Editing Dew point (section)

==Humidity==
If all the other factors influencing humidity remain constant, at ground level the [[relative humidity]] rises as the temperature falls; this is because the air's capacity to hold water vapor decreases, and less vapor is needed to saturate the air. The dew point temperature equals the air temperature when the air is saturated with water; in all other cases the dew point will be less than the air temperature.<ref>{{Cite book |last=Spiridonov |first=Vlado |url=https://link.springer.com/10.1007/978-3-030-52655-9 |title=Fundamentals of Meteorology |last2=Ćurić |first2=Mladjen |date=2021 |publisher=Springer International Publishing |isbn=978-3-030-52654-2 |location=Cham |language=en |doi=10.1007/978-3-030-52655-9}}</ref>{{rp|129}} 

In technical terms, the dew point is the temperature at which the water vapor in a sample of [[air]] at constant [[barometric pressure]] condenses into liquid water at the same [[reaction rate|rate]] at which it evaporates.<ref>{{Cite Merriam-Webster|dew point}}</ref> At temperatures below the dew point, the rate of condensation will be greater than that of evaporation, forming more liquid water. The condensed water is called [[dew]] when it forms on a solid surface, or [[frost]] if it freezes.  In the air, the condensed water is called either [[fog]] or a [[cloud]], depending on its altitude when it forms.  If the temperature is below the dew point, and no dew or fog forms, the vapor is called [[supersaturated]]. This can happen if there are not enough particles in the air to act as [[condensation nuclei]].<ref name=ctrib>{{cite news |last1= Skilling |first1=Tom|title=Ask Tom why: Is it possible for relative humidity to exceed 100 percent?|url= https://www.chicagotribune.com/2011/07/20/ask-tom-why-is-it-possible-for-relative-humidity-to-exceed-100-percent/ |access-date=24 January 2018|work=Chicago Tribune|date=20 July 2011}}</ref>

The dew point depends on how much water vapor the air contains. If the air is very dry and has few water molecules, the dew point is low and surfaces must be much cooler than the air for condensation to occur. If the air is very humid and contains many water molecules, the dew point is high and condensation can occur on surfaces that are only a few degrees cooler than the air.<ref>{{Cite book |title=Moisture Control Guidance for Building Design, Construction and Maintenance |publisher=U.S. Environmental Protection Agency }}</ref>

A high relative humidity implies that the dew point is close to the current air temperature. A relative humidity of 100% indicates the dew point is equal to the current temperature and that the air is maximally saturated with water. When the moisture content remains constant and temperature increases, relative humidity decreases, but the dew point remains constant.<ref name=Horstmeyer>{{cite web| last=Horstmeyer | first=Steve | title=Relative Humidity....Relative to What? The Dew Point Temperature...a better approach | publisher=Steve Horstmeyer | date=2006-08-15 | url=http://www.shorstmeyer.com/wxfaqs/humidity/humidity.html| access-date=2009-08-20}}</ref>

[[General aviation]] pilots use dew point data to calculate the likelihood of [[carburetor icing]] and [[fog]], and to estimate the height of a [[cumuliform]] [[cloud base]].

Increasing the barometric pressure raises the dew point.<ref>{{cite web|title=Dew Point in Compressed Air – Frequently Asked Questions|url=https://www.vaisala.com/sites/default/files/documents/Dew-point-compressed-air-Application-note-B210991EN-B-LOW-v1.pdf|website=Vaisala|access-date=15 February 2018|archive-date=16 February 2018|archive-url=https://web.archive.org/web/20180216030042/https://www.vaisala.com/sites/default/files/documents/Dew-point-compressed-air-Application-note-B210991EN-B-LOW-v1.pdf|url-status=dead}}</ref> This means that, if the pressure increases, the mass of water vapor per volume unit of air must be reduced in order to maintain the same dew point. For example, consider New York City ({{convert|33|ft|m|abbr=on|disp=or}} elevation) and Denver ({{convert|5280|ft|m|abbr=on|disp=or}} elevation<ref name="denfacts">{{cite web|url=http://www.denvergov.org/AboutDenver/today_factsguide.asp |title=Denver Facts Guide&nbsp;– Today |publisher=The City and County of Denver |access-date=March 19, 2007 |url-status=dead |archive-url=https://web.archive.org/web/20070203182736/http://www.denvergov.org/AboutDenver/today_factsguide.asp |archive-date=February 3, 2007 }}</ref>). Because Denver is at a higher elevation than New York, it will tend to have a lower barometric pressure. This means that if the dew point and temperature in both cities are the same, the amount of water vapor in the air will be greater in Denver.