Q: Can we use the kinetic theory of gases to calculate the temperature of the atmosphere ?
Sol: No , because the gas in the atmosphere is of very large extent and its weight is not negligible . The kinetic theory holds for a small body of a gas in thermal equilibrium . The pressure variation in the atmosphere is governed by gravity , that is , here the upward force on a thin layer due to the pressure difference is balanced by the weight of the air in the layer . In short we may say that the atmosphere is a system which is in mechanical equilibrium and not in thermal equilibrium .