I If air is a mixture, why don't the gases separate?

[AMan24]

If you try to mix water and sand, the sand will mix around and eventually fall to the bottom. Sand and water can't make a solution, so they separate. However salt and water can make a solution, and they don't separate. If air is a mixture, why don't the gases separate?

1) So, pretty much what I'm asking is, is there a term for a solution of gases?
2) Is it just called a solution?
3) Or am i completely off track and is it something totally unrelated?

4) I was also thinking, why don't they separate because of density?

 

[russ_watters]

The gases in the atmosphere do separate somewhat, but because the atmosphere gets pretty mixed-up by wind, they don't separate that much.

 

[Dale]

The gases in the atmosphere do separate somewhat.

I didn't know that! That is interesting. Do they just separate by density? There is no surface tension so I would imagine that any such separation would be gradual.

 

[anorlunda]

I didn't know that! That is interesting. Do they just separate by density? There is no surface tension so I would imagine that any such separation would be gradual.

I believe free hydrogen in the atmosphere is an example. Most of it rose to the fringes of space and disappeared long ago.

 

[Chestermiller]

At the laboratory scale, the main mechanism is rapid diffusion resulting from the high kinetic energy of the molecules. Even over most of the atmosphere, small scale turbulence combined with diffusion provides most of the story. Only high up in the atmosphere, where the mean free path of the molecules is much larger, does gravitational segregation play much of a role.

Chet

 

[sophiecentaur]

Only high up in the atmosphere, where the mean free path of the molecules is much larger, does gravitational segregation play much of a role.

Why wouldn't gravity have an equal effect all the way up (statistically)? It seems to me that, with or without collisions, the distributions of heavy and light molecules would have the same effect on each other, despite the random motions. Is there something 'different' at work when gases are well intermixed?

 

[Chestermiller]

Why wouldn't gravity have an equal effect all the way up (statistically)? It seems to me that, with or without collisions, the distributions of heavy and light molecules would have the same effect on each other, despite the random motions. Is there something 'different' at work when gases are well intermixed?

Hummm. Good question. I'm not sure. Maybe it has something to do with the gravitational force on each molecule staying about the same, while the frequency of collisions with other molecules decreases as the altitude increases.

 

[lightarrow]

Why wouldn't gravity have an equal effect all the way up (statistically)? It seems to me that, with or without collisions, the distributions of heavy and light molecules would have the same effect on each other, despite the random motions. Is there something 'different' at work when gases are well intermixed?

What do you mean with "the distributions of heavy and light molecules would have the same effect on each other"? I would say diffusion can't happen in absence of collisions.

--
lightarrow

 

[anorlunda]

Why wouldn't gravity have an equal effect all the way up (statistically)? It seems to me that, with or without collisions, the distributions of heavy and light molecules would have the same effect on each other, despite the random motions. Is there something 'different' at work when gases are well intermixed?

Even though we do not normally speak of buoyancy with respect to uncontained gasses, that is what is happening here on a molecular level. Lighter gas molecules are more buoyant than heavy ones. That is why a helium balloon rises. Pop the balloon and the helium gases rise anyhow.

 

[Chestermiller]

Even though we do not normally speak of buoyancy with respect to uncontained gasses, that is what is happening here on a molecular level. Lighter gas molecules are more buoyant than heavy ones. That is why a helium balloon rises. Pop the balloon and the helium gases rise anyhow.

This definitely doesn't sound correct to me. Are you saying that, in a sealed room containing helium in air, the helium will all segregate near the ceiling, and the air will stratify below?

Chet

 

[anorlunda]

This definitely doesn't sound correct to me. Are you saying that, in a sealed room containing helium in air, the helium will all segregate near the ceiling, and the air will stratify below?

Chet

Yes, that's what I'm saying.

Edit: Of course the boundary between the helium and air will not be sharp because of diffusion, but the layer should be there.

 

[russ_watters]

This definitely doesn't sound correct to me. Are you saying that, in a sealed room containing helium in air, the helium will all segregate near the ceiling, and the air will stratify below?

