NCERT Textbook - Pollution of Air and Water Class 8 Notes | EduRev

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Class 8 : NCERT Textbook - Pollution of Air and Water Class 8 Notes | EduRev

 Page 1


POLLUTION OF AIR AND WATER
POLLUTION OF AIR AND WATER
P
aheli and Boojho were very excited
to hear the news that Taj
Mahal in Agra is now one of the
seven wonders of the world. But they
were disappointed to hear that the
beauty of this monument in white
marble is being threatened by air
pollution in the area surrounding the
Taj. They were eager to know if
something can be done to fight the air
and water pollution.
We are all aware that our
environment is not what it used to be.
Our elders talk about the blue sky, clean
water and fresh air that was available
in their times. Now the media regularly
reports on the falling quality of the
environment. We ourselves feel the
impact of the falling quality of air and
water in our lives. The number of people
suffering from diseases of the respiratory
system, for example, is steadily rising.
We shudder to imagine a time when
clean air and water may no longer be
available! You have learnt about the
importance of air and water in your
previous classes. In this chapter, we will
study about the harmful changes taking
place in our surroundings and their
effects on our lives.
18.1 Air Pollution
W e can survive for some time without food,
but we cannot survive even for a few
minutes without air. This simple fact tells
us how important clean air is to us.
You already know that air consists
of a mixture of gases. By volume, about
78% of this mixture is nitrogen and
about 21% is oxygen. Carbon dioxide,
argon, methane, ozone and water
vapour are also present in very small
quantities.
Activity 18.1
You may have covered your nose
while passing a brick kiln emitting
smoke or started coughing while
walking on a busy road (Fig. 18.1).
On the basis of your experience,
compare the quality of air at the
places given below:
 A park and a busy road.
 A residential area and an
industrial area.
 A busy traffic  intersection at
different times of the day e.g.
early morning, afternoon and
evening.
 A village and a town.
Fig. 18.1 : A congested road in a city
Page 2


POLLUTION OF AIR AND WATER
POLLUTION OF AIR AND WATER
P
aheli and Boojho were very excited
to hear the news that Taj
Mahal in Agra is now one of the
seven wonders of the world. But they
were disappointed to hear that the
beauty of this monument in white
marble is being threatened by air
pollution in the area surrounding the
Taj. They were eager to know if
something can be done to fight the air
and water pollution.
We are all aware that our
environment is not what it used to be.
Our elders talk about the blue sky, clean
water and fresh air that was available
in their times. Now the media regularly
reports on the falling quality of the
environment. We ourselves feel the
impact of the falling quality of air and
water in our lives. The number of people
suffering from diseases of the respiratory
system, for example, is steadily rising.
We shudder to imagine a time when
clean air and water may no longer be
available! You have learnt about the
importance of air and water in your
previous classes. In this chapter, we will
study about the harmful changes taking
place in our surroundings and their
effects on our lives.
18.1 Air Pollution
W e can survive for some time without food,
but we cannot survive even for a few
minutes without air. This simple fact tells
us how important clean air is to us.
You already know that air consists
of a mixture of gases. By volume, about
78% of this mixture is nitrogen and
about 21% is oxygen. Carbon dioxide,
argon, methane, ozone and water
vapour are also present in very small
quantities.
Activity 18.1
You may have covered your nose
while passing a brick kiln emitting
smoke or started coughing while
walking on a busy road (Fig. 18.1).
On the basis of your experience,
compare the quality of air at the
places given below:
 A park and a busy road.
 A residential area and an
industrial area.
 A busy traffic  intersection at
different times of the day e.g.
early morning, afternoon and
evening.
 A village and a town.
Fig. 18.1 : A congested road in a city
SCIENCE 240
Fig. 18.3 : Air pollution due to automobiles
One of your observations in the
above activity could be the differences
in the amount of smoke in the
atmosphere. Do you know where the
smoke could have come from? Addition
of such substances to the atmosphere
modifies it. When air is contaminated
by  unwanted substances which have
a harmful effect on both the living and
the non-living, it is referred to as air
pollution.
