class 11

1. ENVIRONMENTPOLLUTION
Air pollution
The major problem that the atmosphere is being subjected to is pollution. Polluted air is harmful
to man and the biosphere on the whole, as well. Air pollution can be defined as 'the change of
composition of air by the addition of harmful substances like the industrial and automobile gases
and particulate matter.'
Sources of Air Pollution
Most of the sources of air pollution are related to man's activities as a result of the modern
lifestyle. Added to this are also natural causes like the volcanoes, anaerobic decomposition of
organic matter, atmospheric reactions, etc.
Burning of Fossil Fuels
Fossil fuels include petroleum and coal. Burning of coal produces a lot of smoke and dust
whereas burning of petrol mainly produces sulphur dioxide. In addition to these, the pollutants
include carbon monoxide (CO), carbon dioxide (CO2), nitrogen oxides, hydrocarbons,etc.
Automobiles
Petrol on combustion produces carbon monoxide, hydrocarbons, nitrogen oxides, sulphur
compounds, organic acids and ammonia and carbon particles.
Industries
Fertiliser Plants
They produce oxides, sulphur, nitrogen, hydrocarbons, particulate matter and fluorine.
Thermal Plants
Since they are coal based the pollutants are fly ash, soot and sulphur dioxide.
Textile Industries
They produce cotton dust, nitrogen oxides, chlorine, smoke and sulphur dioxide.
Steel Plants
They produce carbon monoxide, carbon dioxide, sulphur dioxide, phenol, fluorine, cyanide,
particulate matter, etc.
Volcanic eruptions release oxides of nitrogen that pollute the atmosphere.
Major Pollutants
There are six main categories of air pollutants:
 oxides of carbon
 sulphur dioxide
 oxides of nitrogen
 hydrocarbon
 inorganic particulate matter and aerosols
 organic particulate matter
Harmful Effects of the Pollutants in Air
The various categories of air pollutants and their harmful effects are summarised in the given
table:

2. Pollutant Source/Cause Effect
Carbon monoxide
Automobile exhaust,
photochemical reactions in
the atmosphere, biological
oxidation by marine
organisms, etc.
Affects the respiratory activity as
haemoglobin has more affinity for Co
than for oxygen. Thus, CO combines
with HB and thus reduces the oxygen-
carrying capacity of blood. This
results in blurred vision, headache,
unconsciousness and death due to
asphyxiation (lack of oxygen).
Carbon dioxide
Carbon Burning of fossil
fuels,depletion of forests
(that remove excess carbon
dioxide and help in
maintaining the oxygen-
carbon dioxide ratio).
Global warming as it is one of the
greenhouse gases.
Sulphur dioxide
Industries, burning of fossil
fuels, forest fires, electric
generation plants, smelting
plants, industnal boilers,
petroleum refineries and
volcanic eruptions.
Respiratory problems, severe
headache,reduced productivity of
plants, yellowing and reduced storage
time for paper, yellowing and damage
to limestone and marble, damage to
leather, increased rate of corrosion of
iron, steel, zinc and aluminium.
Hydrocarbons Polynuclear
Aromatic
Compounds(PAC) and
Polynuclear Aromatic
Hydrocarbons(PAH)
Automobile exhaust and
industries,leaking fuel tanks,
leaching from toxic waste
dumping sites and coal tar
lining of some water supply
pipes.
Carcinogenic (may cause leukemia)
Chlorofluoro carbons
(CFCs)
Refngerators, air
conditioners, foam shaving
cream, spray cans and
cleaning solvents.
Destroy ozone layer which then
permits harmful UV rays to enter the
atmosphere.
Nitrogen Oxides
Automobile exhausts,
burning of fossil fuels, forest
fires,electric generation
plants, smelting plants,
industnal boilers, petroleum
refineries and volcanic
eruptions
Forms photochemical smog, at higher
concentrations causes leaf damage or
affects the photosynthetic activities of
plants and causes respiratory
problems in mammals.
PAN - peroxylacetyl -
nitrate
Photochemical reactions of
hydrocarbons and nitrogen
oxides.
Irritation of eye, throat and respiratory
tract, damage to clothes, paint and
rubber articles, damage to leaves and
stomatal tissue in plants.

