A couple of days ago WUWT carried a story, talking about intense cold in Antarctica, carbon dioxide, and the icecap of Mars. This one passage stirred up a significant debate:
According to Weather Underground, Vostok, Antarctica is forecast to reach -113F on Friday. That is four degrees below the freezing point of CO2 and would cause dry (CO2) ice to freeze directly out of the air.
It seemed (at the time) a reasonable statement. The freezing point of CO2 is -109.3 degrees Fahrenheit (-78.5 degrees C). There’s been mentions of this supposed phenomenon of CO2 freezing out of the air before on other blogs and websites. One of the best examples was even an entry in the website “ask a scientist” where the question of CO2 freezing out of the air was posed, and the answer from an Argonne National Laboratory scientist seemed to indicate that CO2 could indeed precipitate as a solid from the air if the temperature was low enough at Earth’s south polar ice cap, specifically at Vostok Station, which holds the record for the lowest surface temperature recorded on Earth at −89.2°C (−128.6°F)
Certainly, at least some of the carbon dioxide in the atmosphere at the poles does freeze out during the winter. However, there is not enough frozen out to accumulate to any extent at the present.
David R. Cook
Atmospheric Research Section
Environmental Research Division
Argonne National Laboratory
So, it seemed possible. But as WUWT commenters soon pointed out, temperature is only part of the equation needed to deposit CO2 as a solid from the free atmosphere at that temperature.
Soon we were discussing gas laws, phase diagrams, and partial pressures. The debate mainly centered on whether or not this phase diagram for carbon dioxide applied to 1 atmosphere of pressure of pure CO2 versus simply 1 atmosphere of pressure independent of the purity of the gas.
The author of the post, Steven Goddard wrote in comments:
The phase diagram shows unambiguously that the equilibrium state of CO2 at one atmosphere at 113F is solid. The freezing point of CO2 is -109F at 1 atmosphere.
The PDF referenced doesn’t translate well to the blog size format, but this less detailed phase diagram for CO2 does fit and was mentioned in comments also:
Since many of us know from experience that with ice, be it water ice or CO2 (dry) ice, that a phase change can occur directly from solid to gas (sublimation). It seemed reasonable to conclude that the reverse could be possible, going from a gas to a solid as long as the temperature was below the “triple point” of CO2 as well as the freezing point at 1ATM.
The freezing point/sublimation point of CO2 at 1ATM is at -78.5C (-109.3F). In the situation described in the forecast for Vostok station, the temperature was forecast to reach below the freezing point for CO2 at -80.5 C (-113F ). It seemed reasonable then to concludes that CO2 would freeze right out of the air, much like frost does from water vapor. Plus we had a statement from a scientist at a National Laboratory saying it was possible also. What’s not to like?
One small detail: partial pressure.
The concentration of CO2 in the free atmosphere is very small. Thus the partial pressure of CO2 in the atmosphere is about 0.0004 atmospheres. But wait there’s more. Vostok station is at a high elevation, 3288 meters above sea level (10,787 feet) and the atmosphere is thinner. Thus the partial pressure of CO2 is even lower.
Commenter George E. Smith summed it up pretty well with this paragraph:
At -78.5 deg C (-109F), that equilibrium occurs at a partial pressure of CO2 of 760 mm Hg, one atmosphere. Below that pressure, there isn’t enough abundance of CO2 molecules in the vapor phase for collisions with the solid surface to occur at a fast enough rate to make up for the ones that escaped; so the solid CO2; dry ice, will continue to sublimate.
Basically, there are so few CO2 molecules in the free atmosphere, sublimation rules over deposition as a solid. Yes some CO2 may deposit on a surface at at -80.5 C (-113F ), but it would quickly sublimate back into the free atmosphere, and thus accumulation would not occur.
Meanwhile WUWT reader Ric Werme had written to Dr. David Cook of Argonne National Lab to ask about his original opinion he wrote for “ask a scientist” web site. Ric reports he responded with this:
Ric,
You are correct. In my attempts at being simplistic I made a mistake in my answer to “Freezing CO2″ on the Ask-A-Scientist page. -57 C is the boiling point of CO2. The freezing point of CO2 at atmospheric pressure is -78.5 C (-109.3 F). If the temperature reaches -113 F at Vostok, Antarctica, some carbon dioxide might freeze out of the air, assuming that the carbon dioxide vapor pressure drops to its saturation vapor pressure.
