Talk:Water vapor

To upgrade Classification to "A" status
Article needs to be well written, reasonably complete and referenced; possible featured article candidate. Moslty, this may be true, however, references may need the most attention. -- Hard Raspy Sci 02:52, 1 December 2006 (UTC)


 * Actually this comment is outdated, the next step is "GA" status...see status comments below.—Will research for food (talk) 16:13, 19 November 2009 (UTC)

Footnotes and References added
I added the references I had, but I think other major contributors may have more... Also, I put notes out of the main article and into the notes/refs section. -- Hard Raspy Sci 20:29, 15 December 2006 (UTC)

I think so too. 24.11.7.108 00:18, 7 March 2007 (UTC)Kat


 * Still needs more references. —Will research for food (talk) 18:27, 23 November 2009 (UTC)

Suggestion of merge from steam
See discussion at Talk:Steam. Nurg 04:41, 24 February 2007 (UTC)

Since there is actually no discussion of a merge there, or here, I assume that this suggestion of merge is a joke, and have removed reference to it from the article. --75.49.222.55 03:50, 9 October 2007 (UTC)


 * No merge. —Will research for food (talk) 18:28, 23 November 2009 (UTC)

Bad wording
This sentence under "General Discussion" needs a complete overhaul: "Dew point temperature and relative humidity act as guidelines for the process of water vapor in the water cycle." As written, it's just about meaningless. Lincmad 19:48, 28 February 2007 (UTC)


 * I agree somewhat...however it reads more like cliff notes for a physicist. It has too much meaning in too few words, and needs to be expanded.  — HRS IAM 02:39, 30 July 2007 (UTC)

Flammability
Is water vapor flammable? There's an oxidizer (oxygen) and a fuel (hydrogen), why isn't there at least some information as to whether or not there's a temperature at which water vapor is flammable? James Callahan 00:51, 15 April 2007 (UTC)
 * Because the hydrogen has already been oxydized? Carbon is flammable in an oxygen atmosphere, but carbon dioxide is not flammable.  (SEWilco 02:09, 15 April 2007 (UTC))
 * That makes sense, thank you. Any chance this could be added to the article? James Callahan 04:29, 18 April 2007 (UTC)
 * No, because oxy[---] does not mean flammable or not. Sorry, that is beyond the scope of the article. - HRS IAM 01:53, 30 July 2007 (UTC)

Extraterrestrial water vapor

 * There are some problems with the discussion of extraterrestrial water vapor -- _some_ of the water at Mars' polar caps sublimates in the summer, but the vast majority of it is perennial. I think the person who wrote this before was getting it confused with CO2, which sublimates completely from the NP of Mars in summer. — [previously unsigned by anonymous IP, and badly placed originally on 18:08, 15 February 2007 by User:128.148.116.135 ]


 * Not really, I read the article, its more about what the original hypothesizes and not what you are saying. Other than that, I don't know what you are referring to. — HRS IAM 02:33, 30 July 2007 (UTC)


 * This subpart needs to be its own subheading. —Will research for food (talk) 18:30, 23 November 2009 (UTC)

Lightning Generation
Most or all of what was written about the role of water vapor in lightning generation appears to me to have been written by someone with no actual knowledge of the process of thunderstorm electrification. Many statements are either questionable or simply irrelevant. In particular, reference is made to the insulating properties of water vapor, when in fact water vapor is a poorer insulator than dry air. I would argue that the connection between water vapor and lightning generation is sufficiently indirect as to not warrant a section in this article at all. Rather it is appropriate to address the role of water vapor, and of latent heat release due to phase changes, in the occurrence of deep convective cloud systems, while the occurrence of lightning in those cloud systems is far more directly related to the process of precipitation formation. My instinct is to simply delete the section in question rather than to take the effort to massage it into something correct and useful, but I'll defer until there's been an opportunity for comments. Gpetty (talk) 18:22, 27 November 2007 (UTC)


 * Yes, please discuss the finer points you are not clear about. I already see that this section needs some expanding to qualify for wide-readership.—Will research for food (talk) 17:15, 19 November 2009 (UTC)


 * I agree with this observation. In fact, the person who wrote this has several misconceptions. It is stated that static discharge is quick and easy in dry air. This is based on the misconception that dry air is a conductor of electricity. It is precisely the opposite. Static charge builds up more easily in dry air because it is not conducted away. In humid air, the charge is conducted away before it builds up to a high enough voltage to cause a noticeable spark.Rocket Laser Man (talk) 23:39, 15 November 2010 (UTC)


 * Likewise, in discussing lightning, several statements are wrong, because they are based on this same misconception.Rocket Laser Man (talk) 23:38, 15 November 2010 (UTC)

PLEA TO SENIOR EDITORS
as of 17March2008> WikiProject-Chemistry, WikiProject-Physics and WikiProject-Meteorology EACH rate this article at "mid-importance" -surely this makes a CUMULATIVE HIGH IMPORTANCE for this article !!!''' —Preceding unsigned comment added by 80.42.201.58 (talk) 05:36, 17 March 2008 (UTC)


 * I believe this is rated as High importance for Meteorology, and mid- for the others, which is probably ok. However, Physics and Chemistry has been used heavily to clarify many issues. —Will research for food (talk) 17:20, 19 November 2009 (UTC)

Misleading image
While I'm sure the locale pictured in File:St_Johns_Fog.jpg did indeed contain water vapor, it isn't visible. All that appears in the (admittedly lovely) image is liquid water in the river and suspended in the air as fog. There is already widespread confusion about "steam" being visible, so leading off this article about an invisible gas with an image of visible water seems... unwise. Perhaps an image of a whistling tea kettle, so that the contrast between the actual vapor and the mist can be pointed out? --Steve-o Stonebraker (talk) 20:42, 27 January 2009 (UTC)
 * I completely agree. Water vapor is an invisible gas, so showing a picture of fog is misleading. Spiel496 (talk) 16:24, 10 March 2009 (UTC)
 * Agree, as well, its misleading to use fog or a steam system (open or closed) as an example. The best bet is to try to acquire a pair of photos with an object in the far background under two different atmospheric conditions--ie. dry day vs. humid day.  Water vapor over long distances is visible, but not nearly as visible as clouds, steam, or fog. Will research for food (talk) 07:05, 19 November 2009 (UTC)


 * There should have been a satellite link that addresses this issue by example as well ... —Will research for food (talk) 17:22, 19 November 2009 (UTC)

SEEKING SUPPORT for reinstatement of a sub-section that originally existed for the entire duration of 2008
79.76.195.166 (talk) 17:15, 12 February 2009 (UTC) {|width="95%" border="1" cellpadding="2" cellspacing="0"

Scientific Discrepancies, Confounding factors and limits of knowledge
Since water vapor is very common, it has been studied and written about from many perspectives. As working knowledge has grown and developed within apparently unrelated fields several discrepancies in understanding may be encountered. These discrepancies often arise from an inability to rigidly determine either a volumetric or gravimetric basis of study; and/or use of constants inappropriate for the conditions being observed.

Many scientific studies view water vapor as a Confounding variable (preventing Ceteris paribus, also 'lurking variable') due to its complex nature; this becomes especially true when the study observes significant variation in water vapor quantities, over time and/or location.

It is for the reasons above that this remains a particularly tricky and sometimes controversial factor in many fields of science, whether storage of foods or ancient artefacts, thermodynamics or climate change.
 * }
 * The above section survived over 400 days and 195 edits,
 * but has now been crudely edited (removed entirely on three occasions) by three editors.

