fred2014 Posted January 31, 2016 Posted January 31, 2016 Sorry if this is a stupid question but it's outside my field and just something I was curious about... As we burn fossil fuel we release Co2 "into the atmosphere" So my question is - does this Co2 collect in a band around the planet at a particular altitude or is it dispersed at all levels throughout the atmosphere?
John Cuthber Posted January 31, 2016 Posted January 31, 2016 In general, it's mixed into the atmosphere as a whole.However there's a slightly uneven distribution because, for example, the Northern hemisphere produces more than the Southern one. Locally you get "clouds" of it above major cities and countries with denser populations. It doesn't usually vary much with altitude- at least not at altitudes where you could still breathe. Here's a map http://earthobservatory.nasa.gov/IOTD/view.php?id=82142
studiot Posted January 31, 2016 Posted January 31, 2016 (edited) Sorry if this is a stupid question but it's outside my field and just something I was curious about... As we burn fossil fuel we release Co2 "into the atmosphere" So my question is - does this Co2 collect in a band around the planet at a particular altitude or is it dispersed at all levels throughout the atmosphere? Neither. In the abscence of a body force a gas expands to fill its material container. The atmosphere has no material container, except at the surface of the Earth. So it is contrained to Earth by the body force of gravity. Now gravity acts differentially on 'heavier' (more massive) particles. We can see this effect in the settling of suspended particles in a liquid. The heavier particles settle first at the bottom and we and up with the lightest on top. The average molecuklar weight of atmospheric particles (molecules) is 30 but carbon dioxide the mw is 44 so you can see it is a 'heavier' particle. The the gaseous makeup of the atmosphere is stratified, like the settling sediment in water with the greatest concentration of carbon dioxide at the Earth;s surface and the percentage of lighter gases increasing with altitude. The stratification is not banded it is gradual. That deals with vertical distribution. Horizontal distribution is fairly even since the mixing times for a gasesous atmosphere is measured in days. By contrast the ocean mixing times can be measured in years to centuries. In the atmosphere, just as in the ocean, where you get a continued concentrated input there will be local variations and a balance will be set up between input and dispersal. Edited January 31, 2016 by studiot
John Cuthber Posted January 31, 2016 Posted January 31, 2016 The the gaseous makeup of the atmosphere is stratified, like the settling sediment in water with the greatest concentration of carbon dioxide at the Earth;s surface and the percentage of lighter gases increasing with altitude. The stratification is not banded it is gradual. The stratification is small. Generally too small to consider.
studiot Posted January 31, 2016 Posted January 31, 2016 The stratification is small. Generally too small to consider. Is that so. Then perhaps you can explain away these figures. http://wordpress.mrreid.org/2014/08/01/the-composition-of-earths-atmosphere-with-elevation/
Ophiolite Posted January 31, 2016 Posted January 31, 2016 Is that so. Yes, that is so. From your own reference: Up to around 100?km the composition is fairly “normal”, in that it’s what we surface-dwellers would expect: mostly molecular nitrogen (N2 rather than N) and molecular oxygen (O2) with a small amount (0.93%) of argon and traces of some other gases (carbon dioxide, neon, etc.). Now space is generally agreed to begin at 100km altitude and - according to your own source - the composition is fairly "normal" within that 100km. So, as John says, the stratification is small.
studiot Posted January 31, 2016 Posted January 31, 2016 Yes, that is so. From your own reference: Up to around 100?km the composition is fairly “normal”, in that it’s what we surface-dwellers would expect: mostly molecular nitrogen (N2 rather than N) and molecular oxygen (O2) with a small amount (0.93%) of argon and traces of some other gases (carbon dioxide, neon, etc.). Now space is generally agreed to begin at 100km altitude and - according to your own source - the composition is fairly "normal" within that 100km. So, as John says, the stratification is small. Does it? Then why does it list the composition of the atmosphere at 1000km altitude? By the time we reach an elevation of 1000?km helium makes up 93% of the atmosphere. This is due to the fact that helium is an unreactive and very light atom (with a mass about one-eighth of oxygen) and thus isn’t held tightly by Earth’s gravitational field. (Helium is so light that it can escape Earth’s gravity entirely.) The bulk of the remainder is hydrogen, also prevalent due to its low mass (about one-sixteenth of oxygen’s).