18.2 How does Air Get Polluted?
The substances which contaminate the
air are called air pollutants. Sometimes,
such substances may come from natural
sources like smoke and dust arising from
forest fires or volcanic eruptions.
Pollutants are also added to the
atmosphere by certain human activities.
The sources of air pollutants are
factories (Fig. 18.2), power plants,
automobile exhausts and burning of
firewood and dung cakes.
Activity 18.2
You might have read in the
newspapers that respiratory
problems amongst children
are rising day by day. Conduct a
survey of households in your
neighbourhood and among friends
to find out how many children are
suffering from respiratory problems.
Many respiratory problems are
caused by air pollution. Let us now try
to find out the substances or pollutants
which are present in the polluted air.
Have you noticed how rapidly the
number of vehicles is increasing in our
cities?
Vehicles produce high levels of
pollutants like carbon monoxide, carbon
dioxide, nitrogen oxides and smoke (Fig.
18.3). Carbon monoxide is produced
from incomplete burning of fuels such
as petrol and diesel. It is a poisonous
gas. It reduces the oxygen-carrying
capacity of the blood.
Fig. 18.2 : Smoke from a factory
Do you know?
If the vehicles registered in Delhi are
lined up one after the other, the total
length would be nearly equal to the
combined lengths of the two longest
rivers in the world, Nile and Amazon!
Page 3


POLLUTION OF AIR AND WATER
POLLUTION OF AIR AND WATER
P
aheli and Boojho were very excited
to hear the news that Taj
Mahal in Agra is now one of the
seven wonders of the world. But they
were disappointed to hear that the
beauty of this monument in white
marble is being threatened by air
pollution in the area surrounding the
Taj. They were eager to know if
something can be done to fight the air
and water pollution.
We are all aware that our
environment is not what it used to be.
Our elders talk about the blue sky, clean
water and fresh air that was available
in their times. Now the media regularly
reports on the falling quality of the
environment. We ourselves feel the
impact of the falling quality of air and
water in our lives. The number of people
suffering from diseases of the respiratory
system, for example, is steadily rising.
We shudder to imagine a time when
clean air and water may no longer be
available! You have learnt about the
importance of air and water in your
previous classes. In this chapter, we will
study about the harmful changes taking
place in our surroundings and their
effects on our lives.
18.1 Air Pollution
W e can survive for some time without food,
but we cannot survive even for a few
minutes without air. This simple fact tells
us how important clean air is to us.
You already know that air consists
of a mixture of gases. By volume, about
78% of this mixture is nitrogen and
about 21% is oxygen. Carbon dioxide,
argon, methane, ozone and water
vapour are also present in very small
quantities.
Activity 18.1
You may have covered your nose
while passing a brick kiln emitting
smoke or started coughing while
walking on a busy road (Fig. 18.1).
On the basis of your experience,
compare the quality of air at the
places given below:
 A park and a busy road.
 A residential area and an
industrial area.
 A busy traffic  intersection at
different times of the day e.g.
early morning, afternoon and
evening.
 A village and a town.
Fig. 18.1 : A congested road in a city
SCIENCE 240
Fig. 18.3 : Air pollution due to automobiles
One of your observations in the
above activity could be the differences
in the amount of smoke in the
atmosphere. Do you know where the
smoke could have come from? Addition
of such substances to the atmosphere
modifies it. When air is contaminated
by  unwanted substances which have
a harmful effect on both the living and
the non-living, it is referred to as air
pollution.
18.2 How does Air Get Polluted?
The substances which contaminate the
air are called air pollutants. Sometimes,
such substances may come from natural
sources like smoke and dust arising from
forest fires or volcanic eruptions.
Pollutants are also added to the
atmosphere by certain human activities.
The sources of air pollutants are
factories (Fig. 18.2), power plants,
automobile exhausts and burning of
firewood and dung cakes.
Activity 18.2
You might have read in the
newspapers that respiratory
problems amongst children
are rising day by day. Conduct a
survey of households in your
neighbourhood and among friends
to find out how many children are
suffering from respiratory problems.
