Question

Describe the composition of the Earth’s atmosphere, including the variation with altitude of the temperature, pressure and density.

Answer 1

Composition of earth's atmosphere - 78.084% Nitrogen, 20.946% Oxygen, 0.934% Argon, 0.04% Carbon Dioxide, 0-5% Water Vapour, Rest Neon, Helium Methane etc.

Variation of pressure.

The pressure is about 1 atm or 1.01 *10^5 Pa at sea level and decreases exponentially. It almost reaches 0 at around 30 km altitude and keeps on tending to zero.

Variation of temperature:

At troposphere 0-12 km heat from the earth warms the atmosphere and as the air is thnner at high altitudes the temperature decreases with altitude going from about 20^oC (Earth average) to - 60^oC. After that comes the stratosphere which lies till about 47-48 km and here the temperature increases with altitute as it is the ozone layer which traps UV rays After this in the mesosphere (till about 80 km) again the temperature decreases due to thinning of air and finally in the thermosphere it again increases as this layer contains Nitrogen and oxygen molecules that trap solar X-Rays.

Variation of density

Density of air, like air pressure, decreases as altitude increases. It also changes with variation in atmospheric pressure, temperature and humidity. It increases exponentially and at the suraface at 1 atm pressure and 15 ^oC the air pressure is 1.225 kg/m³.