Not completely, but it has to separate a little, doesn't it?

I know due to Dalton's law we sometimes treat gases as completely separate(and therefore each occupying the full volume uniformly), but I don't think that is the reality for this context.

See: http://wordpress.mrreid.org/2014/08/01/the-composition-of-Earth's-atmosphere-with-elevation/

Now, virtually all of the variation is above 100km, which makes that hard to read, so I'd like to find some more detail of what those minor gases are doing down low.

 

[anorlunda]

From https://en.wikipedia.org/wiki/Helium

In the Earth's atmosphere, the concentration of helium by volume is only 5.2 parts per million.[76][77] The concentration is low and fairly constant despite the continuous production of new helium because most helium in the Earth's atmosphere escapes into space by several processes.[78][79][80] In the Earth'sheterosphere, a part of the upper atmosphere, helium and other lighter gases are the most abundant elements.​

The same applies to hydrogen. That is why we only find trace amounts of hydrogen and helium in the atmosphere today. It rose and drifted away into space in primordial times.

 

[nasu]

There are some caves rich in carbon dioxide and this gas collects closer to the bottom of the cave.
But I suppose that if the source of CO2 will stop the bottom layer will disperse after some time.
http://www.showcaves.com/english/explain/Speleology/Dogs.html

 

[Chestermiller]

Not completely, but it has to separate a little, doesn't it?

I know due to Dalton's law we sometimes treat gases as completely separate(and therefore each occupying the full volume uniformly), but I don't think that is the reality for this context.

See: http://wordpress.mrreid.org/2014/08/01/the-composition-of-Earth's-atmosphere-with-elevation/

Now, virtually all of the variation is above 100km, which makes that hard to read, so I'd like to find some more detail of what those minor gases are doing down low.

I'm not saying that there isn't a slight effect in a sealed room. But I am saying that, in a sealed room at atmospheric pressure, the molecular agitation would be adequate to guarantee that the amount of segregation would be virtually undetectable. There certainly wouldn't be a mostly helium layer adjacent to the ceiling.

Chet

 

[russ_watters]

Here's a NASA paper on the subject. Just skimmed, but the abstract mirrors our discussion and there is a graph on page 21:

https://www.google.com/url?sa=t&sou...UiWpNzQ5wHr49NbIA&sig2=yiLQRKqbkanOOF3CZVHG0Q

 

[anorlunda]

Also propane. Boats that allowed propane to leak to the low points in the bilge have exploded years after the leak was stopped. Despite limited air circulation, the propane remains layered in the low points.

 

[russ_watters]

I'm not saying that there isn't a slight effect in a sealed room. But I am saying that, in a sealed room at atmospheric pressure, the molecular agitation would be adequate to guarantee that the amount of segregation would be virtually undetectable. There certainly wouldn't be a mostly helium layer adjacent to the ceiling.

Chet

We're agreed. I did not intend to imply the effect would be significant for a small container. Whether it is significant for the lower atmosphere depends on your definition of "significant". But since that issue was the thrust of the OP's question, I think it is significant enough to mention.

 

[Chestermiller]

We're agreed. I did not intend to imply the effect would be significant for a small container. Whether it is significant for the lower atmosphere depends on your definition of "significant". But since that issue was the thrust of the OP's question, I think it is significant enough to mention.

I didn't see anything in the OP's question about air over vertical atmospheric distances on the order of 10's of km. Maybe it's just my perspective as a ChE to think small, on a scale on the order of meters rather than km. (Although I do have some actual experience as an atmospheric scientist).

Chet

 

[nasu]

Also propane. Boats that allowed propane to leak to the low points in the bilge have exploded years after the leak was stopped. Despite limited air circulation, the propane remains layered in the low points.

I read claims of a similar effect in wine cellars. The CO2 will come from the fermentation, in these cases.

 

[russ_watters]

I didn't see anything in the OP's question about air over vertical atmospheric distances on the order of 10's of km. Maybe it's just my perspective as a ChE to think small, on a scale on the order of meters rather than km. (Although I do have some actual experience as an atmospheric scientist).