Many respiratory problems are
caused by air pollution. Let us now try
to find out the substances or pollutants
which are present in the polluted air.
Have you noticed how rapidly the
number of vehicles is increasing in our
cities?
Vehicles produce high levels of
pollutants like carbon monoxide, carbon
dioxide, nitrogen oxides and smoke (Fig.
18.3). Carbon monoxide is produced
from incomplete burning of fuels such
as petrol and diesel. It is a poisonous
gas. It reduces the oxygen-carrying
capacity of the blood.
Fig. 18.2 : Smoke from a factory
Do you know?
If the vehicles registered in Delhi are
lined up one after the other, the total
length would be nearly equal to the
combined lengths of the two longest
rivers in the world, Nile and Amazon!
POLLUTION OF AIR AND WATER 241
Boojho  remembers  seeing a thick
fog-like layer in the atmosphere,
especially during winters. This is smog
which is made up of smoke and fog.
Smoke may contain oxides of nitrogen
which combine with other air pollutants
and fog to form smog. The smog causes
breathing difficulties such as asthma,
cough and wheezing in children.
Many industries are also responsible
for causing air pollution. Petroleum
refineries are a major source of gaseous
pollutants like sulphur dioxide and
nitrogen dioxide. Sulphur dioxide is
produced by combustion of fuels like
coal in power plants. It can cause
respiratory problems, including
permanent lung damage.  You have
already studied about the burning of
fossil fuels in Chapter 5.
Other kinds of pollutants are
chlorofluorocarbons (CFCs) which are
used in refrigerators, air conditioners
and aerosol sprays. CFCs damage the
ozone layer of the atmosphere. Recall
that the ozone layer protects us from
harmful ultraviolet rays of the sun. Have
you heard of the ozone hole? Try to find
out about it. Thankfully, less harmful
chemicals are now being used in place
of CFCs.
In addition to the above mentioned
gases, automobiles which burn diesel
and petrol, also produce tiny particles
which remain suspended in air for long
periods (Fig. 18.3). They reduce
visibility. When inhaled, they cause
diseases. Such particles are also
produced during industrial processes
like steel making and mining. Power
plants give out tiny ash particles which
also pollute the atmosphere.
Activity 18.3
Prepare a table using the pollutants
mentioned above. You may even add
more data to the following Table.
Table 18.1
Air Pollutants Sources Effects
18.3 Case Study—
The Taj Mahal
Over the past 2 decades, Indiaís most
famous tourist attraction, Taj Mahal
located in Agra (Fig. 18.4), has become
a matter of concern. Experts have
warned that pollutants in air are
discolouring its white marble. So, it is
not only living organisms that get
affected by polluted air but non-living
things like buildings, monuments and
statues also get affected.
The industries located in and around
Agra like rubber processing, automobile,
chemicals and especially the Mathura oil
refinery, have been responsible for
producing pollutants like sulphur
dioxide and nitrogen dioxide. These
gases react with the water vapour present
in the atmosphere to form sulphuric acid
and nitric acid. The acids drop down with
rain, making the rain acidic. This is
called acid rain. Acid rain corrodes the
marble of the monument. The
phenomenon is also called ìMarble
cancerî. Suspended particulate matter,
such as the soot particles emitted by
Mathura oil refinery, has contributed
towards the yellowing of the marble.
The Supreme Court has taken
several steps to save the Taj. It has
Page 4


POLLUTION OF AIR AND WATER
POLLUTION OF AIR AND WATER
P
aheli and Boojho were very excited
to hear the news that Taj
Mahal in Agra is now one of the
seven wonders of the world. But they
were disappointed to hear that the
beauty of this monument in white
marble is being threatened by air
pollution in the area surrounding the
Taj. They were eager to know if
something can be done to fight the air
and water pollution.
We are all aware that our
environment is not what it used to be.
Our elders talk about the blue sky, clean
water and fresh air that was available
in their times. Now the media regularly
reports on the falling quality of the
environment. We ourselves feel the
impact of the falling quality of air and
water in our lives. The number of people
suffering from diseases of the respiratory
system, for example, is steadily rising.
