Atmosphere : Composition & Structure

Atmosphere

An atmosphere is a layer of gases surrounding a planet or other material body of sufficient mass that is held in place by the gravity of the body. An atmosphere is more likely to be retained if the gravity is high and the atmosphere's temperature is low.

Here we will study the composition & structure of our Planet Earth.

Composition of Atmosphere

Gases water vapors and particulates jointly composed the atmosphere. Water vapor, dust particulates and ozone are very important for the climatic conditions of the world. Up to 50km the atmosphere is composed of –

• Nitrogen - 78%
• Argon - 0.93%
• Oxygen - 21%
• Carbon Dioxide - 0.03%

Others are Neon, Helium, Ozone, Hydrogen, etc.

Oxygen (21%)

• This is the life giving gas.
• Green plants produce it during the process of photosynthesis.
•  Nothing is burned without oxygen so it is the source of energy.

Carbon Dioxide (.03%)

• It is a heavy gas so it is situated in the lowest portion of Atmosphere.
• It is permeable for the incoming solar radiations but opaque for the outgoing terrestrial radiations.
• In this way, by trapping the heat, it works as a green house gas.

Ozone

• It acts as a filter and absorbs the harmful ultraviolet rays.
• Nitrogen oxide released by the jet planes and Chlorofluorocarbons (CFC), Hydro fluorocarbons (HFC) used and released by the air conditioners, refrigerators etc. are very harmful gases for ozone layer. They are resulting in depletion of this layer.

Structure of Atmosphere

It is composed of five layers above the earth’s surface.

Troposphere

• It is the lower most and the most important layer of the atmosphere, as almost all the weather phenomena occur in this layer.
• The average height of the troposphere is about 16-18km over the equator and 6-8km over the poles.
• Temperature decreases with increasing height at a rate of 1˚ /165m or 6.5˚ /1000m in this layer.

Stratosphere

• Temperature remains stable at the beginning of this layer but suddenly it starts changing after the height of 20km.
• This sudden change in temperature is due to the presence of ozone layer, which absorbs the ultraviolet rays from the weather.
• This layer is free from almost all weather disturbances, hence is preferred by the pilots to fly their airplanes.
• This layer extends between 18km to 32km.

Mesosphere

• This layer extends between 32km-80km.
• Temperature again decreases with increasing height and reaches up to -100°ᶜ, which is the minimum temperature of the atmosphere.

Ionosphere

• It extends from 80 to 640km.
• Electrically charged or ionized particles are abundantly found in this layer and temperature increases with increasing height.
• This layer reflects back the radio waves.

Exosphere

• It represents the upper most layer of the atmosphere.
• It extends beyond 640km of height from the sea level.
• Electrically charged particles are also found abundantly in this layer and there are separate layers of N2, O2, He, and H2.