John Cuthber Posted January 31, 2016 Posted January 31, 2016 (edited) Is that so. Then perhaps you can explain away these figures. http://wordpress.mrreid.org/2014/08/01/the-composition-of-earths-atmosphere-with-elevation/ Yes it's so. Why have you asked me to explain the figures there? We were talking about CO2 and there are no data on that page for CO2 Also, did you read my post? Did you understand it? Why do you seem not to realise the importance of this bit? "It doesn't usually vary much with altitude- at least not at altitudes where you could still breathe." It's fairly easy to explain the near constant composition- all the way up to the beginning of "space". The thermal energy of gas molecules is vastly greater than the gravitational potential energy. in essence they are moving too fast to "settle out". You do realise that almost all of the earth's atmosphere is below 100 Km don't you? The vast majority of molecules are in parts of the atmosphere where the composition is nearly constant (apart from big changes in water vapour). Edited January 31, 2016 by John Cuthber
Ophiolite Posted January 31, 2016 Posted January 31, 2016 Does it? Then why does it list the composition of the atmosphere at 1000km altitude? Are you being deliberately obtuse? Stating where the atmosphere ends is an arbitrary decision. The atmosphere fades into the vacuum of interplanetary space, which is not a true vacuum. When we talk about the atmosphere we generally are talking of the stratosphere down. John made that clear in his post, restricting his comments to an even more limited height - no more than 30,000'. Your article is exploring the the greatly extended and extremely attenuated atmosphere out to 1,000km. I suggest if you took any 100 research papers on atmospheric science you would be unlikely to find more than one or two that dealt with the science of the atmosphere at that altitude.
studiot Posted January 31, 2016 Posted January 31, 2016 Ophiolite the atmosphere at that altitude. Two responders here have chosen to limit the atmosphere quite arbitrarily. Fred did not do that in his OP. or is it dispersed at all levels throughout the atmosphere? We have also had a recent thread about the 'limit' of the atmosphere and these arbitrary limits were discussed, but the physics answer was that the atmosphere never actually stops in our models. Yes there are good reasons for these limits but that was not the question. It's fairly easy to explain the near constant composition- all the way up to the beginning of "space". The thermal energy of gas molecules is vastly greater than the gravitational potential energy. in essence they are moving too fast to "settle out". I still challenge that. Consider a shaft in the ground 2 metres square in section, 5 metres deep and open to the atmosphere. However the the atmosphere in the shaft comprises over 20% carbon dioxide. How long will it take for the atmosphere to equalise with the lower % in the normal atmosphere above? In case you are wondering this was the standard video shown in 1990 by HSE when I did my confined space training. Three men died of suffocation in that shaft over the course of more than a day.
Ophiolite Posted January 31, 2016 Posted January 31, 2016 The OPs question is "Where is the CO2?" The CO2 present in the attenuated atmosphere beyond 100km is a tiny percentage of the CO2 present in what any reasonable person would consider to be the atmosphere for any reasonable discussion. Regardless of how CO2 may be distributed in the extended atmosphere it would have no meaningful significance. #I suggest you do the simple calculations involved and satisfy yourself of that fact, or present the numbers that will show I am mistaken.
