Relative humidity<span> (</span>RH<span>) is the ratio of the </span>partial pressure<span> of water vapor to the </span>equilibrium vapor pressure<span> of water at a given temperature. Relative humidity depends on temperature and the pressure of the system of interest. It requires less water vapor to attain high relative humidity at low temperatures; more water vapor is required to attain high relative humidity in warm or hot air.</span>
