I have been off sick with the flu for the last five days so I’ve had a lot of time on my hands. Taking into account delirium, boredom, unseasonably warm weather, cabin fever and the fact that I haven’t had a Chemistry class in 15 years, I have some questions about CO[sub]2[/sub].
In light of all the press these days about Global Warming, my questions have to do with anthropogenic carbon dioxide.
When I was in college, we did numerous experiments with CO[sub]2[/sub], the simplest and most graphic of which demonstrated that it is heavier than air.
First question: if it’s heavier than air, where in our atmosphere is all this excess carbon dioxide settling?
Second question: considering the Global Carbon Cycle, if we were to find a non-harmful way to remove some of the carbon dioxide from the oceans, wouldn’t the oceans then act as a natural sink for our excess CO[sub]2[/sub]?
[sub] According to the Department of Energy, human activity (coupled with changing land use/deforestation) is contributing an extra 3.2 billion metric tons of CO[sub]2[/sub] into the atmosphere.[/sub]
It isn’t. It’s true that in still air, CO[sub]2[/sub] will settle into the low-lying areas, but in the outside, winds and atmospheric turbulence keep it pretty well mixed with the rest of the air.
It seems to me that if we could do that, we could just as easily remove it from the atmosphere directly or trap it at the source, without having to move all that heavy water around–moving mass takes energy, and the less mass you have to move, the cheaper it is.
Why? Gases don’t settle into layers by weight. If they did, and it was just air turbulence that kept them mixed, then the nitrogen and oxygen in the air would settle out in layers in a still room, with unfortunate consequences for anyone trying to breathe there.
The natural process for removing CO2 from the air is very effective – plants sequester it as living matter, which then dies. Much of what dies is buried, becomes part of soil and rock. Likewise, a similar process in the ocean combined with carbonate shell formation and the precipitation of calcium and magnesium-calcium carbonates producing layers of carbonate rock (limestone, dolostone). The problem is that these operate over a much longer time frame than does combustion – hence, it is easy to pump more CO2 into the air (and eventually into the water) than is naturally removed.
Water, on the other hand, cycles much more rapidly – load up the atmosphere with H2O, and it precipitates out, as rain, snow, sleet, hail, and gloom of night (well, not the last). Hence, while water vapor is a more effective greenhouse gas than CO2, it’s one that’s much more self-correcting.
IIRC, the effective way to scrub CO2 in any quantity is with some form of lime – calcium oxide. Which would take substantial energy to produce, and in our current energy regime, we’d be putting more CO2 in the atmosphere producing the lime than it would scrub out, by a couple orders of magnitude on a guess.
Sure they do. There’s not much of a density difference between O[sub]2[/sub] and N[sub]2[/sub], but CO[sub]2[/sub] is quite a bit heavier; MW of 28, 32, and 44 respectively.
Under some conditions, pools of carbon dioxide gas can be a hazard:
Gases always expand to fill the whole of the container they are in, with the same pressure throughout. Furthermore, unlike liquids or solids, gas molecules are *not * in contact. Each molecule is flying through space with no interaction with the other molecules (apart from the occasional collision).
A CO[sub]2[/sub] molecule flying through empty space inside a container has no way of “knowing” that there are other molecules in the container that are lighter than it; and therefore has no reason to “settle out” at the bottom.
Even if a CO[sub]2[/sub] molecule were to strike a N[sub]2[/sub] or O[sub]2[/sub] molecule, it would be as likely to be deflected upwards as downwards, since the effects of gravity are negligible on these scales.
Hardly: Sulfur hexafluoride Boat Demo (video)
For light molecules, the temperature of the atmosphere is enough to keep things mixed. As molecules get heavier, not so much. CO[sub]2[/sub] is heavy enough that it tends to stream along the ground, as happened at lake Nyos.
So suppose we were to dump massive amounts of an ammonium chloride buffered solution of calcium hydroxide into the oceans. This would precipitate the carbonate as calcium carbonate thus causing more atmospheric carbon dioxide to dissolve which could then be percipitated out again. Assuming we could produce all that calcium hydroxide and ammonium chloride I don’t see why this wouldn’t work. I’m sure the ocean ecology would be devastated, but it would produce a very good carbon sink. Calcium carbonate is basically rock so that will just sink. Trouble is all the energy required to produce the calcium hydroxide and especially the ammonium hydroxide would probably produce more carbon dioxide than it removed from the atmosphere.
Wasn’t there some plan about dumping ferrous sulfate into the oceans? I think they found that this caused algea to bloom thus taking in carbon dioxide. The problem with this of course is that after a while the alea dies and decomposes back to CO2.
So you release the CO[sub]2[/sub] from any fuel you burn to heat the limestone , plus the CO[sub]2[/sub] from the lime itself.
There aren’t any calcium oxide mines around to let us bypass that step.
CO(sub)2(/sub), typed with square brackets gives CO[sub]2[/sub].
Yep. It’s also the reason that places which deal with large amounts of CO[sub]2[/sub], such as restaurants and carbonated beverage bottlers, must have carbon dioxide sensors installed in low-lying areas, such as basements.