Composition of the Atmosphere

In this lesson we shall understand about earth’s atmosphere. Our atmosphere is a gaseous envelope extending up to 800 kilometres over the surface of earth. 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 is 3:1 by weight. It is common knowledge that the amount of oxygen present in the atmosphere reduces with increase in height. Therefore, supplementary oxygen is required about 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.

The distribution of air mass in our atmosphere is something like this. 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.