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SAI International School
Subject - Chemistry
Class - VIII
Topic –Pollution of air and water
Sub Topic-Introduction, Air pollution, Causes of air pollution

LESSON NOTES

Introduction

Air is a mixture of gases. The two main gases present in the air are nitrogen and oxygen.
The various components of air are, Nitrogen (78%), Oxygen (21%), and the remaining 1 %
includes gases like Carbon dioxide, Argon, Water vapour, etc. This is the normal
composition of air and is good for us.

The presence of unusually high concentrations of harmful or poisonous substances in the
environment (air, water, etc.) is called pollution.

Pollution contaminates the environment and makes them impure to such an extent that they
become harmful to the flora and fauna, as well as to the non-living things.
An unwanted and harmful substance that contaminates the environment is called a
pollutant. In other words, a substance that causes pollution is called a pollutant.

In addition to the normal constituents of air, the polluted air may also contain harmful
substances such as carbon monoxide, sulphur dioxide, nitrogen oxides, smoke, dust, etc.

Air Pollution
The contamination of air with harmful gases like sulphur dioxide, nitrogen oxides, etc., is
called air pollution. The substance whose presence in the air makes it impure or
contaminated is called an air pollutant. A substance becomes an air pollutant when it is
present in the air in such concentration which is high enough to harm the living or non-living
things.

The major pollutants which cause air pollution are: Sulphur dioxide, Nitrogen oxides,
Carbon monoxide, excess of Carbon dioxide, Chlorofluorocarbons, and suspended
particulate matter (such as Dust, Smoke and Fly ash).

Sources of Air Pollution

Most of the air pollution is caused by the burning of fuels such as wood, cow-dung cakes,
coal, kerosene, petrol and diesel in homes, motor vehicles, factories and thermal power
plants, etc. the various sources of air pollution are given below:

a. Smoke emitted from homes by the burning of fuels like wood, cow-dung cakes,
kerosene and coal causes air pollution.
b. Exhaust gases emitted by motor vehicles due to the burning of petrol and diesel
cause air pollution. Motor vehicles are the major cause of air pollution in big cities.
c. Smoke emitted by factories and thermal power plants due to burning of coal causes
air pollution.
d. Oil refineries and industries engaged in the production of metals and manufacture of
chemicals cause air pollution.

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