We shudder to imagine a time when
clean air and water may no longer be
available! You have learnt about the
importance of air and water in your
previous classes. In this chapter, we will
study about the harmful changes taking
place in our surroundings and their
effects on our lives.
18.1 Air Pollution
W e can survive for some time without food,
but we cannot survive even for a few
minutes without air. This simple fact tells
us how important clean air is to us.
You already know that air consists
of a mixture of gases. By volume, about
78% of this mixture is nitrogen and
about 21% is oxygen. Carbon dioxide,
argon, methane, ozone and water
vapour are also present in very small
quantities.
Activity 18.1
You may have covered your nose
while passing a brick kiln emitting
smoke or started coughing while
walking on a busy road (Fig. 18.1).
On the basis of your experience,
compare the quality of air at the
places given below:
 A park and a busy road.
 A residential area and an
industrial area.
 A busy traffic  intersection at
different times of the day e.g.
early morning, afternoon and
evening.
 A village and a town.
Fig. 18.1 : A congested road in a city
SCIENCE 240
Fig. 18.3 : Air pollution due to automobiles
One of your observations in the
above activity could be the differences
in the amount of smoke in the
atmosphere. Do you know where the
smoke could have come from? Addition
of such substances to the atmosphere
modifies it. When air is contaminated
by  unwanted substances which have
a harmful effect on both the living and
the non-living, it is referred to as air
pollution.
18.2 How does Air Get Polluted?
The substances which contaminate the
air are called air pollutants. Sometimes,
such substances may come from natural
sources like smoke and dust arising from
forest fires or volcanic eruptions.
Pollutants are also added to the
atmosphere by certain human activities.
The sources of air pollutants are
factories (Fig. 18.2), power plants,
automobile exhausts and burning of
firewood and dung cakes.
Activity 18.2
You might have read in the
newspapers that respiratory
problems amongst children
are rising day by day. Conduct a
survey of households in your
neighbourhood and among friends
to find out how many children are
suffering from respiratory problems.
Many respiratory problems are
caused by air pollution. Let us now try
to find out the substances or pollutants
which are present in the polluted air.
Have you noticed how rapidly the
number of vehicles is increasing in our
cities?
Vehicles produce high levels of
pollutants like carbon monoxide, carbon
dioxide, nitrogen oxides and smoke (Fig.
18.3). Carbon monoxide is produced
from incomplete burning of fuels such
as petrol and diesel. It is a poisonous
gas. It reduces the oxygen-carrying
capacity of the blood.
Fig. 18.2 : Smoke from a factory
Do you know?
If the vehicles registered in Delhi are
lined up one after the other, the total
length would be nearly equal to the
combined lengths of the two longest
rivers in the world, Nile and Amazon!
POLLUTION OF AIR AND WATER 241
Boojho  remembers  seeing a thick
fog-like layer in the atmosphere,
especially during winters. This is smog
which is made up of smoke and fog.
Smoke may contain oxides of nitrogen
which combine with other air pollutants
and fog to form smog. The smog causes
breathing difficulties such as asthma,
cough and wheezing in children.
Many industries are also responsible
for causing air pollution. Petroleum
refineries are a major source of gaseous
pollutants like sulphur dioxide and
nitrogen dioxide. Sulphur dioxide is
produced by combustion of fuels like
coal in power plants. It can cause
respiratory problems, including
permanent lung damage.  You have
already studied about the burning of
fossil fuels in Chapter 5.
Other kinds of pollutants are
chlorofluorocarbons (CFCs) which are
used in refrigerators, air conditioners
and aerosol sprays. CFCs damage the
ozone layer of the atmosphere. Recall
that the ozone layer protects us from
harmful ultraviolet rays of the sun. Have
you heard of the ozone hole? Try to find
out about it. Thankfully, less harmful
chemicals are now being used in place
of CFCs.
In addition to the above mentioned
gases, automobiles which burn diesel
and petrol, also produce tiny particles
which remain suspended in air for long
periods (Fig. 18.3). They reduce
visibility. When inhaled, they cause
diseases. Such particles are also
produced during industrial processes
like steel making and mining. Power
plants give out tiny ash particles which
also pollute the atmosphere.