Since he asked "why don't they separate because of density", I wanted to start off by congratulating him for his correct logic and telling him he's right that they do/should, before hitting him with the big "but".

 

[Chestermiller]

Also propane. Boats that allowed propane to leak to the low points in the bilge have exploded years after the leak was stopped. Despite limited air circulation, the propane remains layered in the low points.

So, in a room filled with stagnant air, the majority of the oxygen molecules will eventually be situated in the bottom 20% of the room, and the majority of the nitrogen molecules will be situated in the upper 80 % of the room (even though air is nearly an ideal gas, with the individual molecules traveling very rapidly in all directions)? How does that reconcile with your helium balloon explanation?

Chet

 

[nasu]

It does not follow. The difference in molecular weight between oxygen and nitrogen is much smaller than the difference between nitrogen and propane, CO2 or helium.
So if the diffusion is enough to equalize O2 and N2 in normal conditions it does not mean is enough in every case.
It would be interesting to have some quantitative estimate of the effect.

 

[DrStupid]

the majority of the nitrogen molecules will be situated in the upper 80 % of the room

That sounds plausible.

 

[Chestermiller]

That sounds plausible.

I sure don't want to try to breathe the air in the upper part of that room.

 

[Chestermiller]

It does not follow. The difference in molecular weight between oxygen and nitrogen is much smaller than the difference between nitrogen and propane, CO2 or helium.
So if the diffusion is enough to equalize O2 and N2 in normal conditions it does not mean is enough in every case.
It would be interesting to have some quantitative estimate of the effect.

In your professional judgement, do you really think there would be a significant effect in these other cases?

Chet

 

[russ_watters]

It would be interesting to have some quantitative estimate of the effect.

Have a look at the link I posted. The graph shows the concentrations of [molecular] oxygen and nitrogen basically constant up to 100km, but gases with much different molecular weights like H and O (monoatomic?) vary noticeably...though those don't exist at the surface.

All that said, I'm no longer certain of the mechanism of the variation. I've only skimmed the theory, but what I saw implies that the variation above 100 km can be entirely explained by Dalton's law and the different molecular weights, not by buoyancy:

Each constituent has a density vs altitude curve who's slope depends on molecular weight: heavy gases weigh themselves down and light ones spread themselves out.

 

[Chestermiller]

Have a look at the link I posted. The graph shows the concentrations of [molecular] oxygen and nitrogen basically constant up to 100km, but gases with much different molecular weights like H and O (monoatomic?) vary noticeably...though those don't exist at the surface.

All that said, I'm no longer certain of the mechanism of the variation. I've only skimmed the theory, but what I saw implies that the variation above 100 km can be entirely explained by Dalton's law and the different molecular weights, not by buoyancy:

Each constituent has a density vs altitude curve who's slope depends on molecular weight: heavy gases weigh themselves down and light ones spread themselves out.

Gases like atomic H and atomic O are in very low abundance because they are created and destroyed by very rapid photochemical reactions. So they can't be regarded on the same basis as inert tracer gases.

 

[nasu]

In your professional judgement, do you really think there would be a significant effect in these other cases?

Chet

My professional judgement tells me to prefer some quantitative parameters rather than just intuition.
I have no direct experience with gas separation.
I just said that the non-separation of N2 - O2 does not necessarily implies non-separation in all cases.

 

[russ_watters]

Gases like atomic H and atomic O are in very low abundance because they are created and destroyed by very rapid photochemical reactions. So they can't be regarded on the same basis as inert tracer gases.

Sure, below 100km it would be safe to say that O2 and N2 dominate and several others vary greatly or are limited due to chemical/thermodynamic processes (water, Ozone too).

Above 100km, it turns out that monoatomic oxygen dominates for a few hundred km, then monoatomic helium. This may be beyond the scope of the OP, but it fascinates me!

