Atmospheric Gas Water Vapour
There are many gases of varying quantities, in the Earth's atmosphere, although nowadays it seems only one is discussed - Carbon Dioxide (CO2).
According to NASA https://nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.html "by volume, in a dry atmosphere, 78.08% Nitrogen, 20.95% Oxygen, 0.934% Argon, 0.042% Carbon Dioxide, which adds up to 100.006%" then add, "other gases 0.268%" which makes 100.273%, clever, but they then say "numbers do not add up to 100% due to roundoff and uncertainty. Water is highly variable, typically makes up about 1%."
Wikipedia say "By volume, dry air contains 78.09% nitrogen, 20.95% oxygen, 0.93% argon, 0.04% carbon dioxide, and small amounts of other gases. Air also contains a variable amount of water vapor, on average around 1% at sea level, and 0.4% over the entire atmosphere." https://en.wikipedia.org/wiki/Atmosphere_of_Earth It is worth reading reference , which states:
"Two recent reliable sources cited here have total atmospheric compositions, including trace molecules, that exceed 100%. They are Allen's Astrophysical Quantities (2000, 100.001241343%) and CRC Handbook of Chemistry and Physics (2016-2017, 100.004667%), which cites Allen's Astrophysical Quantities. Both are used as references in this article. Both exceed 100% because their CO2 values were increased to 345 ppmv, without changing their other constituents to compensate. This is made worse by the April 2019 CO2 value, which is 413.32 ppmv. Although minor, the January 2019 value for CH
4 is 1866.1 ppbv (parts per billion). Two older reliable sources have dry atmospheric compositions, including trace molecules, that total less than 100%: U.S. Standard Atmosphere, 1976 (99.9997147%); and Astrophysical Quantities (1976, 99.9999357%)"
Interestingly neither the UK Met Office nor the World Meteorological Office, don't mention anything about the main atmospheric gases, only "greenhouse" gases, as such they do not include, nitrogen, oxygen, argon (99%), or water vapour.
My argument from the examples from NASA and Wikipedia above is, Earth most certainly does not have a dry atmosphere, so why are the percentages of gases, particularly water vapour, accounted for as a percentage of a dry atmosphere. Surely this is an oxymoron, logic tells me water vapour would be zero in a dry atmosphere, by definitions of "dry" and "water".
I would like to know what happens to the percentages of all the other atmospheric gases in a real atmosphere when water vapour is introduced. Do these other gases decrease in proportion, or does the atmosphere expand by the percentage of water vapour and the percentages of all gases stay the same, some of both, or another explanation?
To find out how much water vapour is in our atmosphere I conducted a series of investigations. Using satellite images, radiosonde soundings, and nullschool information.