Evidence to support the inclusion are... Comments...
 * the many companies providing equipment and calibration involved in the metrology of water vapor
 * the many industries attempting to manage changes in water vapor within their processes/services
 * the many academic papers attempting to elucidate the boundaries of existing knowledge

I know nothing about this subject, though I have experience in writing articles, and I did add the FAB image in the infobox at the top. Regardless of how long the information has lasted, it should be cited to reliable sources. I don't know if it is being removed for inaccuracy or just for the fact that it's not cited, or for some other reason, but the first action to be taken is full citations. If you need help with the wiki code and citations, let me know. --Moni3 (talk) 17:39, 12 February 2009 (UTC)

Let me add please that the editors who are removing and replacing the information are in danger of edit warring. The discussion on the talk page is the way to go to get around this. There is no quibbling about edit warring. Any editor will be blocked for doing it. --Moni3 (talk) 17:43, 12 February 2009 (UTC)


 * It's uncited, and it's gobbledegook. What is is supposed to mean? It should certainly remain out until fixed up William M. Connolley (talk) 18:34, 12 February 2009 (UTC)
 * I second it, uncited and gives no positive worth to the article...In fact this type of speech has been deleted from this article numerous times in the past for its excessive vagueness. It is of no use to mystify "water vapor". Will research for food (talk) 07:08, 19 November 2009 (UTC)

Section to be excluded--Reasons: vague, uncited, or already covered by the article
The above section, as written is a stub article. Water vapor, as currently written, is already beyond this section and already addresses issues contained in the section. Yes, it is true water vapor is an extremely difficult subject matter to address. If anyone feels that some finer points are not covered by the article, please place those comments in talk as we are attempting to take this article to the next step, then those concerns will be appropriately addressed in this forum.

Discussion:
The section will remain deleted as it is not "GA status" material. Any further arguments should be listed here, and must contain valid citations. Re-wording of the section is not applicable, as it repeats material already covered by the article. If no discussions follow this after 2 weeks, the decision will remain final as consensus. —Will research for food (talk) 17:03, 19 November 2009 (UTC)


 * No discussion has occured to support the above article, up to the time of this posting, so by consensus it remains deleted. —Will research for food (talk) 15:20, 22 January 2010 (UTC)

global warming
why has the fox news told me water vapor is the major greenhouse gas? is this true? —Preceding unsigned comment added by 70.160.101.190 (talk) 19:02, 10 May 2009 (UTC)


 * Yes, it is the major greenhouse gas. Q Science (talk) 07:41, 11 May 2009 (UTC)


 * Correct. —Will research for food (talk) 18:32, 23 November 2009 (UTC)

IR absorption
Dry air is transparent to infrared while moist air is absorbent of  IR. This fact is important in weather production and should be mentioned.Water Vapor is very interesting.

Arydberg (talk) 20:25, 29 August 2009 (UTC)


 * Interesting point for several reasons, dry air is mostly Nitrogen and Oxygen. But, also, moist air, is also absorbent of a broadband of EM radiation as well..refractive, reflective, etc...see one of the notes concerning radar on the main page. Will research for food (talk) 07:14, 19 November 2009 (UTC)


 * Also, forgive the double post, IR spectrum is used already by Weather Satellites to identify areas of water vapor in the atmosphere... See GOES ... and as a matter of fact there used to be a link to an example of this on the main page. -- Will research for food (talk) 07:49, 19 November 2009 (UTC)


 * Dry air is not transparent to IR. It contains CO2, methane, ozone, and other radiatively active gases. Short Brigade Harvester Boris (talk) 00:19, 20 November 2009 (UTC)


 * Ok, lets stop this one, please review the full spectrum analysis of Earth's atmosphere before proceeding. Air's level of transparency is directly related to the frequency of the specific EM transmission.