Activity 18.3
Prepare a table using the pollutants
mentioned above. You may even add
more data to the following Table.
Table 18.1
Air Pollutants Sources Effects
18.3 Case Study—
The Taj Mahal
Over the past 2 decades, Indiaís most
famous tourist attraction, Taj Mahal
located in Agra (Fig. 18.4), has become
a matter of concern. Experts have
warned that pollutants in air are
discolouring its white marble. So, it is
not only living organisms that get
affected by polluted air but non-living
things like buildings, monuments and
statues also get affected.
The industries located in and around
Agra like rubber processing, automobile,
chemicals and especially the Mathura oil
refinery, have been responsible for
producing pollutants like sulphur
dioxide and nitrogen dioxide. These
gases react with the water vapour present
in the atmosphere to form sulphuric acid
and nitric acid. The acids drop down with
rain, making the rain acidic. This is
called acid rain. Acid rain corrodes the
marble of the monument. The
phenomenon is also called ìMarble
cancerî. Suspended particulate matter,
such as the soot particles emitted by
Mathura oil refinery, has contributed
towards the yellowing of the marble.
The Supreme Court has taken
several steps to save the Taj. It has
SCIENCE 242
and a part is reflected back into space.
A part of the reflected radiation is
trapped by the atmosphere. The trapped
radiations further warm the earth. If you
have seen a greenhouse in a nursery or
elsewhere, recall that the sunís heat is
allowed to get in but is not allowed to
go out. The trapped heat warms the
green house. The trapping of radiations
by the earthís atmosphere is similar.
That is why it is called the greenhouse
effect. Without this process, life would
not have been possible on the earth. But
now it threatens life. CO
2
 
is one of the
gases responsible for this effect.
You know that CO
2
 is one of the
components of air. You have also studied
I am reminded of the
chapter on crops. I
wonder whether acid rain
affects the soil and
plants also.
But how does CO
2
 content
rise in the atmosphere and
become excessive?
ordered industries to switch to cleaner
fuels like CNG (Compressed Natural Gas)
and LPG (Liquefied Petroleum Gas).
Moreover, the automobiles should
switch over to unleaded petrol in the Taj
zone.
Discuss with your elders and see
what they have to say about the
condition of the Taj, 20 or 30 years ago!
Try to procure a picture of the Taj Mahal
for your scrap book.
18.4 Greenhouse Effect
You know that the sunís rays warm the
earthís surface. A part of the radiation
that falls on the earth is absorbed by it
Fig. 18.4 : Taj Mahal
Page 5


POLLUTION OF AIR AND WATER
POLLUTION OF AIR AND WATER
P
aheli and Boojho were very excited
to hear the news that Taj
Mahal in Agra is now one of the
seven wonders of the world. But they
were disappointed to hear that the
beauty of this monument in white
marble is being threatened by air
pollution in the area surrounding the
Taj. They were eager to know if
something can be done to fight the air
and water pollution.
We are all aware that our
environment is not what it used to be.
Our elders talk about the blue sky, clean
water and fresh air that was available
in their times. Now the media regularly
reports on the falling quality of the
environment. We ourselves feel the
impact of the falling quality of air and
water in our lives. The number of people
suffering from diseases of the respiratory
system, for example, is steadily rising.
We shudder to imagine a time when
clean air and water may no longer be
available! You have learnt about the
importance of air and water in your
previous classes. In this chapter, we will
study about the harmful changes taking
place in our surroundings and their
effects on our lives.
18.1 Air Pollution
W e can survive for some time without food,
but we cannot survive even for a few
minutes without air. This simple fact tells
us how important clean air is to us.
You already know that air consists
of a mixture of gases. By volume, about
78% of this mixture is nitrogen and
about 21% is oxygen. Carbon dioxide,
argon, methane, ozone and water
vapour are also present in very small
quantities.
Activity 18.1
You may have covered your nose
while passing a brick kiln emitting
smoke or started coughing while
walking on a busy road (Fig. 18.1).
On the basis of your experience,
compare the quality of air at the
places given below:
 A park and a busy road.
