Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Atmosphere layer

  1. Dec 16, 2015 #1
    Dear PF Forum,
    Our atmosphere consist of 78% N2, 21% O2, 0.9% Argon, and other...
    Atmosphere Gas.jpg
    What about theses gases? Will they form a layer like this liquid because of their buoyancy difference?
    Or they will be scattered evenly because of the wind.
    I think they will be scattered evenly. But I'm just curious.
  2. jcsd
  3. Dec 16, 2015 #2
    If there is no wind then very gradually the component gases should separate similarly to the liquids shown in the picture.
    However there IS wind and this mixes them up at much faster rate than they could separate, so we don't see any separation usually.
    Some exceptions to consider though.
    1. In deep mines, heavier gases such as CO2 and Radon do become more concentrated unless artificial ventilation is applied.
    2.Hydrogen, being the lightest of gases by a very big margin does tend to rise to the top of the atmosphere despite wind.
    Being of low mass compared to other gases it then is vulnerable to solar wind particles, which can remove it from Earth altogether.
    3. There is at least one situation where a gas in the middle atmosphere does have significantly higher concentration, the Ozone layer, I'm not sure offhand what causes this though.
    Last edited: Dec 16, 2015
  4. Dec 16, 2015 #3

    jim mcnamara

    User Avatar

    Staff: Mentor

  5. Dec 17, 2015 #4


    User Avatar
    Gold Member

  6. Dec 17, 2015 #5
    Thanks for the answer rootone. I might have forgotten that in a deep well, there are poisonous gas. That people who climb down in a deep well might get injured. Yes, so the gas is scattered, but if there's no wind as in a deep well/mine, it will be layered just as the liquid in a glass.
    Actually, I'm studying and doing composting. I just want to know how do we introduce oxygen. Will the oxygen (since it's lighter than CO2) enter the bin from the upper hole and carbon dioxyde expelled from the lower hole. But that's for other thread.
    Thanks for the answer.
  7. Dec 17, 2015 #6
    Good thread, but already closed. For 1 speculation post I think.
    So it's wind and surface tensor. Right, the more I think, it doesn't make sense that the atmosphere is layered like the glass. If it were, than that would be... O3 at the bottom, right. Since it's the heaviest atmosphere gas I think.
    Very hot and good link 256bits. Thanks.
  8. Dec 19, 2015 #7


    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    as a quick response ..... not likely, for a significant reason, can you think what that may be ?

  9. Dec 19, 2015 #8
    Because it seems that the atmosphere is mixed, CO2 (very small amount of it), N2 and O2 (and Ar) they are all mixed and scattered not layered.
    Second, I think the gas pressure inside the composter (because there are some chemical reaction in it, bacteria digesting) is higher than the atmosphere, so gas will be expelled from both lower and upper hole.
    I think only after the reaction diminished and the pressure inside the composter is lower than the atmosphere , then the Oxygen (along with nitrogren, CO2) will enter the composter from the upper hole (depends on the buoyancy of the gas inside the composter).
  10. Dec 20, 2015 #9


    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    That may have an effect, but I was thinking of something more significant .... have another think about processes occurring in the compost pile
  11. Dec 20, 2015 #10
    Thanks Davenn for your responses.
    They say (I don't know, I've never actually researched it. I just read it in the net) that the composting process is the reverse of photosynthesis. That is
    C6H12O6 + 6O2 -> 6CO2 + 6H2O + heat.
    Someone said in PF forum, that the reverse of photosynthesis is true, but the process is not that simple, it involved nitrogen and some other element.
    So the composting expelled CO2 and water,
    But my composter bin, I think, is for anaerobic composting.
    Composter Bin - Small.jpg
    So, it does not expleled CO2 and water. Instead it expelled CH4 and H2S.
    But before I go further, let me give you the atmosphere facts first.
    By volume the atmosphere contains:
    N2 78.08%
    O2 20.94%
    Ar 0.93%
    CO2 0.0397%
    the other Ne, Helium, Methane are too small fraction.
    List of molecular weight compared to H -> 1.008. I divide those number by Hydrogen weight, so it will be an easier conversion.
    Nitrogen: 27.8
    Oxygen: 31.75
    Argon: 39.63
    CO2: 43.66
    Multiply those numbers by volume divided by total volume divided by Hydrogen weight, I have the weight of the earth atmosphere is 28.74 times of the weight of Hydrogen.
    The weight of CH4 compared with H is 15.91
    The weight of Hydrogen Sulfida compared with H is 33.82
    Okay, now back to your question:
    I think I stick to my earlier answer. The gas in the composting will be expelled IF the pressure in the composter bin is higher than the atmospheric pressure, not matter what gas inside. I've already calculated the density of the gas and atmosphere. But on second thought I think that doesn't matter. Only the pressure in the composter bin matters.
    If I were a detective, I would have lost this case. I'm sorry, I'm lost here. What do you think why the oxygen is not likely enters the composter bin from above? Is it gas pressure?


  12. Dec 21, 2015 #11
    On second thought, I think I don't have to divide the weight by hydrogen weight.
  13. Dec 21, 2015 #12
    I know, I know! (raising hand)
    Heat. The composting process is exothermic. A lot of heat is produced; a hot pile can exceed 150F. This is generally desired, to kill weed seeds and pathogens.
    All gases will tend to enter the bottom (or sides, if the pile sits on a surface of low porosity) and exit the top.
  14. Dec 21, 2015 #13
    Yeah, that's what I guess, too. The pile produces heat, and the air pressure in the chamber/composter is higher than the atmosphere.
    But, no matter how. The gas will exit from top and bottom, I think.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook