<P> The word troposphere is derived from the Greek tropos (meaning "turn, turn toward, change") and sphere (as in the Earth), reflecting the fact that rotational turbulent mixing plays an important role in the troposphere's structure and behaviour . Most of the phenomena associated with day - to - day weather occur in the troposphere . </P> <P> By volume, dry air contains 78.08% nitrogen, 20.95% oxygen, 0.93% argon, 0.04% carbon dioxide, and small amounts of other gases . Air also contains a variable amount of water vapor . Except for the water vapor content, the composition of the troposphere is essentially uniform . The source of water vapor is at the Earth's surface through the process of evaporation . The temperature of the troposphere decreases with altitude . And, saturation vapor pressure decreases strongly as temperature drops . Hence, the amount of water vapor that can exist in the atmosphere decreases strongly with altitude and the proportion of water vapor is normally greatest near the surface of the Earth . </P> <P> The pressure of the atmosphere is maximum at sea level and decreases with altitude . This is because the atmosphere is very nearly in hydrostatic equilibrium so that the pressure is equal to the weight of air above a given point . The change in pressure with altitude can be equated to the density with the hydrostatic equation </P> <Dl> <Dd> d P d z = − ρ g n = − m P g n R T (\ displaystyle (\ frac (dP) (dz)) = - \ rho g_ (n) = - (\ frac (mPg_ (n)) (RT))) </Dd> </Dl>

In the troposphere which of the following does not decrease as altitude increases