The saturation vapor density (SVD) is the maximum density of water vapor in air at a given temperature. The concept is related to

saturation vapor pressure Vapor pressure (or vapour pressure in English-speaking countries other than the US; see spelling differences) or equilibrium vapor pressure is defined as the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases ...

(SVP). It can be used to calculate exact quantity of

water vapor (99.9839 °C) , - , Boiling point , , - , specific gas constant , 461.5 J/( kg·K) , - , Heat of vaporization , 2.27 MJ/kg , - , Heat capacity , 1.864 kJ/(kg·K) Water vapor, water vapour or aqueous vapor is the gaseous pha ...

in the air from a

relative humidity Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation, dew, or fog to be present. Humidity depe ...

(RH = % local air humidity measured / local total air humidity possible ) Given an RH percentage, the density of water in the air is given by . Alternatively, RH can be found by . 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 The ideal gas law, also called the general gas equation, is the equation of state of a hypothetical ideal gas. It is a good approximation of the behavior of many gases under many conditions, although it has several limitations. It was first stat ...

: where is the SVP, is the volume, is the number of

moles Moles can refer to: * Moles de Xert, a mountain range in the Baix Maestrat comarca, Valencian Community, Spain * The Moles (Australian band) *The Moles, alter ego of Scottish band Simon Dupree and the Big Sound People *Abraham Moles, French engin ...

, is the

gas constant The molar gas constant (also known as the gas constant, universal gas constant, or ideal gas constant) is denoted by the symbol or . It is the molar equivalent to the Boltzmann constant, expressed in units of energy per temperature increment per ...

and is the temperature in

kelvin The kelvin, symbol K, is the primary unit of temperature in the International System of Units (SI), used alongside its prefixed forms and the degree Celsius. It is named after the Belfast-born and University of Glasgow-based engineer and phys ...

s. The number of moles is related to density by , where is the mass of water present and is the molar mass of water (18.01528 grams/mole). Thus, setting to 1 cubic meter, we get = = density. The values shown at hyperphysics-sources 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). Therefore, for particular mole number and volume the saturated vapor pressure will not change if the temperature remains constant.

References

{{Reflist Atmospheric thermodynamics Thermodynamic properties