Psychrometric constant

The psychrometric constant γ {displaystyle gamma } relates the partial pressure of water in air to the air temperature. This lets one interpolate actual vapor pressure from paired dry and wet thermometer bulb temperature readings. The psychrometric constant γ {displaystyle gamma } relates the partial pressure of water in air to the air temperature. This lets one interpolate actual vapor pressure from paired dry and wet thermometer bulb temperature readings. Both λ v {displaystyle lambda _{v}} and M W r a t i o {displaystyle MW_{ratio}} are constants.Since atmospheric pressure, P, depends upon altitude, so does γ {displaystyle gamma } .At higher altitude water evaporates and boils at lower temperature. Although ( c p ) H 2 O {displaystyle left(c_{p} ight)_{H_{2}O}} is constant, varied air composition results in varied ( c p ) a i r {displaystyle left(c_{p} ight)_{air}} .