The formula for estimating the mass of H2O vapor in 1 m^3 of air at +20°C is:
M = ρ x V x RH x MW
where M is the mass of H2O vapor, ρ is the density of air, V is the volume of air, RH is the relative humidity, and MW is the molecular weight of water.
The density of air at +20°C can be calculated using the ideal gas law:
ρ = (P x MW) / (R x T)
where P is the pressure, MW is the molecular weight of air, R is the gas constant, and T is the temperature in Kelvin.
The average relative humidity of air at +20°C varies depending on location and weather conditions, but it is generally around 50%.
Estimating the mass of H2O vapor in air is important for understanding and predicting weather patterns, as well as for various industrial and scientific applications such as air conditioning and drying processes.
Some factors that can affect the accuracy of estimating the mass of H2O vapor in air include changes in temperature, pressure, and humidity, as well as the presence of other gases and pollutants in the air.