The envelope of air that completely
surrounds the earth is known as atmosphere.
The atmosphere extends to about 1000 km
from the surface of the earth. But 99% of the total mass of the atmosphere is
found within 32 km.
This is because the atmosphere is held by
the gravitational pull of the earth.
- Composition of the atmosphere.
Nitrogen – 78%
Oxygen – 21%
Argon – 0.93%
Carbon dioxide – 0.03%
Neon – 0.0018%
Helium – 0.00005%
Ozone – 0.0006%
Hydrogen – 0.00005%
Carbon dioxide: it is present in small quantity in the
atmosphere. It is an important constituent of air because it has the ability to
absorb heat and thus keep the atmosphere warm, thereby, balancing the heat of
the earth.
Water vapour: it is the most significant component of the
atmosphere as far as its effect on weather is concerned although its quantity
varies considerably from practically none (0) to upto about 4% by volume. Water
vapour is the source of all clouds and precipitation (rain, hail storm etc.).
water vapour , like carbon dioxide, has the ability to absorb heat energy. It
also regulates the hydrological cycle.
Dust : intercepts and reflect incoming insolation.
The polluted particles present in the air
not only absorb larger amount of insolation but also greatly absorb the
terrestrial radiation. Dust in the atmosphere contributes to the red and orange
color of sunrise and sunset.
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