 A residential area and an
industrial area.
 A busy traffic  intersection at
different times of the day e.g.
early morning, afternoon and
evening.
 A village and a town.
Fig. 18.1 : A congested road in a city
SCIENCE 240
Fig. 18.3 : Air pollution due to automobiles
One of your observations in the
above activity could be the differences
in the amount of smoke in the
atmosphere. Do you know where the
smoke could have come from? Addition
of such substances to the atmosphere
modifies it. When air is contaminated
by  unwanted substances which have
a harmful effect on both the living and
the non-living, it is referred to as air
pollution.
18.2 How does Air Get Polluted?
The substances which contaminate the
air are called air pollutants. Sometimes,
such substances may come from natural
sources like smoke and dust arising from
forest fires or volcanic eruptions.
Pollutants are also added to the
atmosphere by certain human activities.
The sources of air pollutants are
factories (Fig. 18.2), power plants,
automobile exhausts and burning of
firewood and dung cakes.
Activity 18.2
You might have read in the
newspapers that respiratory
problems amongst children
are rising day by day. Conduct a
survey of households in your
neighbourhood and among friends
to find out how many children are
suffering from respiratory problems.
Many respiratory problems are
caused by air pollution. Let us now try
to find out the substances or pollutants
which are present in the polluted air.
Have you noticed how rapidly the
number of vehicles is increasing in our
cities?
Vehicles produce high levels of
pollutants like carbon monoxide, carbon
dioxide, nitrogen oxides and smoke (Fig.
18.3). Carbon monoxide is produced
from incomplete burning of fuels such
as petrol and diesel. It is a poisonous
gas. It reduces the oxygen-carrying
capacity of the blood.
Fig. 18.2 : Smoke from a factory
Do you know?
If the vehicles registered in Delhi are
lined up one after the other, the total
length would be nearly equal to the
combined lengths of the two longest
rivers in the world, Nile and Amazon!
POLLUTION OF AIR AND WATER 241
Boojho  remembers  seeing a thick
fog-like layer in the atmosphere,
especially during winters. This is smog
which is made up of smoke and fog.
Smoke may contain oxides of nitrogen
which combine with other air pollutants
and fog to form smog. The smog causes
breathing difficulties such as asthma,
cough and wheezing in children.
Many industries are also responsible
for causing air pollution. Petroleum
refineries are a major source of gaseous
pollutants like sulphur dioxide and
nitrogen dioxide. Sulphur dioxide is
produced by combustion of fuels like
coal in power plants. It can cause
respiratory problems, including
permanent lung damage.  You have
already studied about the burning of
fossil fuels in Chapter 5.
Other kinds of pollutants are
chlorofluorocarbons (CFCs) which are
used in refrigerators, air conditioners
and aerosol sprays. CFCs damage the
ozone layer of the atmosphere. Recall
that the ozone layer protects us from
harmful ultraviolet rays of the sun. Have
you heard of the ozone hole? Try to find
out about it. Thankfully, less harmful
chemicals are now being used in place
of CFCs.
In addition to the above mentioned
gases, automobiles which burn diesel
and petrol, also produce tiny particles
which remain suspended in air for long
periods (Fig. 18.3). They reduce
visibility. When inhaled, they cause
diseases. Such particles are also
produced during industrial processes
like steel making and mining. Power
plants give out tiny ash particles which
also pollute the atmosphere.
Activity 18.3
Prepare a table using the pollutants
mentioned above. You may even add
more data to the following Table.
Table 18.1
Air Pollutants Sources Effects
18.3 Case Study—
The Taj Mahal
Over the past 2 decades, Indiaís most
famous tourist attraction, Taj Mahal
located in Agra (Fig. 18.4), has become
a matter of concern. Experts have
warned that pollutants in air are
discolouring its white marble. So, it is
not only living organisms that get
affected by polluted air but non-living
things like buildings, monuments and
statues also get affected.
