Environmental Science and Engineering – Study Material Unit II

UNIT – II : ENVIRONMENTAL POLLUTION

PART – A

1. Define Environmental pollution.

Environmental pollution is defined as any undesirable change in the physical, chemical or
biological characteristics of any component such as air, water, soil etc., which can cause harmful
effects on living organisms.

2. What are pollutants?

The materials or substances which cause pollution to the environment. It may be solid, liquid or
gases.
Examples: solid pollutants - metal, plastics, human waste and animal waste
Liquid pollutants - oil spill, pesticides and liquid detergents
Gaseous pollutants – sulphur dioxide, carbon monoxide, hydrocarbons, nitrogen oxides

3. Suggest three points as an individual responsibility in the prevention of pollution.

i)Plant trees ii) Avoid the usage of polythene carry bags iii) Use public transport rather than using
own transport such as two wheeler or four wheeler iv) Use ecofriendly products

4. Give a comprehensive definition for air pollution. / What is air pollution?

Air pollution is defined as, ‘the presence of unwanted gaseous substances, particulate matter,
radioactive substances, dust, smoke, mist, odour in the atmosphere which can cause dangerous effect
on human beings and other living organisms.

5. What are the causes of air pollution?

Air pollution is caused by natural and man made sources.
Natural sources:
Volcanic eruption, Forest fires, Biological decay, Sea salt spray, Pollen grains of flowers
Man made sources:
Thermal power plants (fly ash, SO2), industrial units, vehicle emission - (CO-77%,
HC-14%, NOx-8%), fossil fuel burning, Agricultural activities.

6. Differentiate between primary and secondary air pollutants with examples.

S.No. Primary air pollutants Secondary air pollutants
They are formed in the atmosphere by
They are emitted directly from
1 chemical interaction between primary
the sources
pollutants and atmospheric constituents.
They are found in the
These are not in their original form of
2 atmosphere in their original form
emittance
of emittance
Ex: oxides of nitrogen & Ozone, SO3, peroxyacylnitrate (PAN)
3
sulphur, smoke, dust, fumes etc. etc.
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7. What are particulate matter?

The pollutants which are in the form of suspended droplets, minute solid particles or mixtures of
two are generally referred to as particulates. Its size vary from 0.1 µm to 100 µm
Eg: Aerosols, Dust, Smoke, Fog, Smog etc.,

8. What is photochemical smog? How is it formed? Mention its causes.

It is the brownish smoke appeared in large cities with large amounts of automobile traffic in the
presence of sunlight.
It is formed by the combination of NO, NO2, CO, CO2, SO2, H2, and un-burnt hydrocarbon
particles.
Causes:
It is mainly due to chemical reaction among nitrogen oxides and hydrocarbon by sunlight.

9. List the sources of toxic pollutants in water.

S.No. Toxic pollutants Sources
Compounds of toxic metals such as Pb,
1 Industrial effluents, surface run off
As and Se
Nuclear power plants, mining and
2 Radioactive isotopes of I, Rn, U, Ce, Th processing of Uranium, nuclear
weapon production.
3 Pesticides Agricultural field
Zinc smelters and drainage water
4 Cadmium, Mercury, Lead
from mines.

10. Define the terms (a) BOD (b) COD, (c) toxicity.
BOD (Biological Oxygen Demand) is the amount of oxygen required for the biological
decomposition of organic matter present in the water.
COD (Chemical Oxygen Demand) is the amount of oxygen required for chemical oxidation of
organic matter using some oxidizing agents like K2Cr2O7 or KMnO4.
Toxicity is the degree to which a substance can damage an organism (human or animal). Toxicity
of a substance depends on dosage, ability to be absorbed, excretion and distribution within the body.
11. State the causes of soil pollution.
i) Industrial waste ii) Urban waste iii) Chemical and metallic pollutants iv) Biological agents
v) Radioactive pollutants vi) Agricultural practices
12. What is marine pollution?
Contamination of sea water due to discharge of industrial waste, spilling of oil from oil well,
dumping of nuclear waste and other wastage etc., which results in harmful to marine organisms
and also humans is known as marine pollution
13. What are the major sources of marine pollution? Mention its adverse effect on environment.
(Give two reasons for marine pollution)
S.No. Sources Effects
1 Dumping the wastes damage in birds as thinning of eggshell and tissue damage
(Discharging industrial of egg, damage to coral reefs.
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wastes)
2 Oil Spilling from oil Damage to marine fauna and flora, retard the rate of oxygen
well uptake by water.