 * Dry air is the least 'reactive' to EM radiation, so therefore it is largely transparent to most of the IR spectrum. It just so happens that our atmosphere is most transparent to visible light. —Will research for food (talk) 04:32, 22 November 2009 (UTC)


 * OK, looks like we've got crosstalk between two topics, radar and IR. Short Brigade Harvester Boris (talk) 15:45, 22 November 2009 (UTC)


 * Nope, the references include full spectrum analysis. Only 2 of the books have "radar" in their title, but they both deal with remote sensing and LIDAR...which also includes the IR band as well. The other is an EM signals variety, it also includes the full spectrum analysis.  These are a few amongst a ton of remote sensing and antenna design books/journals, and are 3 that I know are readily available at most libraries for people to peruse. —Will research for food (talk) 14:37, 23 November 2009 (UTC)


 * So the statement "Dry air is not transparent to IR." is a false statement. Otherwise this would not be possible...see Satellite Image Comparison. —Will research for food (talk) 14:47, 23 November 2009 (UTC)


 * Please go read greenhouse gas. Short Brigade Harvester Boris (talk) 15:04, 23 November 2009 (UTC)


 * More explicitly, please see this image which clearly shows that some frequencies are blocked and that others are transparent. Q Science (talk) 17:46, 23 November 2009 (UTC)


 * Ok, first, thank you for the reference, it helps. Second, I can address the issue more clearly.  Actually, thanks for both references (article and image).  The Image is correct, while the article "greenhouse gas" is incorrect.  GHG discussions are usually screwed up.  For instance the first lines of the article, GHG, is a false statement and needs to be fixed. (I will tackle GHG next.)


 * Now compare what the Image is telling us and what the article says in the first two sentences. They don't "jive". Really the article should say or be more general by saying something like:


 * GHG's are broad spectrum absorbers of light energy from the sun (see this image)...as a result of molecular degrees of freedom of each variety of GHG, they each, disproportionately, aid in the subsequent green house effect. The green house effect should not be seen as a bad effect.......


 * I don't subscribe to the sky is falling attitude. But please understand that "water vapor" holds an extremely difficult to understand role in our atmosphere, a terribly complex factor in many seemingly unrelated ways. Many people for no reason, other than fright factor, would readily believe that carbon dioxide was the major GHG, when water vapor is the most significant player.  Water vapor has the major control in environmental factors, CO2 is a minor player.


 * Ok, that part was beside the point. The question here is about IR. The significant gases in our atmosphere play THE role in what lives on the surface of the planet. WHY? By perusing the graphic we see that not all frequencies are as readily transmitted by our "air".  The visible spectrum is the least blocked, while others are more blocked, but NOT entirely blocked. Very key point here.  Otherwise we would fry due to UV radiation.  Also, please understand that all light (photon) energy is energy and can be converted to heat...I repeat ALL light.  The statement that only IR is responsible for heating is false, but not exclusive. —Will research for food (talk) 18:59, 23 November 2009 (UTC)

There is almost no such thing as dry air where "warming" is important. In the driest desert water vapor is 6x more prevalent than CO2. Only in regions that are usually below zero, is the air really "dry." Oceans, 70% of the world, of course are 100% humidity, the average temperature of the Earth, 19C corresponds to 18000 ppm, or 45x more common than CO2. Of course WV is roughly 40x more active than CO2 as well, it's spectra has 2 wide peaks, and never really goes to zero in the IR. This means concentration effects, relative to CO2 are monstrous.GESICC (talk) 03:47, 20 February 2015 (UTC)

Water Clusters
I really think someone with more knowledge than me should mention something about water clusters; little groupings of water molecules floating around in the air. Seams to fit the water vapor definition pretty well ;) 79.76.178.241 (talk) 16:10, 27 October 2009 (UTC)


 * Interesting, however, it seems that the article talks about clusters in solids, it may be out of the scope of this article, but could warrant a link to water clusters. —Will research for food (talk) 14:59, 19 November 2009 (UTC)


 * article here about Atmospheric Water Clusters > http://www.sciencedaily.com/releases/2004/02/040225073100.htm —Preceding unsigned comment added by 79.67.115.178 (talk) 12:48, 22 February 2010 (UTC)

Metal is NOT waterproof !??
http://www.ima.co.uk/technical/transpiration.pdf

The link above has an article that states that water can pass through plastic and metal, if this is true it would be an excellent fact to include in this wiki article.79.76.155.85 (talk) 08:54, 2 November 2009 (UTC)
 * I am sorry, but I don't think that argument holds water. Will research for food (talk) 07:22, 19 November 2009 (UTC)


