Atmosphere

Atmosphere

Composition of Atmosphere

For our clear understanding and proper studies the components of the atmosphere can be broadly be divided into three categories on the basis of the volume content as: Major, Minor and Trace.

Category	Gas Name	Chemical Formula	Percent Volume
Major	Nitrogen	N₂	78.08%
	Oxygen	O₂	20.95%
	* Water vapour	H₂O	0-4%
Minor	Argon	Ar	0.93%
	*Carbon dioxide	CO₂	0.036%
Trace	Neon	Ne	0.0018%
	Helium	He	0.0005%
	*Methane	CH₄	0.00017%
	Krypton	Kr	0.000114%
	*Nitrous oxide	N₂O	0.00003%
	Hydrogen	H₂	0.00005%
	Xenon	Xe	0.00009%
	Sulphur Dioxide	S₂O	*0.000000
	Ozone	O₃	0.000004%
	Ammonia	NH₃	*0.000000

From the above data we come to know that two major gases of the atmosphere Nitrogen and Oxygen only constitute to about more than 99% of the total gases in the atmosphere. Remaining other minor and the trace amount of gases constitute to about 1%of total gsases. The other gases like water vapour, carbondioxide,etc are at the state of its changing volume on the atmosphere. And the ramaining other gases except Argon are only at the trace amount in the atmosphere.

Layer of Atmosphere	Altitude range (in Km.)	Temperature range(in °C)	Important chemicals In symbols
Troposphere	0-11	15-56	N₂,O₂,CO₂,H₂O
Stratosphere	11-50	-56to -2	O₃
Mesosphere	50-85	-2 to-92	O₂⁺,No⁺
Thermosphere	85-500	-92 to 1200	O₂⁺,O⁺,No⁺

Troposphere: It contains 70% of the total mass of the atmosphere. The upper limit of the Troposphere may vary by a km or more depending upon the factors such as Temperature and nature of the terresterial surfaces. Density decreases exponentially with increasing in altitude. It is particularly due to general circulation of the Earth. In Troposphere temperature decreases with increasing altitude. The layer that differentiate the Troposphere and Stratosphere is known as Tropopause which has -56°C of temperature in average.

Stratosphere: In the Stratosphere temperature increases with increases in the altitude with a maximum of -2°C at the upper limit of the atmosphere. Ozone in this region absorb ultraviolet rays and raises the temperature causing the positive lapse rate. It plays an important role in the Stratosphere in blocking the ultraviolet rays to come down to the Earth surface so, it acts as a protective shield for the life on Earth from the injurious effect of the suns ultraviolet rays. And at the same time it supplies heat source for partitioning the atmosphere into quiescent stratosphere and turbulent strarosphere.

In Stratosphere, there is cycle of formation of Ozone & destruction of ozone simultaneously in natural condition but after releasing ozone destructing pollutants from the atmosphere by anthropogenic activities the natural cycle can be disturbed. So, the amount of formation of ozone is lessler than destruction of Ozone.

Mesosphere: In mesosphere, temperature falls alternatively. It is due to low level of ultraviolet rays absorbing chemical species. The temperature may vary from -2°C to -92°C.

Thermosphere: The temperature raise once again and reaches upto 1200°C. Atmospheric gases particularly oxygen and nitric oxide split into atoms and also undergo ionization after absorption of the solar radiation.