14. List the sources of Marine Pollution.

i) Industrial wastes include heavy metals, radioactive nucleides, inorganic chemicals.
ii) Leakage of oil tankers and pipelines in ocean
iii) Oil tanker and ship accident
iv) Garbage such as plastics, ropes, tin cans etc., are dumped into the sea.
i) Domestic sewage and agricultural waste.
15. What are green house gases? Give examples
Greenhouse gas is a gas that both absorbs and emits radiation (heat) in the IR range.
The four major greenhouse gases, which cause adverse effects, are
1. CO2.
2. CH4.
3. Nitrous Oxide (N2O).
4. Chlorofluoro carbons (CFCs).

16 . What are the preventive measures of global warming?

 CO2 emission can be cut by reducing the use of fossil fuels.
 Implement energy conservation measures.
 Utilize renewable resources such as wind, solar and hydropower.
 Plant more trees.
 Adopt sustainable agriculture.
 Stabilize population growth.

17. Define Acid rain?

Because of SO2 and NO2 gases as pollutants in the atmosphere, the pH of the rain
water is further lowered. This type of precipitation of water is called acid rain (or) acid
deposition.
Sulfur trioxide reacts with water to form Sulfuric acid
SO3 (g) + H20 (l) → H2SO4 (aq)
Nitrogen dioxide reacts with water to form nitrous acid and nitric acid
2NO2 + H2O → HNO2 + HNO3
18. What is ozone layer depletion?
The process of creation of hole by greenhouse gases like CFC, SO 2 & NO in the ozone layer
in the stratosphere is called ozone layer depletion or ozone hole.
19. What are ozone depleting substances?
Ozone depleting substances include:
 Chlorofluorocarbons (CFCs) – released from refrigerants, propellants and cleaning solvents,
 Carbon tetrachloride (CCl4) - dry-cleaning solvent, as a refrigerant, and as a component in fire
extinguishers.
 Bromofluorocarbons (BFCs) – Fire extinguishers
 Hydrochlorofluorocarbons (HCFCs) - CFC substitutes.

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PART – B

1. Define air pollution. What are the sources of air pollutants? Explain the approach to control of
air pollution. Identify the sources of the following air pollutants and their effects on human
health: Carbon Monoxide, Nitrogen Oxide, Sulphur Oxide and particulate matter.
2. What is a particulate matter? How is it controlled by using equipment?
3. Explain the causes, effects and control measures of water pollution. Discuss the measures that
should be taken to de-pollute our waterways.
4. What is soil pollution? Explain the causes, effects and control of soil pollution. / What are the
causes and control measures for air pollution and soil pollution?
5. Discuss the causes, effects and control of marine pollution. /Give an account on
the causes and effects of marine pollution. Add a note on the control measures.
6. Discuss the role of an individual in preventing pollution.
7. Illustrate in detail about Green House Effects and Global Warming with neat sketch. /
Distinguish between natural and enhanced green house effect. List the principal green house
gases. Outline the effects of global warming.
8. Discuss the causes and effects of the following i) Acid rain ii) climate change
9. How is ozone formed? Write the causes, effects of ozone layer depletion.

PART - B: TOPICS

1. Air Pollution
The presence of unwanted gaseous substances, particulate matter, radioactive substances,
dust, smoke, odour in the atmosphere which can cause dangerous effect on human beings and other
living organisms.
Sources: power plants, mining activities,

Pollutants Sources Effects on Humans Effects on Environmental

Cigarette smoking, Reacts with
Carbon monoxide incomplete combustion hemoglobin in red Increases global
(CO) of fuels blood cells causes temperature
headache and anaemia
Damages trees, soils &
Nitrogen- di- oxide Fossil fuel burning in aquatic life in lakes, HNO3
Lung irritation and
(NO2) motor vehicles and
damage corrodes statues, buildings,
power industrial plant
monuments
Power plants and Damages trees, soils &
Sulphur-di- oxide Breathing problem
industrial plants aquatic life in lakes.
Suspended particulate Burning coal in power Nose and throat Damages trees, soils &
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matter and industrial plants, irritation, lung damage, aquatic life in lakes.
agriculture,construction bronchitis, asthma etc
etc.,

