reach the earth. UV rays cause sunburn,
blindness and inactivation of proteins, RNA,
DNA and plant pigments(also a mutagen).
(b)NITROGEN AND SULPHUR OXIDES
They have the same effect as CFCs.
(c)PCBs
These are produced by burning of plastic. They
reach human body via food chains.
EFFECT PCBs damage liver and central nervous
system, impair vision and change skin
pigmentation.
(d)TOBACCO SMOKE

13. It contains a hydrocarbon called benzpyrene.
Benzpyrene also results from coal and oil
combustion. It occurs in automobile exhausts
too. Some evaporates from tar.
EFFECT LUNG CANCER.
(e)POLLEN, SPORES, CYSTS AND BACTERIA
EFFECT When inhaled the pollen, spores and
cysts cause allergies and respiratory diseases,
commonly referred to as hay fever. The inhaled
microbes may cause diseases.
(iii) RADIOACTIVE POLLUTANTS
SOURCES Nuclear and war explosives
EFFECT They kill the tissues they enter.
4.3 CONTROL OF AIR POLLUTION
Three types of steps can be taken to control air pollution:
(a) SEPARATIONOF POLLUTANTSFROMHARMLESS GASES
This can be done by:
 Growing Trees
Certain plants (Phaseolus vulgaris, Coleus
blumeri, Ficus variegate) can fix carbon monoxide
and some plants (Pinus, Juniperus, Quercus,
Pyrus, Vitis) can metabolise nitrogen oxides.
Plantation of such species should be encouraged
along with other plants.
 Using sulphur and lead free good quality fuel

14.  Controlling particulate matter: Particulate matter
from the polluted air can be removed by fixing
various devices termed arrestors in the industries
and catalytic converters in the automobiles.
Arrestors are of various types- control
equipments such as gravity settling tanks or
porous filters,electrostatic precipitators, cyclonic
separators and trajectory separators installed in
factories can minimise air pollution. Catalytic
converters are the devices having expensive
metals(e.g., platinum, palladium and rhodium) as
the catalysts. Catalytic converters are fitted into
automobiles for reducing the emission of gases.
As the exhaust passes through the catalytic
converter, unburnt hydrocarbons are converted
into CO2 and H2O and carbon monoxide and nitric
oxide are changed to CO2 and N2 gas respectively.
Vehicles fitted with catalytic converters should be
run on unleaded petrol as leaded petrol would
inactivate the catalyst in the converters.
 Controlling gaseous pollutants: gaseous
pollutants can be removed by three methods:
 Combustion method: This method is used to
control oxidisable pollutants particularly in
petrochemical, fertilisers, paints and varnish
industries. In this method, emissions are burnt
at high temperature.

15.  Absorption method: This method employs dry
or wet scrubbers having packing material where
gaseous pollutants are absorbed. For instance,
calcium hydroxide or a bed of lime is used to
absorb SO2. Alternatively, a fine spray of water
dissolves nitrogen oxides, sulphur oxides and
ammonia.
 Adsorption technique: This method is
employed to remove toxic gases, vapour and
inflammable compounds from the polluted air
by using very fine solid particles (e.g., activated
charcoal). The electrostatic precipitators
remove smaller particles.
 The use of tall chimneys in factories can reduce
pollution of air at ground level.
 Industrial smoke should be filtered before
releasing it into the air to remove particulate
matter.
 Poisonous gases should be removed by passing
the fumes through water tower scrubber or spray
collector.
 Mining area should be afforested.
(b) AVOIDANCEOFPOLLUTANTS
This can be done by:
 Use of automobiles should be minimised.