3. Effects of Air Pollution
Global Warming
Most of the solar radiation entering the earth's atmosphere is reflected back into the space.
However some of the heat is absorbed by the gases like the carbon dioxide. This serves to keep
the earth warm much like the greenhouses. Greenhouses are glasshouses which maintain a
temperature higher than the surroundings for the plants to grow and yield better. The other gases
that contribute to this are water vapour, methane, chlorofluorocarbons (CFCs) and nitrous oxide.
These gases are called the greenhouse gases.
While greenhouse effect is a necessary and natural phenomenon. Every year the temperature are
going up due to pollution and the levels of these greenhouse gases is also going up. This is called
global warming. According to estimates, at the current rate of increase, the average global
temperature will go up by 3oC to 8oC in the next 100 years.
This will have the following effects:
 Climate of different regions
 Distribution of plants and animals
 Disturbance in agriculture and food production
 Melting of snow caps and resultant increase in sea levels. This will submerge parts of
coastal cities of New York, London and other major cities.
Formation of Photochemical Smog
When pollutants like hydrocarbons and nitrogen oxides combine in the presence of sunlight,
smog is formed. This is a mixture of gases and since it is formed by photochemical reactions, it
is called the photochemical smog. The word 'smog' is derived from the two words-smoke and
fog.
It forms a yellowish brown haze especially during winter and hampers visibility. It also causes
many respiratory disorders and allergies as it contains polluting gases.
Formation of Acid Rain
Sulphur dioxide and nitrogen oxides react with water in the atmosphere producing sulphuric acid
and nitric acid. These acids come down along with the rain. This phenomenon is called acid rain.
The pH of acid rain varies from 3-6. The composition of acid rain is sulphuric acid, nitric acid
and weak carbonic acid.
It has the following adverse affects on the environment:
 Causes respiratory and skin disorders.
Particulate matter Lead
halides (lead pollution)
Combustion of leaded
gasoline products
Toxic effect in man.
Asbestos particles Mining activities
Asbestosis - a cancerous disease of
the lungs
Silicon dioxide
Stone cutting, pottery, glass
manufacturing and cement
industries.
Silicosis, a cancerous disease.
Biological matter like the
pollen grains
Flowers Allergy
Fungal spores, bacteria,
virus, etc
Microbes Infectious deseases

4.  Affects productivity of plants by damaging the leaves.
 Enters the soil and affects the soil pH and other conditions.
 Enters the ground and river waters which causes harm to the aquatic life.
 Causes damage to marble and thus damages buildings and monuments like the Taj Mahal
Control of Air Pollution
Air pollution can be controlled by different methods depending on the source and the pollutant.
The different methods are:
One of the major causes of air pollution is the automobiles. The fuels being used should be lead-
free as this will reduce the level of lead in the atmosphere. The carburetor should be cleaned
regularly and good quality fuel should be used.
The industrial pollution is best controlled at source. The polluting gases should be passed
through filters so that the harmful matter is removed before the waste gases are released out. The
toxic gases should be detoxified.
The domestic and industrial smoke producing units should have long chimneys to take the
polluting gases far above and then disperse over a larger area.
The pollution by sulphur dioxide is mainly due to coal-based industries. Alternate non-sulphur
containing fuel must be used.
For effective control and prevention of air pollution it is important to educate people and
create public awareness about the ill-effects of air pollution.
Photochemical smog
Photochemical smog occurs due to the action of sunlight on air pollutants, generating
photochemical reactions. The principal constituents of the photochemical smog are gaseous
hydrocarbons (leading to ozone formation) and oxides of nitrogen (NOx) that are a part of
automobile exhaust.)
The reaction of sunlight with hydrocarbons and NO2 results in a variety of chemical products.
One of these is ozone, made up of 3 atoms of oxygen (O3), which is an irritating noxious gas.
This type of smog is oxidizing in character because of the presence of O3, NO2 and some
photochemical oxidants.
Photochemical smog causes eyes irritation and coughs due to the presence of ozone and can lead
to respiratory problems and reduced physical (athletic) ability.
Formation of photochemical smog
When pollutants like hydrocarbons and nitrogen oxides combine in the presence of sunlight,
smog is formed. This is a mixture of gases and since it is formed by photochemical reactions, it
is called the photochemical smog. The word 'smog' is derived from the two words - smoke and
fog.
It forms a yellowish brown haze especially during winter and hampers visibility. It also is a
cause of many respiratory disorders and allergies as it contains polluting gases.
Photochemical smog is mainly composed of ozone (O3), peroxyacetyl nitrate (PAN) and NOx. It
is also known as brown air where solar radiation is intense. In seasons of lesser solar radiation or
areas, smog formation is incomplete and the air is referred to as grey air.