The vapor pressure must reach the saturation vapor pressure for dew or frost to form. This happens at the dew point or frost point temperature, which is dependent on atmospheric pressure and the absolute amount of vapor in the air. As atmospheric temperature increases, the dew/frost point temperature increases. As atmospheric pressure increases, the vapor pressure increases. At very low temperatures, the dew/frost point temperature is very low.
When the temperature of the surface (whether grass or a car window) is below freezing, frost will usually form instead of dew, although water can be super-cooled and not produce dew, fog, or clouds in some cases. Surfaces on the Earth cool off sooner than the air, so dew/frost will normally form on them before fog (water or ice) forms in the air.
The temperature being at “freezing” or below does not imply that frost will form on surfaces or in the air. The vapor pressure must be high enough (saturation vapor pressure) and the temperature low enough (the frost point temperature) for frost to form.
So it seems, Dr. Cook (and our own Steve Goddard) made the basic and simple error of not taking vapor pressure into account. Given our human experience with the everyday freezing of water, we don’t often think about it. I didn’t catch it either initially, nor did some WUWT commenters.
It does demonstrate though, how little CO2 there is in our atmosphere, we can’t even precipitate it to solid under any natural condition of earth.
But, even with the debate apparently settled, the CO2 freezing question was still all in the realm of opinions and phase diagrams. Some people really wanted to see some empirical proof. Some thoughts on experiments were tossed about.
Enter WUWT reader Dr. Thomas Thatcher of the University of Rochester who had not only an idea for an experiment, but the means with which to carry it out. He had a lab freezer which would “maintains -80˚C (-112˚F) in my lab, and it can be set as low as -86˚C (-122˚F).”.
He proposed that he could use that freezer to do a test with dry ice:
The argument, as far as I can tell, is that at the atmospheric partial pressure of CO2, dry ice at -113F will sublimate faster than it forms (which may be different than how a pure CO2 atmosphere would behave). I am in a position to test this, as described above.
…
Based on the arguments presented here, the two postulated outcomes are,
1) significant loss of mass, as the sublimation rate exceeds the deposition rate
2) no change, or negligible gain in mass.
(I suspect that any gain in mass will evaporate on the short walk from the freezer to the balance.)
It’s admittedly an imperfect experiment. But I expect the outcome will be rather obvious; the dry ice will be gone in the morning. We’ll see.
He conducted his experiment overnight between Thursday and Friday, and writes:
The freezer is a VWR brand ultralow temperature upright freezer, similar to models shown here.
http://www.vwrsp.com/catalog/product/index.cgi?catalog_number=14230-120&inE=1&highlight=14230-120
It is set to -86C, the temperature typically rises 1-3C when opened, and recovers in about 30 minutes. (Factory temperature calibration was NIST-traceable but it has not been recalibrated since it was installed here.) The samples were loaded at 4:30 pm and removed at 9:30 am, so the freezer will have been largely undisturbed during that time.
The interior is mostly filled with stainless steel racks that hold cardboard boxes for storing biological samples. I placed the test samples in two boxes on the bottom shelf at the rear of the freezer, the coldest zone and closest to the temperature probe.
One sample was placed in an open box with extra holes cut to allow air circulation. The other sample was placed in small zip top plastic bag inside a cardboard box. The samples were weighed by difference before being placed in the freezer and after removal in the morning. Additional weighings were taken to estimate the amount of sublimation during the weighing procedure and the amount of water that might condense on the boxes, but these amounts proved insignificant next to the overall results.
The samples were placed in the freezer at 4:30pm (reading -82C) and removed at 10:00am (reading -83C).
Open container, start weight 36.5g dry ice, end weight 0g, amount sublimated 100%.
Zip-top bag, start weight 27.6g dry ice, end weight 25.3g, amount sublimated 8.3%
Proving, I think, that CO2 will freeze and remain frozen at below -78.5C if the partial pressure of CO2 is near 1 ATM, but the CO2 will rapidly sublimate is the partial pressure of CO2 is near atmospheric normal.
And he concludes:
Bottom line, 40g of dry ice placed in an open container at -82C completely sublimated overnight, while 27g of dry ice placed in a zip top bag retained 90% of its mass. This proves two things, first, that the temperature of the freezer did not exceed -78.5C for any appreciable period of time, and second that yes indeed, the partial pressure of CO2 is the key to the problem.