 * here's a little moisture for anyone who missed that dry humor 79.67.115.178 (talk) 13:20, 22 February 2010 (UTC)

Debunked
I read the article, it is not a valid source article. While the article claims many 'sciency' factoids, it has no references itself and is one that merely expresses business interests, not true facts. Its classification is internet junk source. —Will research for food (talk) 16:28, 19 November 2009 (UTC)

This article is very much junk, as water vapor is composed of small droplets of LIQUID water suspended in the air. The gaseous phase of water is steam. How in the world can Wikipedia have such a laughable article calling water vapor a gas???130.111.163.179 (talk) 03:07, 21 June 2010 (UTC) suma rongi. cast aluminium is permeable to both water and cooking oils. We had in our lab someone's attempt at Cast aluminium fishing floats for deep sea use. They filled with water when dragged under. (Don't know how deep). And the black gunge on the base of a cast aluminium frypan is oils/fat that has migrated through the casting/spun aluminium. [BTW we used a Palladium leak in our van der Graaf accelerator, between the gas cylinder source, and the Belt of the machine. This Pa was heated gently to allow more H through the Pa. So some metals are permeable to gas as well. All part ofthe erason for the use of the Pt group for H catalysis.Suma rongi (talk) 06:57, 30 May 2011 (UTC)]

Water vapour is a gas; it is the gaseous phase of water. Steam consists of small droplets of liquid water suspended in air. That is why steam is visible, while water vapour is not. (124.168.202.62 (talk) 14:32, 28 January 2012 (UTC))


 * "Water vapour is a gas; it is the gaseous phase of water. Steam consists of small droplets of liquid water suspended in air. That is why steam is visible, while water vapour is not."
 * We were taught exactly the opposite in my high school chemistry class.
 * Vapor is mist and can be visible. Steam is clear and is the gaseous phase of water above the boiling point. It will burn you on contact. It has a lot of energy because of the phase change, which vapor does not.

See https://en.wikipedia.org/wiki/Steam "Steam is water in the gas phase."
 * There is some confusion between the scientific and the colloquial uses of the terms steam and vapor. It doesn't help that water vapor (not steam) is classed as a "greenhouse gas" along with actual gases like CO2 and methane. So we have NASA leading off with "Water vapor is Earth’s most abundant greenhouse gas." https://science.nasa.gov/earth/climate-change/steamy-relationships-how-atmospheric-water-vapor-amplifies-earths-greenhouse-effect/
 * There may also be some dumbing down of the level of STEM knowledge in our society since I went to school.

In chem class we were taught that elements have three phases, solid, liquid and gas, and also some hybrid states like solutions, gels, suspensions and mixtures. I guess vapor is kind of a suspension of very small liquid droplets in a gas. It helps to keep the phase concept in mind when using scientific instead of kitchen terminology for vapor and steam.
 * There is a lot of confusion about this from apparently authoritative sources like Energy Education or Physics Stack Exchange. Maybe the truth is more complicated.
 * This article includes some expert technical topics from people who know a lot more about it. It would be great if someone qualified like that could clear up the conflict here about what is vapor and what is steam.
 * I landed here looking for an explanation why water vapor is sometimes invisible and sometimes visible as clouds. According to http://ed-web3.educ.msu.edu/reports/matter-molecules/Sciencestu/scistu1.pdf it can exist as individual molecules of water moving freely like a gas. So maybe water can behave like a gas when it's suspended in gases like O2 and N2.

JPLeonard (talk) 21:42, 24 April 2024 (UTC)

Next level - GA status
The 6 B status requirements seem to be fulfilled at this time. Discussion to outline needed requirements for GA. —Will research for food (talk) 17:08, 19 November 2009 (UTC)

Graph and Empirical Formula
The graph of "saturation fraction of water in air at sea level" should have units on the y axis. I'm not sure if that's mass fraction or mole fraction. I guess its probably mass, but I'm not sure. Also, does the red line have an empirical formula; including that would make it more practically useful.