Photochemical Irritation of eyes, nose

Ozone Moderate the climate
reactions and throat
Chemical reaction Breathing problem,
among nitrogen oxide cough, eye, nose and Damages trees, soils and
Photochemical smog
and hydrocarbon by throat irritation, heart can reduces visibility.
sunlight diseases
Agriculture, decay of
Damages plants at low
Hydrocarbons plants, Carcinogenic
concentration.
burning of wet logs.
Paints, Smelters, lead Brain and nervous
Lead storage battery, leaded system , digestive Can harm wild life
petrol problem, cancer
Perforation of nasal
septum, gastrointestinal
Paints, Smelters,
Chromium ulcer, central nervous -----
chromium plating
system disease &
Cancer

General effects of Air Pollution on Human Health:

 Irritation of the respiratory tract.
 Irritation of eye, nose and throat
 Lead particulates (from automobile exhaust) cause lead poisoning resulting in convulsion,coma, and
even death.
 Cadmium particulates (through cigarette smoking) cause cardio vascular disease, kidney and liver
damage.
General effects of Air Pollution on Environment

Effects on Plants

 SO2 gas decreases the chlorophyll content and cause chlorosis

 NO2 causes permanent leaf fall and suppressed growth of plants resulting in reduced yields of crop
plants.
 PAN (Peroxyacylnitrate) damages leaf vegetables and cause premature fall.
 Ozone causes ‘necrosis’ (dead area on leaf) and damages the leaves.
Effects on Materials:
 Corrosion, Abrasion, and Chemical attack on surfaces
 Gases like SO2, NO2 and acid rain damage the building materials.
 Metal undergoes corrosion by acidic gases easily.
 Tensile strength of textiles is reduced by gases like O3 , SO2 , NO2 etc.,

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Control of air pollution

 Using non conventional energy

 Using bio filters
 Reducing vehicle exhausts
 Using less polluting fuels
 Using mass transport
 Removal of NOX from vehicle
 The emission from automobile is minimized by cleaning the exhaust gases by using suitable
catalysts like MnO2, CuO, Fe2O3.
 The industrial areas should be located at a certain distance from residential area.
 Plant more trees to reduce the concentration of CO 2 gas in atmosphere.
 The smoke particles can be removed by means of electrostatic precipitators.
MW
 Microwaves can be used to split toxic gase. ( H2S H2 + S).
 The smoke particles can be removed by means of electrostatic precipitators.
 For removing dust gas filters, cyclone seperators can be used.

2. Particulate Matter

The pollutants which are in the form of suspended droplets, minute solid particles or mixtures
of two are generally referred to as particulates. Its size vary from 0.1 µm to 100 µm
Control measures
i) By using Cyclone collector:
 In this method, particulate in gases are allowed to flow into a very tight circular spiral fitted chamber.
 It consists of a cylinder with an inverted cone attached at the bottom.
 The dirty gas with particles is allowed to enter at the top of the cylinder and spins forming a vortex. Due to the
centrifugal force of vortex the solid particles strike the wall of the cylinder and the particles fall in the hopper,
which is removed periodically.Due to centrifugal force, the particulates are settled down due to gravity from
where they are removed.
 They are collected in the bottom and discarded periodically.
ii) By using wet scrubber:
 Dirty gases are passed through water in the chamber.
 Particles are made wet and are removed from the gas stream which leaves from the top of the scrubber.
 Wet scrubber is very efficient for removing the particulates.
 The scrubber is very useful for removal of toxic and acidic gases.
iii) By using Cottrell electrostatic precipitator:
 Smoke contains negatively charged carbon particles in air.
 It is sent through a chamber maintaining at a very high potential of +30,000 V or more.
 Under this strong influence of electric field, the negatively charged particles are separated at the bottom.
 The hot dust free gases go out through the outlet chimney.

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Fig . 1 CYCLONE SEPARATOR 2. WET SCRUBBER 3. COTTRELL

PRECIPITATOR

3. Water Pollution

Contamination of fresh water by discharging the industrial effluents and other organic wastes
which alter the physical, chemical and biological properties of water and also cause harmful effects
on humans and aquatic life is known as water pollution.
Sources: Industrial wastes, domestic wastes, agricultural wastes, toxic elements

S.No Name of the Pollutant Example Source Effect

1. Infectious agents bacteria, virus Human and Various diseases.
animal waste.
2. Oxygen demanding Organic wastages Sewage, effluents Aquatic life affected.
wastages
3. Inorganic chemicals Pb,Se,Cu,acids Surface run off, Cancer, liver, kidney
effluents affected.