16.  Conventional fuels (firewood, coal, oil) should be
replaced by electricity or natural gas (CNG). These
fuels do not emit SO3.
 Population growth, the main cause of pollution,
should be brought under control.
 Nuclear explosions and wars should be stopped.
 Effort should be made to get energy by means
which do not involve combustion. Such non-
combustible means of producing energy are
geothermal power, solar power, tidal power, wind
power and nuclear power. These means are
pollution free.
 Industries should be located away from the human
habitations.
 Use of high temperature incinerators can reduce
the production of ash.
 Pollution free fuels (alcohols, hydrogen, battery
power) should be developed for automobiles.
 Complete electrification of rail track will greatly
reduce air pollutants.
(c) CONVERSION OFPOLLUTANTS TO HARMLESS MATERIALS
This may be done by oxidation in the air or by
chemical neutralization of acids and bases.
NATURE’S WORK Where nature contributes to pollution by
activities like volcanic eruptions, it causes depollution also. High
winds disperse the pollutants. This reduces their concentration near
the source. Low temperature at higher altitudes causes vertical air

17. turbulence. This carries the pollutants high in the atmosphere.
Precipitation (rain, snow) cleans the air of pollutants.
5. ACID RAIN
The term “acid rain” was first coined by Robert August (1872).
Acidification of environment is a man- made phenomenon.
Acid rain refers to precipitation with a pH of less than 5. It is,
in fact, a mixture of H2SO4 and HNO3; the ratio of the two
acids varies dependingon the relative quantitiesof sulphur
oxides and nitrogen oxides present in the atmosphere. These
oxides are mainly produced by combustion of fossil fuels,
smelters, industries, power plants, automobile exhausts,
domestic fires, etc.
NOX are also produced in atmosphere through lightning. In
the atmosphere, SO2 and NOx are changedinto H2SO4 and
HNO3 respectively by combining with oxygen and water.
2SO2 + O2 → 2SO3
SO3 + H2O →H2SO4 (sulphuric acid)
2NO + [O] →N2O5
N2O5 + H2O → 2HNO3 ( nitric acid)
EFFECT
 Acid rain increases the acidity of the soil, thereby
affecting terrestrial flora and fauna. In plants, it
causes chlorosis, necrosis, defoliation, etc.
particularly at growing points.
 It also results in acidification of waterbodies,
thus, affecting aquatic life in most industrialized
countries. A pH of less than 5 kills plankton,
molluscs and most of fish in water bodies.
 It corrodes metals, marble, paintedsurfaces,
slate, stone, etc. For example, acids formed due

18. to pollution by industries(particularly Mathura
refinery) reacts with marble (CaCO3) of the Taj
Mahal corroding it. This phenomenon is termed
stone leprosy. Chemical reactions involvedare:
CaCO3 + H2SO4 → CaSO4 +CO2 + H2O
(marble)
CaCO3 + 2HNO3 → Ca(NO3)2 + CO2 + H2O
(marble)
 Nearly half of the natural forests have been
destroyed by acid rain in Europe and North-East
United States. Most acidic rain (pH of 1.5) has
occurred over West Virginia, USA.
6.GREEN HOUSE EFFECT AND GLOBAL WARMING
The term ‘greenhouse effect’ has been
derived from a phenomenon that occurs in a
greenhouse. Greenhouse looks like a small glass
house and is used for growing plants especially
during winter. In a greenhouse the glass panel lets
the light in, but does not allow heat to escape.
Therefore, the greenhouse warms up, very much like
inside a car that has been parked in the sun for a
few hours.
The greenhouse effect is a naturally
occurring phenomenon that is responsible for
heating of earth’s surface and atmosphere.
In order to understand the greenhouse
effect, it is necessary to know the fate of the
energy of sunlight that reaches the outermost
atmosphere. Clouds and gases reflect about one-
fourth of the incoming solar radiation, and absorb
some of it but almost half of incoming solar
radiation falls on earth’s surface heating it,
while a small proportion is reflected back. Earth’s
surface re-emits heat in the form of infrared

19. radiation but part of this does not escape into
space as atmospheric gases (e.g., CO2, methane,
etc.) absorb a major fraction of it. The relative
contribution of various greenhouse gases to total
global warming is given below:
The molecules of these gases radiate heat energy,
and a major part of which again comes to earth’s
surface, thus heating it up once again. This cycle is
repeated many a times. The above mentioned gases- CO2
and methane are commonly known as greenhouse gases
because they are responsible for the greenhouse effect.
Increase in the level of greenhouse gases has
led to considerable heating of earth leading to “global
warming”. During the past century, the temperature of
earth has increased by 0.6°C, most of it during the last
three decades. Scientists believe that this rise in
temperature is leading to deleterious changes in the
environment and resulting in odd changes (e.g. El Nino
effect), thus leading to increased melting of polar ice
caps and the Himalayan ice caps including other places.
60%20%
14%
6%
RELATIVE CONTRIBUTION OF VARIOUS
GREENHOUSE GASES TO TOTAL
GLOBAL WARMING
carbon dioxide methane CFCs nitrous oxide