Also regarding the empirical formula listed in the "general discussion" section: do the other formulas mentioned have their own pages? If so it would be good to include links.

I'll try to find the formulas myself, but I'm new to this subject. Michael ages (talk) 20:27, 17 December 2010 (UTC)

The annual mean global concentration?
From the article: "The annual mean global concentration of water vapor would yield about 25 mm of liquid water over the entire surface of the Earth if it were to instantly fall as rain." This looks strange to me.

What is an annual concentration!?

Shouldn't it rather be "The total content of water vapor in the atmosphere would yield about 25 mm of liquid water over the entire surface of the Earth if it were to instantly fall as rain."!?Krille Katalog (talk) 05:19, 14 May 2011 (UTC)
 * Not if the total water vapor content in the atmosphere is variable. --Kim D. Petersen (talk) 14:44, 28 January 2012 (UTC)


 * Your remark is correct. I made some changes, with some edit conflict with another editor. Sorry 'bout that!. Accident.  JonRichfield (talk) 17:29, 28 January 2012 (UTC)

Non-specific heat
I notice that someone wanted a citation for SH of steam at given pressure. I reverted to my ancient steam-driven handbook of chem and phys (1966) and got a table that I could calculate with on my ancient steam-driven calculator (1990s) and got values from 19xx to 26xx, or thereabouts. I had intended giving one value, but: I don't know which value would make most sense; and to give a range would be a bit complicated, given the number of variables and considerations. SO, therefore, I boldly elect to remove the entry, which now looks nonsensical in its current form. I await equally bold correction with anticipation and equanimity, hoping that someone has something constructive to replace it with. JonRichfield (talk) 12:45, 19 March 2012 (UTC)

'Aqueous vapor'
Is it really worth including 'aqueous vapor' at the beginning of this entry, as if this were a common name for the substance? I make it about 1/300 as common as 'water vapor'. I'm not sure anyone's used it since the 1880s. --Oolong (talk) 16:54, 28 October 2013 (UTC)

Orphaned references in Water vapor
I check pages listed in Category:Pages with incorrect ref formatting to try to fix reference errors. One of the things I do is look for content for orphaned references in wikilinked articles. I have found content for some of Water vapor's orphans, the problem is that I found more than one version. I can't determine which (if any) is correct for this article, so I am asking for a sentient editor to look it over and copy the correct ref content into this article.

Reference named "NASA-20131212-EU": From Europa (moon):  From Extraterrestrial liquid water:  

I apologize if any of the above are effectively identical; I am just a simple computer program, so I can't determine whether minor differences are significant or not. AnomieBOT ⚡ 08:48, 15 December 2013 (UTC)
 * ✅ - updated reference and related - enjoy! :) Drbogdan (talk) 09:48, 15 December 2013 (UTC)

Remove uncited global warming fallacy
I suggest "Because the water vapor content of the atmosphere will increase in response to warmer temperatures, there is a water vapor feedback which is expected to amplify the climate warming effect due to increased carbon dioxide alone." Be removed. It has never been cited and this is not how feedback works. If CO2 causes more liberation of water vapor (135ppm drives 435 ppm), then the 435 ppm should drive an additional effect. Water vapor being a much more powerful driver. By way of understand, imagine they are equivalent drivers of feedback. There are arguments that evaporation/condensation places a governor on water vapor, but this would have the same effect on CO2, of course-water vapor green house effects may be viewed as an independent phenomenon from evaporation condensation.GESICC (talk) 03:59, 20 February 2015 (UTC)
 * I'll second that. Also, the statement ""Conversely, adding water vapor at high altitudes has a disproportionate impact, which is why methane .. and jet traffic have disproportionately high warming effects." offers some cites regarding contrails but cannot offer any regarding methane. Since the stratosphere is relatively cold, this postulate seems counterintuitive and therefore demands verification. --Anteaus (talk) 15:39, 14 February 2016 (UTC)

