Question

How would I convert relative humidity to specific humidity? The variables I have are vapor pressure, air temperature, and relative humidity.

Answer 1

We know that

Relative humidity can be defined as the ratio of vapour pressure of water (at a temperature and pressure) to the vapour pressure of gas over water φ = p_w / p_ws 100%

specific humidity can be defined as the ratio of the mass of water vapor in air to the total mass of the air ans water vapour x_s = 0.622 p_ws / (p_a - p_ws)   

Where

φ = relative humidity

x_s = specific humidity of air vapor mixture (kg/kg)

ρ_ws = density of water vapor

ρ = density of the moist or humid air

we have air temperature , vapour pressure and relative humidity

φ = p_w / p_ws

x_s = 0.62 p_ws / (p_a - p_ws)   

so on rearranging we may say that

x_s = 0.62 φ ρ_ws / (ρ - ρ_ws)