20. Over many years, this will result in a rise in sea level
that can submerge many coastal areas. The total spectrum
of changes that global warming can bring about is a
subject that is still under active research.
The control measures include cutting down use
of fossil fuels, improving efficiency of energy usage,
reducing deforestation, planting trees and slowing down
the growth of human population, etc.
7. OZONE DEPLETION IN THE STRATOSPHERE
Ozone, if formed in the lower atmosphere (troposphere) harms
plants and animals. But, ozone found in the upper part of the
atmosphere (stratosphere) acts as a shield absorbing UV radiation
from the sun. UV rays are highly injurious to living organisms since
DNA and proteins of living organisms preferentially absorb UV rays,
and its high energy breaks the chemical bonds within these
molecules. The thickness of ozone in a column of air from the
ground to the top of the atmosphere is measured in terms of
“Dobson unit”.
Ozone gas is continuously formed by the action of UV rays on
molecular O2, and also degraded into molecular oxygen in the
stratosphere. There should be a balance between production and
degradation of ozone in the stratosphere. Of late, the balance has
been disrupted due to enhancement of ozone degradation by
chlorofluorocarbons (CFCs). CFCs find wide use as refrigerants. CFCs
discharged in the lower part of atmosphere move upward and reach
stratosphere. In stratosphere, UV rays act on them releasing Cl

21. atoms. Cl degrades ozone releasing molecular oxygen, with these
atoms acting merely as catalysts; Cl atoms are not consumed in the
reaction. Hence, whatever CFCs are added to the stratosphere, they
have permanent and continuing affects on Ozone levels. Although
ozone depletion is occurring widely in the stratosphere, the
depletion is particularly marked over the Antarctic region. This has
resulted in formation of a large area of thinned ozone layer,
commonly called as the ozone hole.
UV radiation of wavelengths shorter than UV-B, are almost
completely absorbed by Earth’s atmosphere, given that the ozone
layer is intact. But, UV-B damages DNA and mutation may occur. It
causes aging of skin, damage to skin cells and various types of skin
cancers. In human eye, cornea absorbs UV-B radiation, and a high
dose of UV-B causes inflammation of cornea, called snow blindness,
cataract, etc. Such exposure may permanently damage the cornea.
8.INTERNATIONAL INITIATIVES FOR MITIGATING
GLOBAL CHANGE
MONTREALPROTOCOLOn 16th September, 1987, twenty
seven industrialized countries signed an agreement to
limit the production and use of ozone depleting
substances (ODS), e.g., chlorofluorocarbons, phasing out
of ODS, and also to help the developing countries to
implement use of alternatives to CFCs. In may, 1989
MONTREAL PROTOCOL was ratified by 82 nations at
Helsinki (HELSINKI DECLARATION). 175 countries had
signed this protocol till march 2011.

22. EARTHSUMMITUNITED NATIONS CONFERENCE on
ENVIRONMENT and DEVELOPMENT was held in Rio-
de-Janerio, Brazil in 1992 popularly known as EARTH
SUMMIT. In this conference, recommendations of CCC
(CONVENTION on CLIMATE CHANGE) were signed by
154 nations. A general agreement was reached to
maintain emissions of greenhouse gases at 1990 levels.
KYOTOPROTOCOLA follow up international conference
was held in December, 1997 in Kyoto, Japan. In this
conference, an agreement was signed by different
countries to mitigate global environmental change by
taking appropriate measure to reduce emissions of
greenhouse gases at a level 5% below the 1990 level by
2008 A.D. to 2012 A.D.
9.CONCLUSIONS
Today, our environment is facing anthropological threats.
Burning issues of GLOBAL ENVIRONMENT CHANGE like
global warming and ozone depletion are threatening the
existence of living world. The need of the hour is to stabilise
the atmospheric concentrations of greenhouse gases which
is possible only when all the countries join hands in
lowering the global emissions of greenhouse gases from their
present levels.

23. THANK YOU