4. Plant nutrients Nitrate,Phophate Sewage, surface Eutrophication

run off
5. Organic chemicals Oil,petrol,diesel Surface run off, Nervous system affected,
effluents cancer, aquatic life
affected
6. Sediment Soil, silt Soil erosion Reduced Photo synthesis,
aquatic life affected
7. Radioactive materilas Uranium, Thorium Mining , nuclear Genetic mutation, birth
and Radon power plant defects, certain cancers.
8. Heat ( Thermal Excessive Heat Industries, Power Lower the DO level
Pollution) plant

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Control measures of water pollution

 Plant more trees
 All domestic and municipal sewage or effluent be drained in water bodies only after treatment.
 State and Central Governments should take responsibility to reduce water pollution.
 Use of pesticide, fungicide should be limited and quality pesticides should be used.
 Chemicals such as potassium permanganate should be spread regularly to control pathogenic
microorganism in water.
 The toxic chemicals like P. Mg, Na and NH3 may be removed by absorption, adsorption, ion –
exchangers and electro-dialysis.
 Discharging the wastages in water sources should be avoided.
 The industrial plants should be based on recycling operations.
 Public awareness regarding adverse effects of water pollution is must.
 The possible reuse or recycle of treated sewage effluents and industrial waste should be emphasized
and encouraged.

4. Soil Pollution
Soil pollution is defined as “the contamination of soil by human and natural activities
which may cause harmful effects on living beings.”
Sources : i) Industrial waste ii) Urban waste iii) Chemical and metallic pollutants iv) Biological
agents v) Radioactive pollutants vi) Agricultural practices

Types Sources Effect

pulp and paper mills, chemical
Industrial waste
industries, oil refineries, fertilizers, affects living organisms
pesticides.
Urban waste Commercial and domestic waste. ----
Agro-technology, fertilizers, affects living organisms.
Agricultural practices
pesticides, herbicides.
Explosion of nuclear dust Harmful to plants, aquatic life
Radioactive pollutants
radioactive wastes. and human beings.
Biological agent Humans and animals, birds excreta Damage to plants.
General effects on Soil Pollution
 Hazardous chemical entered into the food chain from soil, causes disruption of biochemical process.
 Soil becomes infertile because of water logging and salinity.
 Toxic chemicals affect plant growth and animal life.
 Excess usage of Na, K, Mg, etc., are affecting the growth of plants.
 Presence of special ions, change of pH of the soil make it unfit for irrigation.
Control Measures of Soil Pollution
 The waste from various industries should be properly treated before dumping into the soil and
water.

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 Use of bio-fertilizers should be promoted instead of chemical fertilizers.

 Use of toxic and non-biodegradable materials should be discouraged.
 Education programmes regarding soil pollution and prevention measures should
be promoted.
 There should be strict enforcement of environment protection law.
 Recycling and reuse of solid waste generated from various sources should be done.
 To minimize soil pollution, the wastes such as paper, plastics, metals, petroleum products and
industrial effluents etc., should be recycled and reused.
 Reducing deforestation and substituting chemical manures by animal wastes would also help
to arrest soil erosion in the long term. Maintaining soil productivity is vital and essential for
sustainable agriculture.

5. Marine Pollution
Contamination of sea water due to discharge of industrial waste, spilling of oil from oil
well, dumping of nuclear waste and other wastage etc., which results in harmful to marine
organisms and also human is known as marine pollution

Sources: Toxic chemicals, radioactive materials, agricultural wastes, oil spill, thermal power
plant

Effects of Marine Pollution

 The presence of heavy metals and organic pollutants cause more damage in birds as thinning
of eggshell and tissue damage of egg.
 Oil pollution cause damage to marine fauna and flora including algae, fish, birds. About
50,000 to 2,50,000 birds are killed every year by oil.
 Oil films are able to retard significantly the rate of oxygen uptake by water.
 Hydrocarbons and benzpyrene accumulate in food chain consumption of fish by man cause
cancer. Detergents used to clean up the spill are also harmful to marine life.
Control Measures of Marine Pollution
 Toxic pollutants from industries and sewage treatment plants should not be discharged in
coastal waters.
 Run off from non-point sources should be prevented to reach coastal areas.
 Dumping of toxic, hazardous wastes and sewage sludge should be banned.
 Developmental activities on coastal areas should be minimized.
 Oil and grease from service stations should be processed for reuse.
 Ecologically sensitive coastal areas should be protected by not allowing drilling.
Methods of Removal of Oil spillage:
1. Physical Methods:
i) Skimming the oil off the surface with a suction device appears to be the simplest method.
ii) The floating oil can be absorbed using a suitable absorbing material like PU-
Polyurethane foam.
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iii) Chemicals can be used to coagulate the oil.