Calculations - density of water vapor
"Using Avogadro's Law and the ideal gas law, water vapor and air will have a molar volume of 22.414 L/mol at STP. A molar mass of air and water vapor occupy the same volume of 22.414 litres. The density (mass/volume) of water vapor is 0.804 g/L"

Would a clarifying statement be useful, to distinguish the "density of water vapor" calculated here from the saturation vapor density (a quantity that is about 2 orders of magnitude smaller)? --129.31.246.50 (talk) 10:57, 11 April 2016 (UTC)

Assessment comment
Substituted at 10:18, 30 April 2016 (UTC)

Water Vapor - clarify Definition please
Rather than directly edit this page I think it important to get clarity on definitions.

I was always taught that :

Water vapor is a suspension of very small sub-boiling water droplets in air; it is often visible when the concentration is high enough, and that Steam is actually water in it's gaseous form (i.e.individual water molecules moving independently of each other).

Steam will often condense first into Water vapor, before further condensing into liquid water (especially when coming into contact with a cold surface or cold air).

I was also taught that when you see a kettle boil, than above the spout that there is a small gap before the visible cloud can be seen. This visible cloud is mistakenly called Steam but it is actually Water Vapor (i.e. the droplets). The gap between the spout and the visible cloud is actually occupied by Steam - the invisible gaseous state of water - this is condensing quickly into visible water vapor as it exits the spout, as the ambient Temp outside the kettle is significantly below 100°C.

If I am wrong - what is the difference between water Vapor and steam (if any), and what is the name of the form of water that contains microscopic water droplets (i.e. not separate water molecules), — Preceding unsigned comment added by TonyFlury (talk • contribs) 10:42, 20 February 2017 (UTC)


 * Water vapor is simply water in the vapor phase. Just like iodine vapor is iodine in the vapor phase, alcohol vapor is alcohol in the vapor phase, etc., etc. A vapor is a gas that is below its critical point temperature. Water vapor is colorless, so it is invisible in air. If water vapor is cooled and condenses into tiny droplets then it becomes visible as a white 'cloud'. This is what you see when you breathe out on a cold day or when the hot water vapor from your kettle hits the colder air in the room. You might call this 'cloud' condensate; you could also call it an aerosol. In popular usage, people often use the word "steam" to refer to this cloud, though this is perhaps unhelpful. Engineers use the word steam to mean water vapor that has been produced by boiling water, so it generally means water vapor that is hot and/or under pressure.Dezaxa (talk) 10:29, 26 September 2017 (UTC)

Questionable mechanism of evaporative cooling
The article says "Liquid water that becomes water vapor takes a parcel of heat with it" as the mechanism of evaporative cooling. Isn't that backwards? The water molecule leaving the surface before encountering its first air molecule (about 70 picoseconds later) is extremely cold compared to even the coldest nearby air molecules because it has negligible energy in its three translational DOFs, and therefore takes a parcel of heat out of that air molecule (and a few more during the following nanosecond before reaching equipartition of energy among the nearby DOFs). That account yields the correct value for latent heat of vaporization by an easy calculation.

I don't see any calculation here that comes remotely close to the correct value. Unless someone can show otherwise by an actual calculation I submit that the article is simply wrong on this point. Vaughan Pratt (talk) 00:12, 19 April 2017 (UTC)
 * Just curious, but why are you only using the 3 translational degrees of freedom for your calculation? The equipartition theorem includes translational, rotational, and vibrational degrees of freedom equally. For water, that would be 9 degrees of freedom, not 3. --OuroborosCobra (talk) 15:13, 11 May 2020 (UTC)

In Earth's atmosphere
The claim that "The mean global content of water vapor in the atmosphere is roughly sufficient to cover the surface of the planet with a layer of liquid water about 25mm deep" calls for a citation. I found a reference here, drawing on data from ISCCP:

https://www.climate4you.com/ClimateAndClouds.htm#Clouds%20and%20atmospheric%20water%20vapour

