I see that the coldest recorded temperature in Antarctica is -89.2C at Vostok Station. I also see that the melting point of carbon dioxide is -78C. So… Has it ever snowed carbon dioxide in Antarctica? Is the partial vapour pressure of CO[sub]2[/sub] high enough for this to happen? Are there CO[sub]2[/sub] clouds?
Great question. I cant wait to learn more.
In the late 1980’s I believe some drops of Co2 flew from the sky in Antarctica in the form of crystal snowflakes. There was a group of scientists from Denmark who captured a single snowflake when the temperature dropped below the melting point.
This being the Dope, I’ll point out that -78C isn’t the melting point of CO[sub]2[/sub] at atmospheric pressure.
The dew point of dry air with 300ppm of CO2 is around -258F (-161C) - so that is the temperature you will need to get CO2 snow at 1 atm (14.7psia). With say 400ppm of CO2 that temperature will change to -256F (-160C).
The above temperatures are with accuracy of commercially available thermodynamic packages of air and CO2. to be more precise : Peng Robinson
Now, at the temperature you mention: -128.6F (-89.2C), the water based snow may have around 100ppm of CO2 but it will have an order of magnitude nitrogen more than CO2 - so to call it CO2 flurries may not be right.
1> So… Has it ever snowed carbon dioxide in Antarctica?
Not likely. Unless there was a lot lot more CO2 in the earth’s atmosphere or it got really cold to below -150C.
2> Is the partial vapour pressure of CO2 high enough for this to happen?
This being the Dope, there is vapor pressure and partial pressure. I think you mean to say, did the partial pressure of CO2 exceed the vapor pressure, and the answer to that is no at -89.2C
3> Are there CO2 clouds?
On Earth ? Not as far as I can think of.
Might not be type of cloud the OP had in mind, but there have been instances of suffocating ground-hugging CO2 clouds being emitted by lakes that are on top of volcanic areas.
That is very true - but its still not a cloud in the sense that there is no CO2 condensation - CO2 stays near the ground since it is heavier than air. Incidentally, Mammoth lakes in California has this CO2 issue too - see here
This being the Dope, I’ll point out that the base at the South Pole is high enough that the air pressure is well below one standard atmosphere, at a quick search about 70% of nominal sea-level pressure.
So it’s even more difficult to get CO2 snow.
This being the Dope, there are actually all sorts of authorities who use the term “vapor pressure” to mean “partial pressure”. To quote some of the latter:
David R. Cook, Climate Research Section, Environmental Science Division, Argonne National Laboratory:
“Relative humidity is the ratio of vapor pressure to saturation vapor pressure.”
Peterborough Operating Department Practitioners, UK:
“Water molecules in the gaseous form also exert a partial pressure. This partial pressure (PH2o) is sometimes referred to as the vapor pressure of water.”
Vermont State Colleges:
“The partial pressure due to water vapor is called the vapor pressure”
There are even more authorities who use “vapor pressure” as a shortened version of “saturation vapor pressure”, so I would have to agree with what I think you imply, that this is the most commonly accepted definition. But usage is certainly varied among polite company.