2. Chemical Methods:
i) Dispersion ii) Emulsification iii) Using chemical additives
Protective measures:
i. Municipal and industrial waste should be treated before being allowed to join the sea.
ii. Coastal waste should be periodically analyzed for detecting pollution levels.
iii. Soil erosion in the coastal land should be arrested by suitable control techniques.
iv. Recreational beaches should be maintained to meet hygienic and aesthetic standard.

6. Role of an Individual in Preventing Pollution.

 Plant More Trees.
 Help more in pollution prevention than pollution control.
 Use of water, energy and other resources efficiently.
 Purchase recyclable, recycled and environmentally safe products.
 Use CFC free refrigerators
 Use natural gas than coal.
 Reduce deforestation.
 Increase use of renewable resources.
 Use less polluted substitutes for harmful cleaning agents, paints and other products.
 Reduce garbage by recycling and reuse.
 Use organic manure instead of commercial inorganic fertilizers.
 Use of eco-friendly products.
 Reduce garbage by recycling and reuse.
 Do not put pesticides, paints, solvents, oils or other harmful chemicals into the drain or ground
water.
 Reduce the use of fossil fuel.
7. Green House Effect and Global warming
The phenomenon whereby the earth's atmosphere traps solar radiation, caused by the presence
of gases such as carbon dioxide, water vapor, and methane in the atmosphere that allow incoming
sunlight to pass through but absorb heat radiated back from the earth's surface is called green house
effect
It is similar to the warming effect observed in the horticultural greenhouse made of glass.

Definition
The greenhouse effect may be defined as, “the progressive warming up of the earth’s surface
due to blanketing effect of man-made CO2 in the atmosphere.”
The greenhouse effect may be classified Natural Greenhouse effect and Enhanced Greenhouse effect
S.No Natural Green House Effect Enhanced Green House Effect
1. Green house has to do with plants Global warming has to do with atmosphere
2. It occurs naturally It is due to human activities
3. Green house effect can be controlled Global warming cannot be controlled

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Major Green house Gases and their sources

Green house Human Sources Average Time in the Relative warming

gases Troposphere potential (compared
to CO2)

Fossil fuel burning,

Carbon dioxide especially coal, 50-120 years 1
(CO2) deforestation, and plant
burning.
Rice paddies, guts of cattle
and termites, landfills, coal
Methane (CH4) production, coal seams, and 12-18 years 23
natural gas leaks from oil
and gas production.

Nitrous Oxide Fossil fuel burning,

fertilizers, live-stock wastes. 114-120 years 296
(N2O)

Chlorofluoro Air conditioners,

refrigerators, plastic foams. 1-20 years 900-8,300
carbons (CFCs)

Hydrochloro - Air conditioners,

9-390 470-2000
Fluorocarbons refrigerators, plastic foams.
(HCFCs)
Air conditioners,
HFCs 15-390 130-12700
refrigerators, plastic foams.

Carbon tetra
Cleaning solvent 42 1400
chloride (CCl4)

Causes of Green House effect (or) Green House Gases

Green house gas (GHC) is a gas that both absorbs and emits radiation (heat) in the IR range.
The four major green house gases, which causes adverse effects are
i. CO2 ii. CH4 iii. Nitrous Oxide (N2O) iv. Chlorofluorocarbons (CFCs)

Green House Effect

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Global Warming
The increased inputs of CO2 and other green house gases into the atmosphere from human activities
will enhance the earth’s natural green house effect of raising the average global temperature of the
atmosphere near the earth’s surface. This enhanced green house effect is called global warming.

