UPDATE2: The question has been resolved, please see this new WUWT story on the issue. – Anthony
UPDATE: There is a debate raging in comments about the validity of the statement “That is four degrees below the freezing point of CO2 and would cause dry (CO2) ice to freeze directly out of the air.”
On one hand we have an argument from several commenters that says that the temperatures, pressures, and phase diagrams only apply to a pure state of CO2, such as in the manufacture of dry ice.
“Certainly, at least some of the CO2 in the atmosphere at the poles does freeze out (of the air) during the winter.”
So there appears to be a debate. If it turns out the statement is wrong, and some empirical proof can be presented, I’ll retract and/or amend the article. There appears to be a wide interest in this question, so I’m not opposed to find the true answer, even if it means the statement is entirely wrong.
Feel free to post in comments, but leave the snark and ad hom out of it. I’m more interested in settling the question.
I’ve also changed the title to be more reflective of the question before us now. – Anthony
By Steven Goddard
The south pole of Mars (seen below) similarly has an eight metre thick layer of dry (CO2) ice on top of the H2O ice.
Mars, too, appears to be enjoying more mild and balmy temperatures. In 2005 data from NASA’s Mars Global Surveyor and Odyssey missions revealed that the carbon dioxide “ice caps” near Mars’s south pole had been diminishing for three summers in a row. Habibullo Abdussamatov, head of space research at St. Petersburg’s Pulkovo Astronomical Observatory in Russia, says the Mars data is evidence that the current global warming on Earth is being caused by changes in the sun. “The long-term increase in solar irradiance is heating both Earth and Mars,” he said.
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Murffft…. So the “consensus” settles on phase diagrams as Partial Pressure rather than absolute pressure.. OK, then that Clathrate phase diagram would have CO2 / H2O clathrate with CO2 partial pressure of 0.0004 somewhere off the left edge (which I would extrapolate by the sliding finger method 😉 as about -130C so only during a really bad ice age…
George,
Your qualitative ramblings don’t hold water. The stable state of CO2 is quite clearly defined in the phase diagrams at a specific atmospheric pressure.
http://scifun.chem.wisc.edu/chemweek/CO2/CO2_phase_diagram.gif
Mars has less than 1/100 of earth’s atmospheric pressure, so the freezing point is significantly depressed, as seen in the phase diagram.
As far as water boiling goes, the partial pressure of water in the atmosphere is irrelevant. Water boils at the same temperature in Phoenix, Barrow and the Amazon. When the vapour pressure at the surface of the water exceeds atmospheric pressure, it boils. This is completely independent of the composition of the atmosphere. The atmosphere could be pure nitrogen and the boiling point of water would not be affected significantly.
Science is not a democracy and is not decided by consensus.
Mark T (15:48:11) :
Your breath.
Exactly, or even more dramatic, near the exhaust pipe of any combustion engine, generator, boiler, or furnace. These should have significantly higher concentrations of CO2 and could likely lead to CO2 condensation (deposition) at temperatures near -128F.
Or was it -128C? (Why do we American’s insist on non-metric units anyway?)
I think I see where Steve Goddard is getting confused. As George E. Smith points out, boiling is evaporation from inside the liquid, which does indeed depend upon atmospheric pressure, whatever that atmosphere is made of. Evaporation from the liquid’s surface, however, depends on the partial pressure of the liquid and gaseous phases, i.e. the net movement of molecules depends on the number leaving the liquid phase vs. the number entering. Perhaps a good thought experiment would be to compare the evaporation of pans of water in identical sealed terrariums, one of which also has a container of drying agent.
BTW, I bet knowing the vapor pressure of Arsenic over hot gallium Arsenide in a diffusion sealed ampoule makes George very popular at parties! 🙂
wattsupwiththat (14:30:42) :
Give me a couple days – I’d like to try writing up my comments about windshield frost referencing a format like George’s post-from-scratch with the phase diagram. I don’t know if I’ll have time to get to it, George, if you want to do it yourself, great. I think with the two accounts, the familiar water one would be a good preface to the more foreign CO2 at Antarctica case. If I’d do write it, I’ll post it here, not on the article du jour as an OT piece.