I'll leave it to a more experienced wikipedia editor to decide if it is appropriate to include this reference in the page. George963 au (talk) 13:17, 11 May 2020 (UTC)


 * Thanks, potentially useful, although I believe the 'climate4you' site is associated with Ole Humlum and far from reliable. You can get the ISCCP NASA data the chart was based on from, and the 'plot' of deviations at the bottom gives mean for 1993-2009 of 2.41 cm ±0.17% - so fairly precise, but that project is concentrating on clouds and it's not clear it includes TPW above 310 mb.   --Cedderstk 08:14, 22 August 2021 (UTC)

Global mean of total column precipitable water vapour
I was looking online for the mean value for total precipitable water vapour (or for mixing ratio). Most online sources suggest around 25 mm. User:Nwbeeson helpfully added  a reference to Gleick in Encyclopedia of Climate and Weather for the paragraph of section 'In Earth's atmosphere' quantifying turnover, but reduced the value to:

"The mean global content of water vapor in the atmosphere is roughly sufficient to cover the surface of the planet with a layer of liquid water about 1 cm deep."

10 mm is notably lower than other online sources and compared to the '1 part in 100,000 of the total water on Earth'. A presentation by Forsythe et al has 'Global mean Total Precipitable Water Vapor (TPW) from the new NVAP-M Climate Dataset: 25.3 mm', and also on expected trend: 'Expect ~ 7 % TPW / K increase ... current mean ~25 mm'. Li et al, 'Comparison of precipitable water vapor derived from radiosonde,GPS, and Moderate-Resolution Imaging Spectroradiometer measurements' doesn't give a global value but at one land location around 50° N gives 17 mm, also casting 10 mm into doubt. An Elsevier page gives some diverse figures: about 30 mm in a 2020 graph by Li et al, comparing AMSR2 and GOES-16; and from Liang (2013) 'The precipitable water ranged from 0.1 to 78.1 mm with a global average of 21.6 mm'.

The 25 mm value appears most often. Science of Doom may have some useful references including Trenberth & Smith (2005) 'The mean mass of water vapor is estimated as 1.27 × 10^16 kg.... water vapor contribution varies with an annual cycle of 0.29-hPa, a maximum in July of 2.62 hPa, and a minimum in December of 2.33 hPa', consistent with a value > 23 mm. Science of Doom also includes 'The average depth (in this tub) from all around the world would be about 2.5 cm. Near the equator the amount would be 5cm and near the poles it would be 0.5 cm.' which I surmise comes from a 1995 AGU publication that unfortunately is not directly online (Mockler S B, Water vapor in the climate system, special report, AGU, Dec 1995). However, seems to be a useful extract:
 * If all the water vapor in the air at a particular time were to condense and fall as rain, it would amount to a depth of only about 2.5 cm. This is called precipitable water. Because water vapor is not evenly distributed globally, there would be about 5 cm near the equator and less than one tenth as much at the poles.

I think from the context that this is also the basis of the original text in the article. I'm not quite sure how to edit to reflect all this and it would be great if someone with access to more reliable material could review changes including any I make. Calculating a global mean from data sources such as AMSR-2, GOES, MODIS or ISCCP (above) seems fraught with issues of partial coverage and multiple instruments so would be original research. --Cedderstk 08:05, 22 August 2021 (UTC)

Water vapor is also called steam
One of the synonyms for water vapor is the word steam. Maybe it is worth mentioning that in the article? Blacky the Bre (talk) 15:24, 4 July 2023 (UTC)


 * Steam is not an exact synonym. 'Steam' is usually used to refer to water vapor that has been produced by boiling water, implying that it is hot. Wet steam refers to water vapor that also contains small droplets of liquid water. Dezaxa (talk) 17:15, 4 July 2023 (UTC)
 * Oh. That makes sense. Blacky the Bre (talk) 17:51, 4 July 2023 (UTC)