Composition and Structure of Atmosphere

We eat food to three times a day and drink water more frequently but breathe every few seconds.
Air is essential to the survival of organisms.
Some organisms like humans may survive for some time without food and water but cannot survive even a few minutes without breathing air .
Atmosphere is a mixture of different gases and it envelops the earth all round.
It contain life giving gases like oxygen for humans and animals and carbon dioxide for plants.
The air is an integral part of the Earth's mass and 99% of the total mass of the atmosphere is confined to the height of 32 km from the Earth surface .
The air is colorless and odourless and can be felt only when it blows as wind.

Composition of the atmosphere

The atmosphere is composed of gases, water vapour and dust particles.
The portion of gas changes in the higher layer of the atmosphere in such a way that Oxygen will be almost in negligible quantity at the height of 120 km.
Carbon dioxide and water vapour are found only up to 90 km from the surface of the earth.

Carbon dioxide is Meteorological a very important gas as it is transparent to the incoming solar radiation but opaque to the outgoing Terrestrial radiation.
It absorbs a part of Terrestrial radiation and reflect back some part of it towards the Earth surface.
It is largely responsible for the greenhouse effect.
The volume of other gases is constant but the volume of carbon dioxide has been rising in the past few decades mainly because of the burning of fossil fuels .
Ozone is another important component of the atmosphere found between 10 and 50 km above the Earth's surface and act as a filter and absorb the ultraviolet rays radiating from the sun and prevents them from reaching the surface of Earth.

Water vapour is also a variable gas in the atmosphere, which decrease with altitude.
In the warm and wet tropics, it may account for 4% of the air by volume while in the dry and cold areas of desert and polar regions, it may be less than 1% of the air.
Water vapour also decrease from the equator toward the pole .
It also absorb part of the insolation from the sun and preserves the earth's radiated heat .
Water vapour also contributes to the stability and instability in the air .

Atmosphere has a sufficient capacity to keep small solid particles, which may originate from different sources and include sea salts, fine soil, smokes soot ash, pollen,dust and distantegrated particle of meteors.
The higher concentration of dust particle is found in subtropical and temperate region due to drive wind in comparison to equatorial and polar regions.

The atmosphere consists of different layers with varying density and temperature .
Density is highest near the surface of the earth and decrease with increasing altitude.
The column of atmosphere is divided into 5 different layer depending upon the temperature condition .
They are: troposphere , stratosphere, mesosphere, thermosphere and exosphere .

The troposphere is a lower most layer of atmosphere.
Its average height is 13 km and extends roughly to the height of 8 km near the poles and about 18 km at the equator .
Thickness of the troposphere is greatest at the equator because it is transported to the great heights by strong convectional currents .
This layer contained dust particle and water vapours.
All changes in climate and weather take place in this layer.
The temperature in this layer decrease at the rate of 1 Degree Celsius of every 165 M of height .
This is the most important layer for all biological activitiy.
The zone separating the troposphere from stratosphere is known as the tropopause .
The air temperature at the top of pores is about minus 80 degrees celsius over the equator and about minus 45 degree Celsius over the poles .
The temperature here is nearly constant and hence it is called the tropopause.

The stratosphere is found above that tropopause and extend up to the height of 50 km.
One important feature of the stratosphere is that it contain the Ozone Layer.
This layer absorbs ultraviolet radiation and shield life on the earth from instense, harmful form of energy .

The mesosphere lie above the stratosphere, which extends up to a height of 80 km.
In this layer, once again, temperature starts decreasing with the increase in altitude and reaches upto minus 100 degree Celsius at the height of 80 km.
The upper limit of measopause is known as the mesopause.

I ionosphere is located between 80km and 400 km above the mesopause.
It contains electrically charged particles known as the mesopause.
The ionosphere is located between 80km and 400 km above the mesopause.
It contain electrically charged particle known as iron and hence, it is known as ionosphere.
Radio wave transmitted from the earth and reflected back to the earth by this layer .
Temperature here starts increasing with height .
The uppermost layer of atmosphere above the thermosphere is known as exosphere.
This is the highest layer but very little is known about it .
These are extremely rarefied in this layer,and it gradualley marges with the outer surface .

The main elements of atmosphere which are subject to change and which influence human life on earth are temperatur, pressure ,wind, humidity cloud and precipitation.