Composition of the Atmosphere

Our atmosphere is a gaseous envelope extending up to 800 kilometres over the surface of earth. In this lesson we shall understand about earth’s atmosphere and its impact on Meteorology. In our earlier post, we had learnt about the scope of Aviation Meteorology for Pilot Licence Examinations.


The atmosphere is attached to the earth by the gravitational pull of the earth. Therefore, it moves at the same speed as that of earth. Atmosphere is made-up of many gases. The main constituents of the atmosphere are Nitrogen which constitutes 78%, Oxygen constituting 21% and other Trace gasses constituting the remaining 1%.

The ratio of nitrogen to oxygen by volume is 4:1 and by weight it is 3:1. It is common knowledge that the amount of oxygen present in the atmosphere reduces with increase in height. Due to the lack of oxygen, supplementary oxygen is required in flights above 10,000 feet.


Up to 80 kilometres from the surface of earth, the constituents of the earth are constant. This part of the atmosphere is called as the Homosphere. On the other hand above 80 kilometres the constituents are not constant. Therefore, atmosphere above 80 KM is called as Heterosphere.


Density of any fluid is defined as the mass per unit volume. Air density is maximum at the surface of earth and reduces with increase in height. Approximately 50% of the atmosphere is present between the surface of the earth and 6 kilometres from the earth’s surface. Around 75% off the air mass would be present within 10 kilometres from the surface. Finally 99% of the air mass would be present within 35 kilometres from the surface.

In this lesson we have understood about the constituents of the atmosphere. In our next post, we shall proceed to learn about the Trace Gasses in the Atmosphere.