 

[Chestermiller]

My professional judgement tells me to prefer some quantitative parameters rather than just intuition.
I have no direct experience with gas separation.
I just said that the non-separation of N2 - O2 does not necessarily implies non-separation in all cases.

Wouldn't you think that the magnitude of the gravitational contribution would be roughly proportional to the difference in molecular weights. So if the segregation of N2 and O2 is zilch, the segregation between air (mw 29) and CO2 (mw 44) at equilibrium would be about 15/4 = ~ 4 times zilch.

 

[sophiecentaur]

What do you mean with "the distributions of heavy and light molecules would have the same effect on each other"? I would say diffusion can't happen in absence of collisions.

--
lightarrow

My wording was really poor, wasn't it?
I was thinking of partial pressures and that the gradients would be expected to be different. Yes, the diffusion will be slowed by collisions (as in a porous medium) but I am sure that the final gradients should turn out to be different for different gases, and the same that you would get if each gas were in isolation around a less massive planet (?).

 

[nasu]

Wouldn't you think that the magnitude of the gravitational contribution would be roughly proportional to the difference in molecular weights. So if the segregation of N2 and O2 is zilch, the segregation between air (mw 29) and CO2 (mw 44) at equilibrium would be about 15/4 = ~ 4 times zilch.

Are you sure it is a linear effect?
Do you have some quantitative basis for this? That will be interesting.

 

[anorlunda]

Let me propose a laboratory experiment that I bet Chet would agree on after some thought.

Take a vertical cylinder container of height L and cross-sectional area A. Let R=L/A.

We will fill it with 1/3 He (1/3 by volume), 1/3 air, and 1/3 CO2.

Now, if there are stratified layers, then mixing will occur at the boundaries between layers because of thermal agitation, or diffusion, or turbulence. But mixing efficiency decreases with A.

So for small values of R, agitation dominates and there will be no measurable layering (zilch layering). But as R increases, mixing efficiency becomes arbitrarily small. Something else must begin to dominate. What candidates are there other than buoyancy? For high values of R, buoyancy dominates and there will be measurable stratified layers in the steady state.

In the lab, rather than directly modifying R, we could start with a pipe, L=10 m, A=$1cm^2$. Then place 2 gate valves to partition the cylinder into 3 equal volume regions. The valves would initially be fully open. The experiment would then be to very gradually close the valves over a period of weeks or months while measuring the proportions of He, air, and CO2 in the regions.

 

[Chestermiller]

Here is a simple calculation that quantifies the effect. I have air (MW =29) and He (MW =4) in a room at 1 atm and room temperature. Such a mixture can be treated as an ideal gas mixture. In an ideal gas mixture, the different gases behave as separate entities. Let:

p_ao= partial pressure of air at the floor
p_h0= partial pressure of He at the floor
L= height of room (nominally 3 m)
z = distance measured upward from the floor
T = absolute temperature
R = ideal gas constant
M_a=molecular weight of air
M_h=molecular weight of helium

For each gas in the ideal gas mixture, the barotropic equation tells us that:

$$\frac{dp}{dz}=-\frac{Mg}{RT}p$$
So as a function of height z in the room, the partial pressures of air and of helium are given, respectively, by:
$$p_a=p_{ao}\exp{\left(-\frac{M_agz}{RT}\right)}$$
$$p_h=p_{ho}\exp{\left(-\frac{M_hgz}{RT}\right)}$$
So the ratio of the partial pressures (and mole fractions) at the ceiling are related to the ratio of the partial pressures (and mole fractions) at the floor by
$$\frac{p_h}{p_a}=\frac{p_{ho}}{p_{ao}}\exp{\left(\frac{(M_a-M_h)gL}{RT}\right)}$$
The term in parenthesis in this equation is equal to ~ 0.0003.

Therefore, the ratio of the mole fractions at the ceiling is equal to the ratio of the mole fractions at the floor times about 1.0003 (i.e., a variation of 0.03%). That's the big stratified separation that occurs.