5. Acid rain
The oxides of nitrogen and sulphur are corrosive and poisonous. When in excess in the
atmosphere, these gases react with water (e.g., rain water) to form acids, and thus result into acid
rain.
Acid rain has the following harmful effects:
 It damages the nutrition level of leaves of the plants.
 Acid rain promotes corrosion.
 It damages the structures made of marble, cement and / or lime viz., historical
monuments.
 Acid rain harms the aquatic life viz., it kills fish etc.
 Acid rain leads to the loss of soil fertility.
Chemistry of acid rain
Normally while rain travels through the air, it dissolves floating chemicals and washes down
particles that are suspended in air. At the start of its journey raindrops are neutral (pH = 7). In
clean air, rain picks up materials that occur naturally such as dust, pollen, some CO2 and other
chemicals produced by lightening or volcanic activities. These substances make rain slightly
acidic (pH = 6), which is not dangerous. However, when rain falls through polluted air, it comes
across chemicals such as gaseous oxides of sulphur (SOx), oxides of nitrogen (NOx), etc.
These substances dissolve in falling rain making it more acidic than normal with pH range
between 5.6 -3.5. In some case, it's pH gets lowered to the extent of 2. This leads to acid rain.
The formed sulphuric acid and nitric acid remain as vapour at high temperatures. These begin to
condense as the temperature falls and mix with rain or snow, on the way down to the Earth and
make rain sufficiently acidic.
Harmful effects of acid rain
SOx, NOx mixed with water as acid rain causes plant, animal and material damage. Some of the
significant ill effects of acid rain are:
Damage to animals
Acid rain chemically strips waterways of necessary nutrients and lowers the pH to levels where
plants and animals cannot live. Most of the aquatic animals cannot survive when the pH is less
than 4. Some species of fish, such as salmon, die even when the pH is less than 5.5. Certain
species of algae and zooplankton are eliminated at pH less than 6. A reduction in the
zooplankton and bottom fauna ultimately affects the food availability for the fish population.
Damage to plants
Acidic water is dangerous to plants. Sulphuric and nitric acid rain washes nutrients out of the
soil, damages the bark and leaves of trees and harms the fine root hairs of many plants which are

6. needed to absorb water. Leaf pigments are decolorized because acid affects green pigment
(chlorophyll) of plants. Agricultural productivity is also decreased. Several non-woody plants,
such as barley, cotton and fruit trees like apple, pear, etc., are severely affected by acid rain.
Material damage
Metallic surfaces exposed to acid rain are easily corroded. Textile fabrics, paper and leather
products lose their material strength or disintegrate by acid rain.
Building materials such as limestone, marble, etc are weakened on reaction with acid rains
because of the formation of soluble compounds.
Thus, acid rain is dangerous for historical monuments.
Water Pollution
Based on source of pollution, the following types of water pollution are recognised
 Water pollution due to city wastes
 Water pollution due to agriculture
 Industrial water pollution
 Water pollution due to natural reasons
Based on severity of pollution, the water pollution could be classified as
 Dangerous / serious water pollution
 Mild and rectifiable water pollution
 Negligible water pollution
Quite frequently, a water pollution could find a place in two or more groups. For e.g.an
agricultural water pollution may be serious and industrial water pollution may be mild or sea
water may be polluted by agricultural chemical and underground water may be polluted by city
wastes.
Although all the above groupings are meaningful, it is more convenient if the classification based
on utility and location of water is considered for detailed discussion. In this classification,
drinking water pollution can be caused by its source and during its path of movement. Thus, the
ground water pollution and river water pollution may ultimately lead to drinking water pollution
when ground water or river is polluted. River water and underground water can lead to many
other complications other than drinking water pollution alone. It is to be observed that sea water
is significantly polluted, although no pollutant is directly added to sea (except accidental ship
leakage or sinking of ship etc). This is because, all polluted rivers lead to pollutants to sea and
due to continuous accumulation, and the concentration of pollutants in sea water gets increased
as the time passes.
Important Features of Water Pollution
 Water pollution can be point source or non - point source. That is, it can be caused near
the source of pollution or where source of pollution is sometimes far away from source.
 Nature also contributes to water pollution besides human activities.
 The concentration of pollutants is generally on reducing trend, as the water moves to
longer distances / depths and as the time passes.
 Not all pollutants in water are dangerous. And not all dangerous pollutants are really
harmful. Few pollutants are not dangerous immediately. But they may cause ill effects after
long time.