There are some neat effects at a boundary between supercooled dew and frost and why there’s a bare strip between the two, but that’s a little outside of the phase diagram. Perhaps that would be a good “But wait! – There’s more!” epilogue.
-Ric
SteveG “”Water boils at the same temperature in Phoenix, Barrow and the Amazon.””
No, it does not. The atmospheric pressure due to elevation is different. You are correct, if you are reading the phase diagram correctly. The freezing point for CO2 is set by the pressure, not the partial pressure. Most interesting point is that waters critical point is oC, and standard pressure. One can have water in all three phases at these conditions.
“”” Ric Werme (16:48:32) :
wattsupwiththat (14:30:42) :
Thank you all for playing “Mythbusters” at WUWT.
Further, since this question has arisen in discussions before, I’m going to write a full post on it, to put it to rest and act as a reference for the next time the question comes up.
Give me a couple days – I’d like to try writing up my comments about windshield frost referencing a format like George’s post-from-scratch with the phase diagram. “””
Ric I’m not super fluent with inputting drawings etc into Anthony’s format like others have done. You may have noticed that absent from my posts.
But I would really like to see how you put it as you see it. I always learn something from other people’s posts, so I’ll let you take the stage and post your rendition.
George
“”” Gary Hladik (16:47:26) :
BTW, I bet knowing the vapor pressure of Arsenic over hot gallium Arsenide in a diffusion sealed ampoule makes George very popular at parties! 🙂 “”
Well silicon process engineers have it very cushy dealing with an elemental semiconductor. The problem with the III-V compounds such as gallium arsenide, is that they are chemical compounds and as such, at elevated temperatures as in a diffusion step, they actually can dissociate and that can wreck a crystal surface that you are trying to make diffusions into.
A dopant source such as a Gallium zinc alloy works fine at low diffusion temperatures, but it cannot easily make high concentration layers at those lower temperatures. But if you use a dopant like zinc arsenide, then it completely dissociates and evaporates, and maintains an arsenic overpressure that stops the crystal surface from decomposing. The vapor pressure of Arsenic over Gallium arsenide is almost one atmosphere at the melting point of Gallium arsenide; so you can diffuse it in a sealed ampoule, with Zinc Arsenide, and not blow the ampoule up.
We had many hundreds of Kg of high purity Arsenic in our building growing about one Kg GaAs single crystal ingots (for LED substrates); more than enough to poison every thing in the known universe; and likely some of the parallel ones too. In 12 years of operations we never once had a single employee ever test positive for arsenic contamination; and every single one who worked with it was tested every month. But the real problem was the Arsine in Hydrogen gas used for growing epitaxial Gallium Arsenide Phosphide on the GaAs wafers. It smells like garlic; which is an odor you never want to get around an LED operation.
No Climate consequences of Arsine that I am aware of.
Well, let me add to the muddle.
The y-axis of the phase diagram Steve links to is the absolute pressure of CO2, not the total atmospheric pressure. To expand on dearime’s, George’s, Ric’s (and others’) point, let’s think of it in terms of the water phase diagram.
http://www.pgfreezedryingconsult.com/subweb/water_phasediagram.htm
Frost does not automatically form when temperatures are below freezing, but when the surface temperature falls below the dew point (or frost point) of the air. Similarly, water vapor doesn’t automatically condense even though the temperature is below the boiling point. While it’s true that you can get water to condense at room temperature by increasing the total pressue, this only happens if the absolute pressure of the water exceeds the saturation pressure. For example, if we have humid air at 90% relative humidity, this obviously means the air has 90% of the water level needed to be saturated. If you pressurize the humid air to 2 atm, all of the pressures double, including that of the water vapor. It theoretically would be 180% of its saturated level (or approximately so), except that it condenses out. But it still has to be above it’s equilibrium absolute saturation pressure. Indeed, if the relative humidity of the ambient air was 25%, compressing the air to 2 atm would not cause the water vapor to condense, since it would now only be at approximately 50% relative humidity.
