Editing Humidity (section)

=== Absolute humidity ===

Absolute humidity is the total mass of water vapor (gas form of water) present in a given volume or mass of air. It does not take temperature into consideration. Absolute humidity in the atmosphere ranges from near zero to roughly {{cvt|30|g}} per cubic metre when the air is saturated at {{cvt|30|°C}}.<ref>{{cite web|title=Climate – Humidity indexes|url=https://www.britannica.com/science/climate-meteorology/Humidity-indexes|website=Encyclopaedia Britannica|access-date=15 February 2018|archive-date=16 November 2020|archive-url=https://web.archive.org/web/20201116162949/https://www.britannica.com/science/climate-meteorology/Humidity-indexes|url-status=live}}</ref><ref>{{cite web|title=Climate/humidity table|url=http://www.tis-gdv.de/tis_e/misc/klima.htm|website=Transport Information Service of the German Insurance Association|access-date=15 February 2018|archive-date=12 November 2020|archive-url=https://web.archive.org/web/20201112031304/https://www.tis-gdv.de/tis_e/misc/klima.htm/|url-status=live}}</ref>

Air is a gas, and its volume varies with pressure and temperature, per [[Boyle's law]].  ''Absolute humidity'' is defined as water mass per volume of air.  A given mass of air will grow or shrink as the temperature or pressure varies. So the absolute humidity of a mass of air will vary due to changes in temperature or pressure, even when the proportion of water in that mass of air (its ''[[#Specific humidity|specific humidity]]'') remains constant.  This makes the term ''absolute humidity'' as defined not ideal for some situations. 

Absolute humidity is the mass of the water vapor <math> (m_{\text{H}_2\text{O}}) </math>, divided by the volume of the air and water vapor mixture <math> (V_\text{net} )</math>, which can be expressed as:
<math display="block"> AH = \frac{m_{\text{H}_2\text{O}}}{V_\text{net}}. </math>  In the equation above, if the volume is not set, the absolute humidity varies with changes in air temperature or pressure. Because of this variability, use of the term ''absolute humidity'' as defined is inappropriate for computations in chemical engineering, such as drying, where temperature variations might be significant. As a result, absolute humidity in chemical engineering may refer to mass of water vapor per unit mass of dry air, also known as the ''humidity ratio'' or ''mass mixing ratio'' (see "specific humidity" below), which is better suited for heat and mass balance calculations.{{cn|date=December 2024}}  Mass of water per unit volume as in the equation above is also defined as ''volumetric humidity''. Because of the potential confusion, [[British Standard]] BS 1339<ref name="BS1339">British Standard BS 1339 (revised), Humidity and Dewpoint, Parts 1–3 (2002–2007)</ref> suggests avoiding the term "absolute humidity". Units should always be carefully checked.  Many humidity charts are given in g/kg or kg/kg, but any mass units may be used.