Which gas is most important for understanding atmospheric processes? carbon dioxide oxygen water vapor ozone

Gases that trap heat in the atmosphere; these include water vapor, carbon dioxide, methane and ozone.

Water wapor is the most important gas for understanding atmospheric processes

Explanation:

To understand this you have to know that we have atmospherics processes such as radiation, aeroesol movement (this one is important to the process related with water cycles and energy) and convection. Water vapor plays an important role, this because transports latent heat also can condense into clouds and clouds reflects and adsorb solar radiation and affects earth's energy cycle, after that water vapor can be blown by the wind and return to the earth as snow or rain. Another process that is involved is that the heat radiated from the earth's surface is absorbed by the molecules of water vapor and they radiate heat in all directions. Finally water vapor is considered the second source of warmth to the earth.