As others have mentioned, at 380 ppm (0.00038 atm), you have to go quite low to condense solid CO2, even if the total pressure is 1 atm. Even if it were to condense from a localized high concentration, it would be no more persistent than someone’s frosty breath on a cold morning.
Sorry if I’m repeating what’s already been written. It was a bit tough reading through all the comments.
edit
But it still has to be above it’s equilibrium absolute saturation pressure to condense out .
Uh, sorry i’m not reading all your blog, ‘cuz I’m dying of duhcanser and i have better things to do . . .
[off topic, badly]
Actually, the III-V compounds can give us a different input on the H2O versus CO2 situations.
As I said above the saturation vapor pressure of Arsenic over molten gallium arsenide (at the melting point), is slightly less than one atmosphere; so you can safely grow single crystal GaAs by variations of the Horizontal Bridgeman process such as Gradient Freeze; and you can if you want do open tube diffusions into GaAs somewhat below the melting point of course.
On the other hand, Gallium Phosphide has a vapor pressure of Phosphorous at the melting point, that is around 40 atmospheres, so you can’t grow single crystals of GaP in any atmospheric pressure vessel, and it is typically done by encapsulating the melt under Boric Oxide molten glass (so you can see through it) in a high pressure vessel (bomb) at about 45 atmospheres pressure.
That is similar to the CO2 case where you need over five atmospheres of CO2 pressure to have stable liquid CO2.
Lots of good stuff here. Thanks again for the review.
We have first-hand evidence that CO2 does condense out of the
atmosphere on LNG tankers.
We all know about CO2 snow equipment — you can make
CO2 snow anywhere on earth on demand from a high pressure
cylinder.
Water/C02 snow is possible, and that is CO2 condensing out, but
not by itself.
2000 years ago the Romans used clever engineering and radiational
cooling to make ice by condensing and freezing water out of the air —
in North Africa.
My guess is a similar setup/experiment in the Antarctic with CO2
would condense to a solid. Consider a pool of CO2 formed by a
3 meter square of sealed 2″ expanded styrene, with walls 1meter
tall. Shielded from the warming earth and exposed only to the
cold of space, would the crystallization happen? Good setup might
give a 25K cooling (SWAG), and that might be enough.
Does Mythbusters do on-site research?
@Phil, thanks for your postings on this thread. It is important that the science comes first, not people’s egos. If folks don’t like being robustly questioned on their hypotheses then they should not be posting on a website that has an agenda of questioning other theories. Indeed, Phil, your obvious correctness should vindicate the vociferousness of your posts.
REPLY: There is never an excuse for rudeness. – Anthony
Steven Goddard (13:01:22) :
The point is that Antarctica is freaking cold, and that if Abdussamatov is correct, Mars’ polar ice caps should either be growing or have slowed down their wasting. Why do people get distracted so easily?
With all due respect. You did the distracting Steve
Mt Kilimanjaro, the ice is disappearing yet it never gets above freezing. Sublimation.
I would think the same probably applies with CO2 at the Antarctic.
Doesn’t detract from the point about whether the South Pole on Mars is refreezing, just you shouldn’t have mentioned it.
DaveE.
Goddard fired from the hip with his comments about the overall atmospheric pressure determining the transition point of CO2, rather than the individual partial pressure. He is fundamentally wrong. This is basic junior year P-Chem. Even in some cases, basic first year chemistry. It’s sad that he fired from the hip in defending himself this way. [snip ]
I just put this to my software guy who has a degree in physics and used to work in hi tech manufacturing industry. He reckons it is total atmospheric pressure that counts not partial pressure of CO2.
So he thinks Steve Goddard is correct.
Now can somebody please do the experiment? This discussion is too much like arguing about how many angels can fit on the head of a pin.
Experiment? Well, I have a freezer that maintains -80˚C (-112˚F) in my lab, and it can be set as low as -86˚C (-122˚F).