Effect on Global Warming

1. Effect on sea level: As a result of glacier melting and thermal expansion of the ocean, a 20 cm rise is
expected in sea level by 2030.
2. Effect on agriculture and forestry: High CO2 level in the atmosphere have long-term negative
effects on crop production and forest growth. More grain belts would become less productive. As
climate pattern shifts, rain fall is reduced and soils are dried out resulting in major drought.
3. Effect on water resources: Global rainfall patterns will change and the water management strategies
of different regions will need to adapt to these changes. Drought and floods will become more
common, while rising temperature will increase domestic water demand.
4. Effect on terrestrial ecosystems: Many plant and animal species will have problems of adapting.
This will influence the mix of species at different locations. Many will be at risk from extinction,
whereas more tolerant varieties will thrive.
5. Effect on human health: As the earth becomes warmer, the floods and droughts become more
frequent. There would be increase in waterborne diseases carried by mosquitoes and other disease
vectors. The climate change might cause some ecosystem to exceed critical thresholds and result in
irreversible decline.

Measures to check Global Warming (Preventive Measures)

1. CO2 emission can be cut by reducing the use of fossil fuels.
2. Implement energy conservation measures.
3. Utilize renewable resources such as wind, solar and hydropower.
4. Plant more trees.
5. Shift from coal to natural gas.
6. Adopt sustainable agriculture.
7. Stabilize population growth.
8. Efficiently remove CO2 from smoke stacks.
9. Remove atmospheric CO2 by utilizing photosynthetic.

8. Climate Change:

Climate is the average weather of an area. It is the general weather conditions, seasonal variations
and extremes of weather in region. Such conditions which average over a long period at least 30 years is
called climate.
Causes of Climate Change
 Uneven distribution of rainfall
 Ocean current
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 Earth orbital changes

 Solar variations gases in the atmosphere (Global warming)
 Depletion of ozone layer
 Presence of Green house
Effect of climate change

 Disturbs agriculture and lead to migration of animals including humans.

 Affects the hydrological cycle.
 Global pattern of wind and ocean currents also get disturbed by climate.

9.Acid Rain
Acid rain, or more accurately acid precipitation, is the term used for describing rainfall with a pH
level lower than 5.6.

Formation of Acid Rain

As rainwater falls through the atmosphere, particles suspended in the air are dissolved in it.

These substances are generally dust, pollen grains and carbon dioxide. CO 2 combines with water to
form carbonic acid (H2CO3).
H2O(l) + CO2(g) →H2CO3(aq)

Sulfuric acid and nitric acid are the main acids present in acid rain.
Sulfuric acid is formed as follows:

 Sulfur released into the atmosphere combines with atmospheric oxygen to form sulfur dioxide (SO 2)
 Sulfur dioxide reacts with atmospheric water to form sulfurous acid
SO2 (g) + H2O (l) → H2SO3 (aq)
 Sulfur dioxide gradually oxidizes to form sulfur trioxide
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2SO2 (g) + O2 (g) → 2SO3 (g)

 Sulfur trioxide reacts with water to form Sulfuric acid
SO3 (g) + H2O (l) → H2SO4 (aq)

Nitrogen dioxide(NO2) is formed as follows:

 Nitrogen combines with atmospheric oxygen to form nitrogen dioxide (NO2).

 Nitrogen dioxide reacts with water to form nitrous acid and nitric acid
2NO2 + H2O → HNO2 + HNO3

Effects of acid rain

The following are the adverse effects of acid rain on living organisms and infrastructure
Buildings and Monuments:
 Acid rain causes severe damage to buildings and marble statues.
 Acid rain has partly eroded many world-famous monuments and buildings like the Taj Mahal in
India, St. Paul's Cathedral in London, and the Statue of Liberty in New York.
Acid rain can destroy stained glass windows in churches, bridges made of steel, and railway tracks.
 It corrodes metal,
 ruins the paint color,
 It forms a crust on glass surfaces.

Trees and Plants:

 Acid rain washes away important minerals from leaves and soil.
 Acid rain also blocks the small pores on the leaves' surface, through which they take in carbon
dioxide
Soil:
 Soil contains many harmful minerals such as mercury and aluminum. Acid rain reacts with these
chemicals and forms their compounds.
 Such compounds which are extremely harmful to living forms ultimately affect the entire food chain.
 These chemicals not only harm the flora, but also the animals that feed on them.

Water Bodies:
 Harmful substances like aluminum, lead and mercury, are washed away from the soil to neighboring
water resources by the acid rain, thus resulting in water pollution.
 This also results in depletion of oxygen levels in water which affects aquatic animals.

