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Given the same amount of water vapor, there will be a higher relative humidity in cool. It is affected by both temperature and pressure. The higher the percentage, the higher the humidity. Therefore, when ice is present, saturation occurs at a relative humidity of less than 100 %rh. Relative humidity compares the current ratio of absolute humidity to the maximum humidity for a given temperature and expresses this value as a percentage. As already noted, ice produces a lower vapor pressure than liquid water. Consequently, it is generally accepted that this type of sensor indicates relative humidity with respect to water at all temperatures (including below freezing). Relative humidity sensors are usually calibrated at normal room temperature (well above freezing). If the dry and wet bulb temperatures are set to the same value the calculator will show the saturation mixing ratio the amount of water in saturated air at that temperature. Where p is the actual partial pressure of the water vapor present in the ambient and p s the saturation pressure of water at the temperature of the ambient. If the air is fully saturated (100 relative humidity) the water cannot evaporate, so both the wet and dry bulb temperatures are the same. Relative humidity is the ratio of two pressures: V = volume occupied by the air – water vapor mixture N a = number of moles of dry air present in the volume V N w = number of moles of water vapor present in the volume V

Specific humidity is the ratio of the mass Mw of water vapor to the mass (Mw + Ma). M a = n a x m a = m a x pa V / RT = m a x (Pb – p) V / RT, where: The value of Dv can be derived as follows from the equation PV nRT. The mixing ratio r of moist air is the ratio of the mass M w of water vapor to the mass M a of dry air with which the water vapor is associated: Ratio of mass of water vapour at saturation to mass of dry gas. Z mix is the compression factor of the mixed gas system. Ratio of the mass of water vapour to the volume in which the humid gas is contained. Specific humidity is the ratio of the mass M w of water vapor to the mass (M w + M a) of moist air. Humidity calculator for conversion of humidity measurements.