I can already tell you that dry ice placed in the freezer at -80˚C will sublimate, although much more slowly than at room temperature, of course, because I’ve done it many times. I can also tell you that the snow from the freezer does not “pop” when thrown in water the way that dry ice does, but this is an admittedly poor test.
It should be relatively trivial to find 5 or 10 scientists with ultra low temp freezers, and place a weighed cup of dry ice in them to see what happens. I’m willing to do this, although to do it properly would require setting the temp down to -86 in the morning, then placing a weighed cup of dry ice in at at the end of the work day, so the internal freezer temp won’t be disturbed by people opening it up. So I wouldn’t have an answer until 10AM EDT Friday.
But, from my past experience, this is unnecessary. The freezer manuals do not warn about the hazards of CO2 accumulation in the freezer, and I have never, in 20+ years of life sciences research, seen anything that looks or acts like CO2 snow. (I can tell you, however, what happens if you put a glass 20oz bottle of diet coke in the freezer to chill it, and then forget it’s there. It’s not pretty.)
In fact, I’m rather embarrassed that I did not think of this rather obvious answer earlier. I’ll run the experiment if you want.
REPLY: Hi Tom, Yes we’d love to see it, especially if you can take a photo or two along the way. Thanks for your kind offer. – Anthony Watts
Frank, if you open a tank of liquid CO2 at room temperature and pressure, you will get dry ice formation as the heat of vaporization drawn out of the CO2 by the fraction that evaporates lowers the temperature of the remaining liquid.
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.
So 1 m^3 of freezer space contains 380 cm^3 of CO2, ignoring colder => denser, this is approx .38/22 moles of CO2 @ur momisugly 44g / mol, ie. 0.76 grams .
As a quick bodge temp correction multiply by 300K/180K => 5/3 so I’ll offer 1.25g per m^3 as max achievable CO2 frosting.
I’d be interested to know how you’ll get all the frosting to occur on the CO2 block?
An experiment would need to mimic the thermal gradient. -70C on one
side, behind a good insulator, and 4K on the other side. (Space).
What is the apparent sky temperature above a good insulator at the
south pole? It has to be considerably lower than -70C, otherwise the
ground would heat up. If somebody knows the night sky temp. at
the south pole, we can get a good idea fairly quickly. Just consider
the CO2 gas gravity-trapped in the pool to be a perfect black body
radiator with zero heat capacity. How cold does the gas get? Cold
enough to solidify?
No partial pressure need be considered at this point. A post above
noted that CO2 does condense out of the atmosphere in really cold
cases. (LNG tanker)
This will not be easy to model in a lab. The thermal gradient is too
steep. I cannot think how I would model the radiational cooling
frosts we get here in SoCal. It might be 75F during the day, but in
winter when it gets down to 35F on a clear night, well-insulated
roofs freeze, as will tall lawns. Pavement, even inches away,
does not freeze or even get really cold.
I have not read all the responses, so if I am repeating someone, excuse me. I can assure you that the gas, even in small partial pressures, could freeze directly out and accumulate if the temperature were cold enough on Earth. However, the partial pressure of CO2 is so low on Earth (0.3 torr at sea level) that the equilibrium point at sea level (where it would accumulate for even a slightly lower temperature) is about -140 C (-220 F). At higher altitude, it is even lower. Thus CO2 will NOT accumulate at any temperature found on the poles. The problem is that- if the frozen CO2 vapor pressure is above the CO2 atmospheric partial pressure, the gas cannot accumulate on a surface because the sublimination rate would exceed the condensation rate. Mars has a partial pressure about 5 torr CO2, so can freeze and accumulate at local temperatures below about -80 C (-140 F), which do occur at the Mars pole.
My bad,
The Mars pressure would require -122 C or lower (-187 F). I slipped up looking in the table. The Earth case is correct.
I think a comment is needed to reply to several posts. It is only the CO2 partial pressure that matters for balance between condensation and sublimation. The total pressure does not matter.