Page 198 - Chemistry ICSE Class IX

186 ICSE Chemistry – 9
ƒ Thermosphere. Above mesosphere, the layer of thermosphere
begins. In thermosphere, temperature increases with altitude.
What is the average composition of the air

The average composition of the air near the earth’s surface is given below
in Table 8.1.

Table 8.1 Composition of the air near the surface of the earth
Proportion Proportion
Gas Gas
(% by volume) (% by volume)
Nitrogen (N ) 78.08 Krypton (Kr)
2
Oxygen (O ) 20.95 Hydrogen (H )
Major component of air: 2 2 Very small
EŝƚƌŽŐĞŶ͕ ŽdžLJŐĞŶ Argon (Ar) 0.93 Nitrous oxide (N O)
2
Minor components of air: Carbon dioxide (CO ) 0.03 Xenon (Xe)
2
ƌŐŽŶ͕ ĐĂƌďŽŶ ĚŝŽdžŝĚĞ͕ ǁĂƚĞƌ ǀĂƉŽƵƌ Neon (Ne) Water vapour (H O)
Trace components of air: 2 Variable (keep
,ĞůŝƵŵ͕ EĞŽŶ͕ <ƌLJƉƚŽŶ͕ yĞŶŽŶ͕ Helium (He) Very small Smoke Particles changing from
DĞƚŚĂŶĞ͕ ,LJĚƌŽŐĞŶ͕ KnjŽŶĞ͕ KdžŝĚĞƐ Methane (CH ) place to place
4
ŽĨ EŝƚƌŽŐĞŶ͕ ,LJĚƌŽŐĞŶ ƐƵůƉŚŝĚĞ and time to time)
Dust Particles
What is meant by the atmospheric pollution
Contamination of the atmospheric air with harmful toxic gases, smoke and
particulate matter, e.g., dust etc., is called atmospheric pollution.
Depending upon the region of the atmosphere which gets polluted,
the atmospheric pollution may be classi ed as follows:
ƒ Tropospheric pollution
ƒ Stratospheric pollution
Since we live in the tropospheric layer of the atmosphere, our
discussion of the atmospheric pollution is limited to the pollution of air in
the troposphere. Such pollution is therefore be called air pollution.
The air pollution may be de ned as follows:
Contamination of the air around us (in the troposphere) by harmful
toxic gases, smoke and particulate matter, beyond certain permissible
level is called air pollution.
The substances which cause air pollution are called air pollutants.
Air pollutants are of two types:
ƒ Gaseous pollutants, and
ƒ Particulate pollutants.
Gaseous Air Pollutants. The major gaseous air pollutants are:
ƒ Oxides of nitrogen, (NO ) – N O, NO and NO 2
2
x
ƒ Oxides of sulphur – SO and SO 3
2
ƒ Oxide of carbon – CO
ƒ Hydrogen sulphide – H S
2
ƒ Unburnt hydrocarbons (HC) – CH 4
Particulate Air Pollutants. The major particulate air pollutants are:
ƒ Aerosols
ƒ Dust, Cement dust, Asbestos dust
ƒ Fumes
ƒ Mist