For a small typical value of the expression in parenthesis like 0.0003, the relationship becomes:

$$\frac{p_h}{p_a}=\frac{p_{ho}}{p_{ao}}\left(1+\frac{(M_a-M_h)gL}{RT}\right)$$

So, to answer nasu's equation in post #33, yes I do have evidence that the change is essentially linear in the molecular weight difference.

Chet

 

[anorlunda]

Here is a simple calculation that quantifies the effect.

My knees quiver to argue with Chestermiller, but here goes.

That partial pressure calculation assumes that the gasses are well mixed. It can't be used to establish the mixing ratios. The NASA paper linked by Russ uses those types of equations for the Homosphere where turbulence guarantees well mixed gases. http://ruc.noaa.gov/AMB_Publications_bj/2009%20Schlatter_Atmospheric%20Composition%20and%20Vertical%20Structure_eae319MS-1.pdf The figure below from the same paper shows the mixing ratios of different gasses. They are highly nonlinear, and not even monotonic. It is unclear from the paper exactly how they define mixing ratio. They discuss it using units ppmv (parts per million volume?) Nevertheless, note that the mixing ratio for O2 is $10^4$ to $10^{10}$ times bigger than the ratio for H. I take that to mean that H is much more reluctant to mix than O2.

The caption says that the ratio for nitrogen is not shown because it is always well mixed.

 

[Chestermiller]

My knees quiver to argue with Chestermiller, but here goes.

That partial pressure calculation assumes that the gasses are well mixed. It can't be used to establish the mixing ratios. The NASA paper linked by Russ uses those types of equations for the Homosphere where turbulence guarantees well mixed gases. http://ruc.noaa.gov/AMB_Publications_bj/2009%20Schlatter_Atmospheric%20Composition%20and%20Vertical%20Structure_eae319MS-1.pdf The figure below from the same paper shows the mixing ratios of different gasses. They are highly nonlinear, and not even monotonic. It is unclear from the paper exactly how they define mixing ratio. They discuss it using units ppmv (parts per million volume?) Nevertheless, note that the mixing ratio for O2 is $10^4$ to $10^{10}$ times bigger than the ratio for H. I take that to mean that H is much more reluctant to mix than O2.

The caption says that the ratio for nitrogen is not shown because it is always well mixed.

In atmospheric science parlance, mixing ratio is the same thing as what we call mole fraction.

Except for oxygen, CO2, and Argon, all the other gases in this figure are strongly affected by the photochemistry. CH4 decreases with altitude because of its reaction with OH radicals, and N2O decreases with altitude because of photolysis and reaction with O¹D. Of course ozone, O atoms, and H atoms are all very highly active photochemically. And water up to the tropopause is controlled by condensation processes at the very low temperatures in the upper troposphere. So the only gases in this figure that have relevance to our discussion are O2, CO2, and Ar. And these gases are seen to have constant mixing ratios all the way up to 80 km. This is a little higher than the 3 meter room I was talking about.

I guess if you were going to use a figure from Guy Brasseur's paper, you should have at least read the paper. I was a very active worker in the atmospheric transport and chemistry area for a number of years when I worked for DuPont. (Incidentally, I knew Guy Brasseur and his frequent co-work Susan Solomon personally during that period). Here are a few of my papers that you may be interested in reading:

Miller, C., Meakin, P., Franks, R.G.E., and Jesson, J.P., The Fluorocarbon-Ozone Theory – V. One Dimensional Modeling of the Atmosphere: The Base Case, Atmospheric Environment, 12, 2481-2500 (1978)

Miller, C., Filkin, D.L., and Jesson, J.P., The Fluorocarbon-Ozone Theory – VI. Atmospheric Modeling: Calculation of the Diurnal Steady State, Atmospheric Environment, 13, 381-394 (1979)

Glasgow, L.C., Jesson, J.P., Filkin, D.L., and Miller, C., The Stratospheric Abundance of Hypochlorous Acid (HOCl), Planet. Space Sci., 27, 1047-1054 (1979)

Miller, C., Steed, J.M., Filkin, D.L., and Jesson, J.P., Two-Dimensional Model Calculations of Stratospheric HCl and ClO, Nature, 288, 5790, 461-464 (1980)

