Saturation vapor density
The saturation vapor density (SVD) is the maximum density of water vapor in air at a given temperature.[1] The concept is related to saturation vapor pressure (SVP). It can be used to calculate exact quantity of water vapor in the air from a relative humidity (RH = % local air humidity measured / local total air humidity possible ) Given an RH percentage, the density of water in the air is given by RH × SVD = Actual Vapor DensityScript error: No such module "Check for unknown parameters".. Alternatively, RH can be found by RH = Actual Vapor Density / SVDScript error: No such module "Check for unknown parameters".. As relative humidity is a dimensionless quantity (often expressed in terms of a percentage), vapor density can be stated in units of grams or kilograms per cubic meter.
For low temperatures (below approximately 400 K), SVD can be approximated from the SVP by the ideal gas law: P V = n R T Script error: No such module "Check for unknown parameters". where Template:Mvar is the SVP, Template:Mvar is the volume, Template:Mvar is the number of moles, Template:Mvar is the gas constant and Template:Mvar is the temperature in kelvins. The number of moles is related to density by n = m / MScript error: No such module "Check for unknown parameters"., where Template:Mvar is the mass of water present and Template:Mvar is the molar mass of waterScript error: No such module "Unsubst". (18.01528 grams/mole). Thus, we get Template:Sfrac = Template:Sfrac = density.
The values shown at hyperphysics-sources[2] indicate that the saturated vapor density is 4.85 g/m3 at 273 K, at which the saturated vapor pressure is 4.58 mm of Hg or 610.616447 Pa (760 mm of Hg ≈ 1 atm = 1.01325 * 105 Pa).
References
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