Human Health:
 Acid rain is harmful to human health.

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 Acids are very small and fine particles. They are normally in a liquid state. When they are present in
the atmosphere, they easily enter the lungs while breathing.
 It may even lead to cancer.
Control of Acid Rain
 Emission of SO2 and NO2 from industries and power plants should be reduced by using
pollution control equipments.
 Liming of lakes and soils should be done to correct the adverse effects of acid rain.
 A coating of protective layer of inert polymer should be given in the interior of water pipes for
drinking water.

9. Ozone Layer Depletion

Ozone is present in the stratosphere. The stratosphere reaches 30 miles above the Earth, and at the
very top it contains ozone. The sun’s rays are absorbed by the ozone in the stratosphere and thus do not
reach the Earth.
Measurement of Ozone : The most common stratospheric ozone measurement unit is the Dobson Unit
(DU). The Dobson Unit is named after the atmospheric ozone pioneer G.M.B. Dobson who carried out the
earliest studies on ozone in the atmosphere.

A Dobson Unit measures the total amount of ozone in an overhead column of the atmosphere.
Dobson Units are measured by how thick the layer of ozone would be if it were compressed into one layer at
0 degree Celsius and with a pressure of one atmosphere above it. Every 0.01 millimeter thickness of the layer
is equal to one Dobson Unit.

The average amount of ozone in the stratosphere across the globe is about 300 DU Highest levels of
ozone are usually found in the mid to high latitudes 360DU).
When stratospheric ozone falls below 200 DU this is considered low enough to represent the
beginnings of an ozone hole.
Formation of Ozone
The ozone is produced by the photolysis of oxygen molecules into oxygen atoms, followed by the
reaction of one oxygen atom with an oxygen molecule.
O2 + UV light → O + O
O + O2 + M →O3 + M
Where, M= Third body such as Nitrogen
2 O2 + UV light → O + O3
Ozone-depleting Substances
Ozone depleting substances (ODSs) are those substances which deplete the ozone layer and are
widely used in refrigerators, air conditioners, fire extinguishers, in dry cleaning as solvents for cleaning,
electronic equipment and as agricultural fumigants.
Ozone depleting substances include:
 Chlorofluorocarbons (CFCs) - refrigerants, propellants and cleaning solvents,
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 Carbon tetrachloride (CCl4) - dry-cleaning solvent, as a refrigerant, and as a component in fire

extinguishers.
 Bromofluorocarbons (BFCs) – Fire extinguishers
 Hydrochlorofluorocarbons (HCFCs) - CFC substitutes

Mechanism of Ozone layer

In the stratosphere, the Cl and Br atoms are liberated from the parent compounds by the action of
ultraviolet light, e.g.
CFCl3 + electromagnetic radiation → CFCl2 + Cl
The chlorine atom changes an ozone molecule to ordinary oxygen
Cl + O3 → ClO + O2
The ClO destroys a second ozone molecule and recreates the original chlorine atom, which can repeat
the first reaction and continue to destroy ozone.
ClO + O3 → Cl + 2 O2

Effects of Ozone layer depletion

The effects of depletion of the Ozone Layer are mentioned below.

i. UV radiation causes sun- eye- diseases (cataract), skin diseases, skin cancer and damage to immune
system in our body.
ii. It damages plants and causes reduction in crop productivity.
iii. Prolonged human exposure to UV rays may lead to slow blindness called actinic keratitis. Enhanced
level of UV ray could lead to more people suffering from cataracts.
iv. UV- radiations damage fabrics, pipes, paints, and other non-living materials on this earth.
v. It contributes in the Global Warming. If the ozone depletion continues, the temperature around the
world may rise even up to 5.5 Celsius degrees .
Control measures of Ozone layer depletion
1. Minimize high altitude aircraft flights (oxygen reduction and water vapor deposition)
2. Minimize rocket flights (water vapor deposition)
3. Encourage growth of plants that produce oxygen
4. Discourage deforestation
5. Decrease releases of high temperature moisture to the atmosphere
6. Eliminate production and release of known ozone depleting chemicals (such as CFCs and HCFCs)
7. Try to use products which are labeled "Ozone-Friendly"
8. Vehicle air conditioning units should regularly be checked for leaks.
9. Replace halon fire extinguishers with alternatives (e.g. carbon dioxide or foam).
10. Suggest school activities to increase awareness of the problem and to initiate local action.

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