Best of all, he sent photos of the experiment he conducted:
Thanks to everyone who participated in the debate, including Ric Werme for his correspondence help and especially Tom Thatcher for conducting the experiment and taking photos.
We all learned something, we had a little fun, some online yelling occurred, and some egos were bruised. Overall though it was worthwhile that this myth of “CO2 snow at Vostok station” was finally put to rest.
Brilliant !!
You just solved the phantom SWPC/NOAA sunpot issue.
The spots yesterday that nobody imaged or drew but were counted (06-12-2009) sublimated before they could exist.
The spot of 06-10-2009 likewise sublimated after it was draws so that it could not be imaged.
Problem solved.
Throw them out.
open and shut in 72 hours.
wow.
the power of the internet.
Well done. Once again, WUWT lives up to its well-deserved title of Best Science Blog.
Very interesting discussion and explanation. It took me a long time to get a good handle on partial pressure in my nuclear power training, but, now that I’m retired, that nuclear “learning” is still good for something other than giving me a gut feeling that there is something — Q = mc∆T — entirely wrong with AGW theory.
May I add this? When “freezing point” is mentioned (or indeed “condensation point”, boiling point” and so on) you have to ask “under what conditions?”. For CO2, the quoted freezing point refers to atmospheric pressure and – the crucial point – pure CO2. It so happens that you can also use information extracted from the phase diagram to calculate the frost point for CO2 at atmospheric pressure even when CO2 is not pure, but is dissolved in air (in answer to someone’s enquiry in the earlier thread, air is, technically, a solution of O2, N2 ….). Or, to be precise, when CO2 is dissolved in dry air. In wet air, there is the potential for the complication of CO2 and H2O frosting together, as a “hydrate” or “clathrate” – which was one of the most interesting points raised in the earlier thread. You can’t check that possibility in any simple way from the phase diagram for CO2 alone – you’d need some measurements done on that very problem, preferably summarised into a suitable phase diagram.
It’s worth realising that saying “It so happens that you can also use information..” rather disguises the fact that experimental measurement has revealed that “It so happens that …” – strictly, you can’t tell just by hand-waving or assertion, someone had to make the measurements. All this is elementary stuff for, say, chemical engineers or many physical chemists. But many other scientists may never need to understand the issue in a whole career.
One last point – understanding of this “elementary stuff” has been backed by a century’s worth of theory and experiment. That knowledge is therefore infinitely more secure than knowledge about “climate science”, whose proponents are necessarily limited to observations and modelling – you can’t do controlled experiments on the climate. For that reason alone – and there are plenty of others – I find find the global warmmongers’ lack of a sense of proportion, and lack of due humility about their claims, an offence to the spirit of science.
Wonderful!
That is how science should be done.
An ounce of experimental fact outweighs a ton of arm waving.
But it IS enough to worry brass monkeys.
Always good to learn. Thanks to everyone involved.
Bye,
TMTisFree
Well done, and well said.
Anybody else have the pictures *not* show up (unless specifically clicking on each one)?
.
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Well done everyone here who participated in the debate-surely this was science in action, whereby a hypotheses was tested and found wanting.
No mention of Phil, who I think made some very valuable points -a little less snark would go a long way Phil, your comments are always interesting and to be respected, but so are those of others. A triumph for the scientific process. The hockey stick next to be demolished on line? (again)
Tonyb
REPLY: Phil. did indeed make some valuable contributions, but behaved very badly. Note that I also didn’t mention “crosspatch” in the article, although he was actually the very first to identify the issue. Since this article may be cited as a reference in the future when the question arises, I felt it appropriate to only mention contributions to solving the issue from people that use their real name. Science is not advanced anonymously, peer review journals do not accept anonymously submitted letters/papers with snark attached, why should we?
That, and I don’t believe in rewarding bad behavior. There was too much labeling of people by some commenters, and it was entirely unprofessional and unnecessary. We really don’t do anyone any favors when we revert to this level while trying to educate and enlighten online. – Anthony
Ric, George, Phil, Steve, David, Thomas, Anthony…..
