Question

why air temperature decrease with altitudes

Answer 1

Heya,

Answer to you question is:-

The farther away you get from the earth, the thinner the atmosphere gets. The total heat content of a system is directly related to the amount of matter present, so it is cooler at higher elevations.

HOPE THIS HELPS YOU:-))
@ashu

Answer 2

In the earths atmosphere, pressure, which is related to the number of molecules per unit volume, decreases exponentially with altitude. Thus, if a parcel of air from the surface rises (because of wind flowing up the side of a mountain, for example), it undergoes an expansion, from higher to lower pressure.