In humid, tropical regions, what is the maximum approximate percentage that water vapor can constitute of the atmosphere's total volume?

Answer

4%

Water vapor (H2O) is highly variable, but in humid regions, it can account for up to 4% of the total atmospheric volume, displacing other gases.

In humid, tropical regions, what is the maximum approximate percentage that water vapor can constitute of the atmosphere's total volume?
atmosphereGasesabundance