The industries located in and around
Agra like rubber processing, automobile,
chemicals and especially the Mathura oil
refinery, have been responsible for
producing pollutants like sulphur
dioxide and nitrogen dioxide. These
gases react with the water vapour present
in the atmosphere to form sulphuric acid
and nitric acid. The acids drop down with
rain, making the rain acidic. This is
called acid rain. Acid rain corrodes the
marble of the monument. The
phenomenon is also called ìMarble
cancerî. Suspended particulate matter,
such as the soot particles emitted by
Mathura oil refinery, has contributed
towards the yellowing of the marble.
The Supreme Court has taken
several steps to save the Taj. It has
SCIENCE 242
and a part is reflected back into space.
A part of the reflected radiation is
trapped by the atmosphere. The trapped
radiations further warm the earth. If you
have seen a greenhouse in a nursery or
elsewhere, recall that the sunís heat is
allowed to get in but is not allowed to
go out. The trapped heat warms the
green house. The trapping of radiations
by the earthís atmosphere is similar.
That is why it is called the greenhouse
effect. Without this process, life would
not have been possible on the earth. But
now it threatens life. CO
2
 
is one of the
gases responsible for this effect.
You know that CO
2
 is one of the
components of air. You have also studied
I am reminded of the
chapter on crops. I
wonder whether acid rain
affects the soil and
plants also.
But how does CO
2
 content
rise in the atmosphere and
become excessive?
ordered industries to switch to cleaner
fuels like CNG (Compressed Natural Gas)
and LPG (Liquefied Petroleum Gas).
Moreover, the automobiles should
switch over to unleaded petrol in the Taj
zone.
Discuss with your elders and see
what they have to say about the
condition of the Taj, 20 or 30 years ago!
Try to procure a picture of the Taj Mahal
for your scrap book.
18.4 Greenhouse Effect
You know that the sunís rays warm the
earthís surface. A part of the radiation
that falls on the earth is absorbed by it
Fig. 18.4 : Taj Mahal
POLLUTION OF AIR AND WATER 243
the role of carbon dioxide in plants. But
if there is excess of CO
2
 in the air, it
acts as a pollutant.
Can you help Paheli find out  the
answer to her question?
On the one hand, CO
2
 is continuously
being released because of human
activities. On the other hand, area under
forests is decreasing. Plants utilise CO
2
from the atmosphere for photosynthesis,
thereby decreasing the amount of CO
2
in the air. Deforestation leads to an
increase in the amount of CO
2
 in the air
because the number of trees which
consume CO
2
 is reduced. Human
activities, thus, contribute to the
accumulation of CO
2
 in the  atmosphere.
CO
2
 traps heat and does not allow it to
escape into space. As a result, the average
temperature of the earthís atmosphere
is gradually increasing. This is called
global warming.
Other gases like methane, nitrous
oxide and water vapour also contribute
Global Warming
A Serious Threat!
Global warming can cause sea levels
to rise dramatically. In many places,
coastal areas have already been
flooded. Global warming could result
in wide ranging effects on rainfall
patterns, agriculture, forests, plants
and animals. Majority of people living
in regions which are threatened by
global warming are in Asia. A recent
climate change report gives us only
a limited time to keep  the greenhouse
gases at the present level. Otherwise,
the temperature may rise by more
than 2 degrees Celsius by the end of
the century, a level considered
dangerous.
towards this effect. Like CO
2
, they are
also called greenhouse gases.
Global warming has become a major
concern for governments worldwide.
Many countries have reached an
agreement to reduce the emission of
greenhouse gases. The Kyoto Protocol
is one such agreement.
Boojho is surprised to hear that an
increase in the earthís temperature by
even as little as 0.5 ?C can have such a
serious effect!  Paheli tells him that she
had read in the newspapers recently that
the Gangotri glacier in the Himalayas
has started melting because of global
warming.
18.5 What can be Done?
What can we do to reduce air
pollution?
There are many success stories in our
fight against air pollution. For example,
a few years ago, Delhi was one of the
most polluted cities in the world. It was
being choked by fumes released from
automobiles running on diesel and
petrol. A decision was taken to switch
to fuels like CNG (Fig. 18.5) and
Fig. 18.5 : A  public transport bus powered by CNG
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