Bass, A.M., Glasgow, L.C., Miller, C., Jesson, J.P., and Filkin, D.L., Temperature Dependent Absorption Cross Sections for Formaldehyde: The Effect of Formaldehyde on Stratospheric Chlorine Chemistry, Planet. Space Sci., 28, 675-679 (1980)

Miller, C., Steed, J.M., Filkin, D.L., and Jesson. J.P., The Fluorocarbon Ozone Theory – VII. One-Dimensional Modeling – An assessment of Anthropogenic Perturbations, Atmospheric Environment, 15, 5, 729-742 (1981)

Miller, C., Filkin, D.L., Owens, A.J., Steed, J.M., and Jesson, J.P., A Two-Dimensional Model of Stratospheric Chemistry and Transport, J. Geophys. Res., 86, C12, 12039-12065 (1981)

Steed, J.M., Owens, A.J., Miller, C., Filkin, D.L., and Jesson, J.P., Two-Dimensional Modelling of Potential Ozone Perturbation by Chlorofluorocarbons, Nature, 295, 5847, 308-311 (1982)

Owens, A.J., Steed, J.M., Miller, C., Filkin, D.L., and Jesson, J.P., The Atmospheric Lifetimes of CFC 11 and CFC 12, Geophys. Res. Lttrs., 9, 6, 700-703 (1982)

Owens, A.J., Steed, J.M., Miller, C., Filkin, D.L., and Jesson, J.P., The Potential Effects of Increased Methane on Atmospheric Ozone, Geophys. Res. Lttrs., 9, 9, 1105-1108 (1982)

Owens, A.J., Hales, C.H., Filkin, D.L., Miller, C., Steed, J.M., and Jesson, J.P., A Coupled One-Dimensional Radiative-Convective, Chemistry-Transport Model of the Atmosphere, 1. Model Structure and Steady State Perturbation Calculations, J. Geophys. Res., 90, D1, 2283-2311, (1985)

Now, I provided an analysis of the problem we have been discussing concerning air and helium in a room in post #36. You claimed that there would be a significantly larger concentration of helium near the ceiling than near the floor, and I showed that there would only be a 0.03% difference. If you have found any flaws in my analysis, please identify them.

Chet

 

[anorlunda]

I stand corrected. Should have known better.

 

[nasu]

So, to answer nasu's equation in post #33, yes I do have evidence that the change is essentially linear in the molecular weight difference.

Chet

I hope you understand that I was rely curious about some quantitative estimate and not challenging you without reason.

 

[Chestermiller]

I hope you understand that I was rely curious about some quantitative estimate and not challenging you without reason.

You rascal. You baited me into it. I figured it out while I was out walking the dogs.

Chet

 

[Mike Bergen]

Look up Dalton"s Law and it will explain how these separate gasses will spread out equally in a container. In this case the atmosphere is pretty big and with half the air we have between sea level and 40.000 ft. The atmosphere never really stops but after 100 miles up the molecules are pretty few and far between

 

[rcgldr]

There have been instances where large amounts of carbon dioxide was released, and initially it stayed close and/or descended to the ground due to being about 1.5 times as dense as normal atmosphere.

 

[PWiz]

There was a really nice answer on Stackexchange as to why the separation of gases in air is not as prominent as a mixture of liquids. I can't say it better in my own words, so here it is:

If a system such as a mixture of gases is kept under constant temperature in a constant volume, the equilibrium state corresponds to the minimum of Helmholtz free energy:
$$A=U - TS$$
As you see, for to reach the minimum either the energy should decrease or the entropy should increase (or both in reality).

Minimizing energy. Most of the energy of common gases at normal conditions comes from their kinetic energy defined by the temperature. Energy due to intermolecular potential is negligible. So the only possibility to lower the energy is to lower the gravitational energy. In essence it would require the mixture to perfectly separate --- heavy gases at the bottom, light gases up.