John Cuthber Posted January 31, 2016 Posted January 31, 2016 "Two responders here have chosen to limit the atmosphere quite arbitrarily." Along with everyone else. If you don't then you end up having to include the whole of the universe and that's plain silly. Practically none of the earth's atmosphere is above 100 KM so it's perfectly sensible to ignore it. And you are now starting to argue against yourself. This question "Consider a shaft in the ground 2 metres square in section, 5 metres deep and open to the atmosphere. However the the atmosphere in the shaft comprises over 20% carbon dioxide. How long will it take for the atmosphere to equalise with the lower % in the normal atmosphere above?" is a question about diffusion. And diffusion is the process that spreads the gas horizontally away from cities etc. But, as you say "horizontal distribution is fairly even since the mixing times for a gasesous atmosphere is measured in days." So, you are saying that horizontal diffusion is fast, but horizontal diffusion is slow. So, having discarded the "how long" question because you answered it (albeit twice, but with different spin). you then need to look at the equilibrium concentration. (because the atmosphere has been here a long time - the eqm with the ocean is a different, slower matter). The concentration at equilibrium will pretty much follow a Boltzmann distribution. Molecules that are higher will have a higher gravitational energy . The relative populations will depend on the energy differences and on the temperature. (This is true whether you "challenge" it or not- the atmosphere doesn't care about your opinion). OK consider a molecule of oxygen It's mass is about 5.356 x 10-26 kg. And, if it gains an extra metre in height the energy change (Mgh) is about 9.8*1* 5.356 x 10-26 kg. 5.26x10-25 J Now the kinetic energy (up and down) of that molecule is roughly the product of the temperature and Boltzmann's constant. (1.380 × 10-23 J/K ) Say it's freezing cold just to define the temperature as about 273K. That gives the molecule a thermal energy of about 3.77 *10-21 J So the kinetic energy in each direction is roughly 7162 times more than the gravitational energy of rising my 1 metre. There are 3 dimensions the molecule can move in 21486 times more kinetic energy than garvitational So the ratio of the populations of those two states is about e^ 1/41486 which is something like 1.000046. (that's an estimate of how much higher the pressure is at ground level,compared to 1 metre further up. Now, if we do the same thing with CO2 molecule we get a KE to thermal energy ratio of 21486 *32/44= 15626 (the thermal energies are the same thanks to the equipartition principle and the CO2 molecules gravitational energy is 44/32 times higher because it's heavier) And the corresponding ratio of populations is 1.000064 So the enrichment is something like 1.000046/1.000064 per metre The expected change in concentration ratio of CO2 and oxygen is 1.000018 per metre Something like 1.8% for a kilometre. And remember, that's an upper bound. Any winds or air currents etc will cause it to mix better than that. So it's no great shock to most of us that the figures show that, up to the edge of space, the CO2 levels are pretty consistent with altitude. Now you may remember that I posted a link to a picture of the worldwide variation with location. Here's a pictureOne interesting thing on that map is the scale. It goes from 391 to 402 ppm. That's about 397=/- 1.4% The horizontal variation is about 1.5% And, according to the page cited by studiot, the variation of practically all the atmosphere with height is less than 1 % So, the following statement he made "The the gaseous makeup of the atmosphere is stratified, like the settling sediment in water with the greatest concentration of carbon dioxide at the Earth;s surface and the percentage of lighter gases increasing with altitude. ... Horizontal distribution is fairly even since the mixing times for a gasesous atmosphere is measured in days." "needs revision" because the stratification is rather smaller than the horizontal variation. 2
Ophiolite Posted January 31, 2016 Posted January 31, 2016 Studiot, with almost 5,000 posts you are going to screw up occasionally. The elegant thing to do is to concede you were caught up in the moment and withdraw gracefully. 1
studiot Posted February 1, 2016 Posted February 1, 2016 Since I have no intention of turning this into an unseemly schoolyard slanging match I am going to make brief comments of the last couple of posts then present my own alternative view, which does not accord. Fred can then choose his own. interpretation. Thank you , John for all that working off of the Sunday roast. I don't doubt you figures except for one thing. You clearly misunderstood my example about the hole in the ground. I said, and I meant, that the Earth's atmosphere ie stratified. And that that statification is due to the varying pull of gravity on molecules of diffeent molecular weight. I should have added there is a second mechanism at work so will detail this in a moment. Stratified not continuously graded. Stratified means 'divided into (horizontal) layers of different composition. I am taking the atmosphere as being that body of gas that has a gravitational attachment to the Earth. So my information is that the layers are as follows. Up to 72 miles the composition is basically a mix of nitrogen molecules and oxygen molecules with 'traces' of other gasses. Since the molecular weight of nitrogen and oxygen is almost the same, and as John says, the molecules are moving pretty fast, there is no further stratification and negligable gradation within this layer. The composition changes above this height as the oxygen molecules and to a lesser extent the nitrogen dissociate. At about 600 miles the composition changes again the principle gas now being helium At about 1500 miles the composition changes again and this is where you will find most of the hydrogen in the atmosphere. Gasses beyond 21,000 miles have an average speed in excess of escape velocity so that is my upper limit of the atmosphere. So my stratifiaction occupies 5 distinct layers for the whole atmosphere. Now note layer 5 in particular. Mostly hydrogen. To bring this back to the Earth's surface and what I said about 'lighter' molecules consider the following thougth experiment. Line up some moderately tall jars of gas with lids. The jars contain carbon dioxide, nitrogen, methane, hydrogen. What will happen when I remove the lids? Why do you think gas detectors in buildings are mounted on the ceiling not the floor? I think the hydrogen leaves the jars immediately and heads skywards. The methane also migrates quickly upwards (hence my question about gas detectors). The nitrogen jar will take perhaps one hour to exhange enough molecules to have the same nitrogen/oxygen ration as the surrounding air The carbon dioxide will remain in the jar and still be in greater concentration than normal on the following day.
