The dynamic layer surrounding the earth above its surface containing various gases, moisture, aerosols etc. is called atmosphere.
1. Atmosphere can be defined as the gaseous envelope surrounding the earth.
2. Atmosphere can be defined as a grand body from the earth surface to the outer space and composed of number of gases.
The estimated mass of the atmosphere is 5.6 x 1014 metric tones. It extends over about 400 km height and meteorological events and effects occur in it. The thickness of gaseous envelope is equal to 1% of the earth’s mean radius.
Usefulness of the atmosphere:
1. It fulfils the biological oxygen demand (BOD) of the animal life.
2. It supplies the necessary precipitation or moisture.
3. It protects the biological life on the planet from harmful extraterrestrial radiations like UV, by absorbing it though ozone.
4. It maintains the warmth of the plannet through its green house effect, avoiding the temperature to fall to too extreme limits.(The earth’s temperature in the absence of atmosphere would have been +950C (day),and -1450C (Night)
5. It provides the necessary CO2 which is basic input required to run photosynthesis process in plants to build biomass.
6. It provides the necessary medium for the transport of pollens. Seeds spores and insets.
7. Many physical chemical and hydrological processes responsible for weather and climate occur in atmosphere only.
8. Atmosphere is a big reservoir of nitrogen. Some plants and microbes can fix this nitrogen for plant growth eg, Azolla pinara Azotobacter.
Composition of the atmosphere:
The various constituents of the atmosphere can be divided into following three categories.
Structure of Atmosphere,
|1||GASES||Moisture||Solid impurities or Aerosols|
|1.||Nitrogen(N2)||Water Vapour||1||Dust particles|
|3.||Argon (Ar)||3||Salt particles|
|4.||Carbon dioxide (CO2)||4||Water droplets and ice crystals.|
|6.||Sulphur dioxide (NO2)||6.||Pollen grains|
|7.||Nitrogen dioxide (NO2)|