7.  The sensitivity to pollutants in drinking water is more connected to physiology of human
/ animal body than concentration of pollutant within safe range.
Major Water Pollutants
Current water pollution issues can be divided into the following categories:
 Sewage and other oxygen-demanding wastes,
 Infectious or disease causing agents,
 Plant nutrients,
 Synthetic organic chemicals, Radioactive substances
Sewage and other oxygen-demanding waste
Oxygen-consuming wastes comprise of raw sewage from municipalities and other wastes from
paper mills, tanneries, food-processing plants and agriculture; these cause a proliferation of
aerobic decomposers who consume dissolved oxygen (DO) in water more rapidly than it can be
replaced by the atmosphere. Organic matter undergoes oxidation in rivers under the action of
micro-organisms.
Biochemical oxygen demand (BOD) is a measure of demand for oxygen utilized by micro-
organism, during oxidation of organic matter. It is defined as the amount of oxygen in milligram
per liter or in ppm used by micro-organisms to degrade the organic matter. A high BOD value
indicates more polluted water.
Infectious or disease causing agents
These are the various pathogenic micro-organisms which may enter the water along with sewage
or other wastes. These microbes, mainly bacteria and viruses, can cause various diseases such as
cholera, typhoid, dysentery, gastroenteritis, polio, hepatitis etc. in the water supply drawn from
these sources
Plant nutrients
The presence of plant nutrients in lakes and slow-moving waters supports high population of
aquatic plants that on decay deplete dissolved oxygen (DO) making the survival of aquatic life
problematic.
.Synthetic organic compounds
Pesticides, detergents, chemical dyes and other industrial chemicals and their waste constitute
synthetic organic compounds. When present in water, these chemicals can act as toxic poisons
for plants, animals and humans.
Green house effect
The Greenhouse Effect
The concept of green house effect simply codifies all the effects due to trapping of radiation
within the earth's surface layer of atmosphere. The world 'Green house' is commonly used
because such effect was found first time in a green house (Green house is a controlled
atmosphere farm house made out of glass all round the surface). When plants were made to grow
under confined atmosphere, it was observed that earth's radiation (short wave) was received
inside the glass green house but was not able to be reflected back to atmosphere outside
glasshouse. This trapping of radiation (short waves) is called green house effect. Green house
effect can happen even without any plants being grown in green house.
This phenomenon was extrapolated to earth's atmosphere. The radiation received by earth but not
able to be reflected can become 'Green house' effect.

8. Mechanism of green house effect
While radiation is received by earth from sun, rays are absorbed by carbon dioxide, carbon
monoxide in the air. On receiving these strong rays, the earth absorbs part of them and reflects
back major part of it depending on its own capacity. Major part of it may be trapped in the air, if
its CO2 concentration is high or obstruction in the form of dust, cloud is strong.
Reasons for green house effect
a) Out of total air pollutants to be 1 x 1012 tons, manmade pollutants are 5 x 108tons.
b) 25% of world's green house gases are released by USA which supports 4% of global
population.
c) Carbon monoxide accounts for 50% air pollution
d) Suspended particulate matter (dusts of various types) form 15% of total pollution.
e) Over 15 million tons of carbon monoxide is added to the atmosphere every year.
f) The level of emission is increasing at a very fast rate. As compared to 1987, CO emission
during 1997 was 132 times more.
g) CO2 concetrations in the air has increased by more than 15% in the last 100 years, mainly due
to deforestations, burning of fuels, industrialisation and urbanisation. From 275 ppm Co2 during
1890 AD, its level has touched 316 mm in 1980. But in 10 years after 1980, it has increased to
350 ppm. This means CO2concentration in air has increased from 0.0275% to 0.0350%.
Impacts of green house effect
Change in the composition of air due to several human activities has brought about green house
effect. Green house effect has brought about following phenomenal changes. The severity of
these changes will aggravate further in the next 10-20 years. By 2040, CO2 level in air is
expected to reach a level of 450 ppm (0.04%).
 Increase in mean air temperature during various parts of year is to the tune of 0.8oC to
1.02oC as compared to their normal temperature.
 Increase in sea level is observed in some parts of world due to excess heating of air -
which has caused large scale melting of ice covers.
 Change in the rainfall patterns due to variations in the convectional current (both in time
and direction) caused by difference in heating pattern of earth's air.
 Change/shifts in seasons and seasonal characters throughout the globe. These may even
include shifts in classification of earth into temperate, subtropical and tropical climates.
 Major changes in water resources of world due to disturbances in hydrological cycles.
Heavy rainfall tracts are gradually converted into low rainfall tracts, many humid areas being
transformed into arid areas, ground water depletion is high and recharging is very low etc.
 Shifts in disease/pest cycles of plants and animals. Many insignificant pests / diseases are
attaining major proportions because composition of microbial population is affected by shift
in temperature and hydrological cycles.
 Reduced agricultural productivity and food shortage.
 Increased water shortage throughout the globe.
Prepared by BharatPaudel
GandakiBoarding School