Strange Posted February 1, 2016 Posted February 1, 2016 You clearly misunderstood my example about the hole in the ground. https://en.wikipedia.org/wiki/Law_of_holes 2
studiot Posted February 1, 2016 Posted February 1, 2016 (edited) Strange, I have added +1 since I take it in good spirit, not as in any way disrespectful for those three souls who died in that hole (which I think was in Kent by the way) Edited February 1, 2016 by studiot
Strange Posted February 1, 2016 Posted February 1, 2016 Strange, I have added +1 since I take it in good spirit, not as in any way disrespectful for those three souls who died in that hole (which I think was in Kent by the way) Huh! Wha? What three souls died? Which hole? When? What did I miss? I thought we were talking about the composition of the atmosphere?
studiot Posted February 1, 2016 Posted February 1, 2016 Post#10 Consider a shaft in the ground 2 metres square in section, 5 metres deep and open to the atmosphere. However the the atmosphere in the shaft comprises over 20% carbon dioxide. How long will it take for the atmosphere to equalise with the lower % in the normal atmosphere above? In case you are wondering this was the standard video shown in 1990 by HSE when I did my confined space training. Three men died of suffocation in that shaft over the course of more than a day
Strange Posted February 2, 2016 Posted February 2, 2016 (edited) Ah, sorry. I missed that. Even when I went back to look for it.... While interesting, it is, of course, like most of your posts in the thread, utterly irrelevant to the question asked (under any reasonable assumptions about what the OP wanted to know). Edited February 2, 2016 by Strange
John Cuthber Posted February 2, 2016 Posted February 2, 2016 Since I have no intention of turning this into an unseemly schoolyard slanging match I am going to make brief comments of the last couple of posts then present my own alternative view, which does not accord. Fred can then choose his own. interpretation. Thank you , John for all that working off of the Sunday roast. I don't doubt you figures except for one thing. You clearly misunderstood my example about the hole in the ground. I said, and I meant, that the Earth's atmosphere ie stratified. And that that statification is due to the varying pull of gravity on molecules of diffeent molecular weight. I should have added there is a second mechanism at work so will detail this in a moment. Stratified not continuously graded. Stratified means 'divided into (horizontal) layers of different composition. I am taking the atmosphere as being that body of gas that has a gravitational attachment to the Earth. So my information is that the layers are as follows. Up to 72 miles the composition is basically a mix of nitrogen molecules and oxygen molecules with 'traces' of other gasses. Since the molecular weight of nitrogen and oxygen is almost the same, and as John says, the molecules are moving pretty fast, there is no further stratification and negligable gradation within this layer. The composition changes above this height as the oxygen molecules and to a lesser extent the nitrogen dissociate. At about 600 miles the composition changes again the principle gas now being helium At about 1500 miles the composition changes again and this is where you will find most of the hydrogen in the atmosphere. Gasses beyond 21,000 miles have an average speed in excess of escape velocity so that is my upper limit of the atmosphere. So my stratifiaction occupies 5 distinct layers for the whole atmosphere. Now note layer 5 in particular. Mostly hydrogen. To bring this back to the Earth's surface and what I said about 'lighter' molecules consider the following thougth experiment. Line up some moderately tall jars of gas with lids. The jars contain carbon dioxide, nitrogen, methane, hydrogen. What will happen when I remove the lids? Why do you think gas detectors in buildings are mounted on the ceiling not the floor? I think the hydrogen leaves the jars immediately and heads skywards. The methane also migrates quickly upwards (hence my question about gas detectors). The nitrogen jar will take perhaps one hour to exhange enough molecules to have the same nitrogen/oxygen ration as the surrounding air The carbon dioxide will remain in the jar and still be in greater concentration than normal on the following day. "You clearly misunderstood my example about the hole in the ground." No I more or less ignored it because it was irrelevant. But it id dhow that you understand that diffusion happens slowly. And you did, on the other hand, say that it happens quickly. "I said, and I meant, that the Earth's atmosphere ie stratified." Yes, you said it. Yes you meant it No it isn't- at least not this side of space, which means the overwhelming bulk of it is not stratified. Saying it again is no more helpful than strangling the English language with things like " for all that working off of the Sunday roast." "And that that statification is due to the varying pull of gravity on molecules of diffeent molecular weight." As the data you cited show, that stratification is non- existent (except in the vacuum of space)- and I showed you the calculations that explain why; even without wind and convection currents, it would be pretty well mixed. "Why do you think gas detectors in buildings are mounted on the ceiling not the floor?" At least in part, because they don't get covered up if they are up there. But you seem to have missed the point about slow (the time-scale over which the atmosphere has formed) and fast (the time scale over which a room fills with gas). "Now note layer 5 in particular. Mostly hydrogen." Has approximately sod all in it because it's a vacuum. It has nothing to do with the OPs question. Now, please get back to us after you have come to terms with three simple facts. For the overwhelming bulk of the atmosphere- by weight, or number of molecules- the composition is pretty close to the same at at ground level. The atmosphere has had plenty of time to mix. You were wrong. In the mean time, I suggest you take Strange's advice and stop digging.