I am thrilled to bits for this education. It swept off over 50 years of dust, added a lot of new material and had me brushing up on Boyle, Gay-Lussac, Avogadro, Henry, Boltzmann, phase rule, ….. and the honour of feeling part of a society of giant intellects that let others like me make my little offerings at will. And this is just one of the kaleidoscope of topics from solar physics to ocean chemistry and currents, biology, and expansion of my own geological and engineering field. This is got to be the future of education when this medium can inspire an old dog like me.
If C02 is heavier than air, what affect will this have on its “freezing out” of the atmosphere as snow?
The sign on the wall of the Metrology/Calibration lab I worked in:
ONE TEST IS WORTH A THOUSAND EXPERT OPINIONS
Thanks, Dr. Thatcher.
I really hate phase diagrams. Geologists have to suffer through endless phase diagrams in school, supposedly explaining why one obscure mineral appears before another in a rock, only to never use them again.
Glad to see they are of limited use in atmospheric science as well.
Elliptically related topic: Regarding CO2 in ice cores at Vostok: Since some 3500m of ice built up raising the altitude as it did so, is there any indication that the CO2 content sytematically declined as one ascends the record? Was there any sign that the gas at higher pressures down below caused microfracturing and outgassing of the cores?
OT http://www.wrh.noaa.gov/pdt/
Go quickly to the above site and check out the @Apple logo in the infrared over Oregon. I screen captured it when it was really good.
“If C02 is heavier than air, what affect will this have on its “freezing out” of the atmosphere as snow?” Essentially none. The individual CO2 molecules are heavier than N2 and O2 but the molecules collide with other so frequently that for most purposes you can treat the air as having uniform composition.
Yes – an excellent debate. Thanks to Stephen Goddard for the original post as well. He posed a very good question and one which not many of us knew the answer to – me for one.
It was also good to see real science in action.
I missed the fun. Must have been arguing someplace else:).
I was intrigued that in the other thread
http://wattsupwiththat.com/2009/06/09/co2-condensation-in-antarctica-at-113f/
Phil. (00:20:45) :
look at the phase diagram of CO2!
That is four degrees below the freezing point of CO2 and would cause dry (CO2) ice to freeze directly out of the air.
This would only occur in an atmosphere entirely composed of CO2, i.e. a volume fraction of 1.0 not 385ppm. At a vapor pressure of ~1000ppm the sublimation point is approximately -135ºC
One in a thousand will not be shaking hands with a second one to start making snow. Pity. I had that image of ice crystallizing out of clear air, like pixie dust, as sometimes happens when it is very cold and very humid. I suppose it means that the kinetic energy is so low that the gravitational one sticks that molecule on the surface, and then another one from the 1/1000 comes etc etc.
Mars is in a better position and gets CO2 snow.
from the wikipedia article on Mars:
Mars’s mean surface pressure equals the pressure found 35 km above the Earth’s surface. This is less than 1% of the surface pressure on Earth (101.3 kPa). The scale height of the atmosphere, about 11 km, is higher than Earth’s (6 km) due to the lower gravity. Mars’ gravity is only about 38% of the surface gravity on Earth.
The atmosphere on Mars consists of 95% carbon dioxide, 3% nitrogen, 1.6% argon, and contains traces of oxygen and water.[5]
Okay, let me get this straight. You had a hypothesis, tested it, found it not to be true, and so abandoned your hypothesis. What the hell kind of scientist are you?
Hi,
We have just added your latest post “Results: Lab experiment regarding CO2 “snow” in Antarctica at -113°F (-80.5°C) – not possible” to our Directory of Science . You can check the inclusion of the post here . We are delighted to invite you to submit all your future posts to the directory and get a huge base of visitors to your website.
Warm Regards
Scienz.info Team
http://www.scienz.info
jmrSudbury (04:28:31) :
The five pictures from Dr. Thomas Thatcher are not appearing. The links are broken. — John M Reynolds
Check your firewall settings. I couldn’t see them either until I turned off ad blocking. Something about the URL got the pictures labeled as ads.
The photos are not showing due to an error in coding. The closing virgule, “/” in the image markup needs a space before it.
cheers,
gary
the partial pressure of CO2 is the key to the problem.
Yes – it seems that both sides of the debate on AGW seem to have forgotten some basics from high school chemistry. Good on you guys for admitting the error. Everybody makes mistakes after all to err is human.
The people who frighten me most are those who are never wrong and won’t admit it.
Incidentally, have Steig et Al come forward and retracted their Nature paper (for their nonsensical inversion of temperature data that turned cooling into warming)?