Page 207 - Science Class 08

v Promo ng unleaded petrol and diesel. the influence of different forces. It can be done
v Correc ng the engine design to improve
combus on so to minimise the exhaust of
smoke and harmful gases.
v Using Compressed Natural Gas (CNG).
v Filters should be used in vehicles to
capture and recycle, the escaped gases
(hydrogen) from the engine.
Nowadays, cars are fi ed with a special system
called cataly c converter which convert
harmful gases like CO and NO into harmless
2
2
carbon dioxide, nitrogen and water. This system
should be promoted sincerely.
Removal of Par culate Ma er : This method
involves collec on of par culate ma er under
1. What is pollu on?
2. What are the natural causes responsible for air pollu on?
3. What do you mean by SPM?
4. Name any three harmful gases that make the air polluted.
5. What does cause the deple on of ozone layer?
6. What is the func on of electrosta c precipitator?
WATER POLLUTION
Water is essen al for all living beings. Without
pure water, we cannot live. You should
remember that only 1 percent of the total
available water on the earth is potable which
we can obtain from rivers, lakes, ponds and
from the beneath the earth’s surface in the
form of groundwater. The largest amount of
water is present in the seas and oceans. We
cannot use the water of seas or ocean because
it is salty.
The surface of groundwater supply is called the
water table. Due to over exploita on of the
groundwater, it is deple ng rapidly. Ground-
Science-8
in the following ways.
Fabric Filters : In this system, polluted air
containing par culate ma er is passed through
fabric filters. The fabric filters absorb the SPM
and make air clean.
Wet Scrubbers : These are special tanks in
which air pollutants are sprayed by jets of
water before they reach the chimney. In this
way, water washes away the par culate ma er.
Electrosta c Precipitator : To remove SPM
from gas steam, the electrical forces are
applied within the chamber in the
precipita on. The charged and ionised par cles
are a racted to charged electrodes and
removed. This process can remove 99% of the
par culate ma er from the chimney exhaust.
water is being used up faster than it is being
replenished. Besides, we have cut down trees
which help in recharging the ground water.
Now, you can imagine how much water is le
for us. What will happen if we pollute the
remaining sources of potable water?
Water is a great solvent, which makes it
polluted very easily. The water is polluted, in
every use to which it is put — washing, irrig-
a on, flushing away wastes, cooling, making
paper, etc. adds something to water.
The term water pollu on is referred to as any
type of water contamina on, so that its use by
living beings become hazardous to health.
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