studiot Posted February 2, 2016 Posted February 2, 2016 In the mean time, I suggest you take Strange's advice and stop digging. OK so You disagree with this national document (in declaring my points irrelevent). http://www.nhbc.co.uk/NHBCPublications/LiteratureLibrary/Technical/filedownload,29440,en.pdf which says that carbon dioxide pools in depressions and methane collects under soffits, ceilings and other spaces confined by horizontal building elements. The document has extensive bibliography at the end to national research and controlling documents. There is also lots of other useful info about the gases. I wish I had this when participating in the design and construction of the Priory Fields commercial and the Salmon Parade residential developments in the 1980s. You are entitled to your opinion and I am entitled to mine without vitriol.
fred2014 Posted February 2, 2016 Author Posted February 2, 2016 OK I seem to have poked a hornets nest here. Sorry - I just thought it was a simple question. The responses have me somewhat confused. I had assumed that this was a cut and dried issue someone could just give a simple answer to - and that coloured map makes no sense to me at all. I'm more confused now than when I asked!
studiot Posted February 2, 2016 Posted February 2, 2016 OK I seem to have poked a hornets nest here. Sorry - I just thought it was a simple question. The responses have me somewhat confused. I had assumed that this was a cut and dried issue someone could just give a simple answer to - and that coloured map makes no sense to me at all. I'm more confused now than when I asked! Sorry Fred, but you just mentioned the atmosphere, which does have layers as I described. JC refers only to the lower atmosphere which has such an overwhelming concentration of oxygen and nitrogen that any variation of other gasses (eg carbon dioxide is about 0.03 %) tends to get lost in the big figures. The other layers form the upper atmosphere and carbon dioxide does not extend this far so its presence largely concentrated in the lower atmosphere band.
Strange Posted February 2, 2016 Posted February 2, 2016 which says that carbon dioxide pools in depressions and methane collects under soffits, ceilings and other spaces confined by horizontal building elements. Yep. Sounds totally irrelevant. JC refers only to the lower atmosphere .. Or what most people would refer to as "the atmosphere". Sorry - I just thought it was a simple question. Unless you are interested in the amount of CO2 at the edge of space, at the bottom of wells or in ceiling spaces, you can just take John's first answer as the definitive one. If I can summarise: There is a small variation in different places because of where CO2 is generated (or absorbed by forests); there is no significant variation with altitude (unless you go to space or down a well).
Sensei Posted February 2, 2016 Posted February 2, 2016 (edited) [...] I think the hydrogen leaves the jars immediately and heads skywards. Speed of sound of Hydrogen gas at room temperature is approximately 1300 m/s. PM me, I will tell you how to make experiment with it. The methane also migrates quickly upwards (hence my question about gas detectors). The nitrogen jar will take perhaps one hour to exhange enough molecules to have the same nitrogen/oxygen ration as the surrounding air The carbon dioxide will remain in the jar and still be in greater concentration than normal on the following day. There is experiment, that probably anybody who has access to dry ice, tried at least once in life. Paper boats, balloons or bubbles, floating in empty aquarium. You can make experiment how long something will float inside of aquarium with dry ice on the bottom and record by camera in timelapse mode. (on YT people are interested in effect, instead of measuring how fast/slow it will disappear) Same idea but with different heavier gas SF6 Edited February 2, 2016 by Sensei 1
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