Maximizing entropy Maximum entropy for the system in hand (under specified conditions) would imply perfect mixture, the state of most disorder. That's actually what drives the diffusion.

So as you see, the equilibrium state is a compromise between low energy and high entropy. For gases the entropy wins, because there isn't much energy difference between a mixture and a separated state (apart from gravity, which is still small).

As for your example with oil and water the situation is opposite. Unlike gases considerable amount of energy in liquids comes from intermolecular forces. Thus there is a huge differences in energy of interaction water-water or water-oil, so it is more preferable do separate to considerably minimize the energy.

(Here's the link if you want to view other answers to that question too: http://physics.stackexchange.com/questions/34733/why-does-air-remain-a-mixture )

 

[Mike Bergen]

I wonder if the propane example is more pronounced because it is more a Vapor than Gas and certainly much heavier than air. Water vapor is interesting because it is lighter than air.

Also the distribution of the mixed gases seems subject to the gravitational effect at that altitude So does it seem that percentage of gas at each altitude is subject to how much of the whole is left at those higher altitudes

 

[Chestermiller]

I wonder if the propane example is more pronounced because it is more a Vapor than Gas and certainly much heavier than air. Water vapor is interesting because it is lighter than air.

You are aware that a vapor is just a gas above its dew point, right?

Also the distribution of the mixed gases seems subject to the gravitational effect at that altitude So does it seem that percentage of gas at each altitude is subject to how much of the whole is left at those higher altitudes

In case you didn't notice it, this effect is addressed quantitatively in post #35.

 

[Mike Bergen]

Chester Miller, My HVAC Trade understanding of Vapor/ Gas is that vapor- liquid is easier to accomplish with less heroic methods than Liquefying gas like O2 Or is it how well they follow the Ideal Gas Laws.
I am a Tradesman and not a Physicist, But I am finding a lot of the discussion interesting

Yes I saw that Fig 2 Mixing Ratio Data and found the N2 omission because it was "well mixed and the O2 and CO2 graphs interesting along with the water vapor H2O

Thanks for the clarification Mike

 

[klimatos]

If the global atmosphere were in a condition of equilibrium (which it most definitely is not), then Dalton's Law would explain the distribution of the individual molecules of the various non-reacting gases quite well. As it is, Dalton's Law does not do a bad job. It produces a very good first approximation. The real free atmospheric distribution of gas molecules is also influenced by fluid flow (winds and currents) which change the local distribution somewhat, and by precipitation--which affects the concentration of water vapor. I think that you will find that Dalton's distribution is approached more closely in the polar areas (where both strong convective storms and precipitation are less common) than in the tropics--where both strong convective storms and water vapor are much more common.

 

[Mike Bergen]

Seems Dalton works on small samples that are not unduly affected by Gravity. That Mixing Ratio Fig 2 , I guess shows the effect of gravity on certain gases like NOX's or H

I believe I read where the height of Atmosphere is lower at Poles along with water vapor so you are right the winds and a lot of other factors are really making this an interesting topic

Thanks for thoughts, Mike

 

[Chestermiller]

Seems Dalton works on small samples that are not unduly affected by Gravity. That Mixing Ratio Fig 2 , I guess shows the effect of gravity on certain gases like NOX's or H

I believe I read where the height of Atmosphere is lower at Poles along with water vapor so you are right the winds and a lot of other factors are really making this an interesting topic

Thanks for thoughts, Mike

Mike,

Please use discretion when you submit posts to Physics Forums. These Forums are not for speculation or guessing. If you're not sure, please do not guess. Your recent posts are bordering on misinformation. For example, Fig. 2 does not show the effect of gravity on certain gases like NOX or H. I know this because I worked in this area and am familiar with how these results were obtained.

Saying that the height of the Atmosphere is lower at the poles is also incorrect. The height of the troposphere, which is the lower part of the atmosphere, is lower at the poles, because the temperature inversion occurs at lower altitudes near the poles than near the equator.

I'm not going to issue warning points this time, by my warning finger is getting itchy.

Chet