4 ms·

It's probably easier to concentrate oxygen/nitrogen and add them, rather than scrubbing CO2. It's a lot harder to remove a gas than it is to dilute it by adding

It's probably easier to concentrate oxygen/nitrogen and add them, rather than scrubbing CO2. It's a lot harder to remove a gas than it is to dilute it by adding other gases. A home oxygen concentrator can be had for <$1k. The most difficult thing might be reliably monitoring the gas levels to make sure an unsafe imbalance isn't created.

perihelions 5y ago
Scrubbing CO2 is very easy because it is a pretty reactive chemical -- simply spraying air with a strong alkaline solution works. Separating nitrogen is by comparison very involved (it's a cryogenic distillation of liquefied air), and also there's like three orders of magnitude more of it. Check the wikipedia article I linked: this is a solved problem in multiple contexts.
- throwaway09223 5y ago
  I think you're right. I didn't realize how small of a percentage normal CO2 levels were. Thanks for the correction!
Dylan16807 5y ago
Two humans will output a thousand liters of CO2 a day, so to keep that at a low level would require millions of liters of oxygen/nitrogen. Versus several pounds of scrubbing mixture.
- krastanov 5y ago
  No? You use filtered outside air to mix it down to outside levels and only then add concentrated gas (cryogenically separated from the same outside air). It would probably be just a few pounds of oxygen (instead of a few pounds of scrubbing mixture that needs to be trucked in and out).
  - Dylan16807 5y ago
    If you can just flood in outside air then you don't need any pure gas at all. If need pure gas, for example you're trying to avoid losing your air conditioning or you're aiming for sub-ambient CO2, then you can't mix in lots of outside air. For the former you'd need enormous amounts of cooling and humidity adjustment, and for the latter outside air will actually make your job harder. So in those circumstances, the math is very simple. A human outputs X CO2, you want X to be a fraction of a thousandth of the air, you either scrub it or you add thousands of X in purified oxygen+nitrogen.
hollerith 5y ago
You seem to be assuming that the only physiologically-relevant factor is the ratio of O2 to CO2 in the air. I am pretty sure that is wrong: for example, dissolved CO2 makes the blood significantly more acidic whereas dissolved O2 does not make it more basic. Also, the US Navy's submarine service, the Space Shuttle and the Apollo missions solved the problem by removing CO2, not by adding other gasses.

perihelions 5y ago

Scrubbing CO2 is very easy because it is a pretty reactive chemical -- simply spraying air with a strong alkaline solution works. Separating nitrogen is by comparison very involved (it's a cryogenic distillation of liquefied air), and also there's like three orders of magnitude more of it. Check the wikipedia article I linked: this is a solved problem in multiple contexts.

throwaway09223 5y ago
I think you're right. I didn't realize how small of a percentage normal CO2 levels were. Thanks for the correction!

Dylan16807 5y ago

Two humans will output a thousand liters of CO2 a day, so to keep that at a low level would require millions of liters of oxygen/nitrogen. Versus several pounds of scrubbing mixture.

krastanov 5y ago
No? You use filtered outside air to mix it down to outside levels and only then add concentrated gas (cryogenically separated from the same outside air). It would probably be just a few pounds of oxygen (instead of a few pounds of scrubbing mixture that needs to be trucked in and out).
- Dylan16807 5y ago
  If you can just flood in outside air then you don't need any pure gas at all. If need pure gas, for example you're trying to avoid losing your air conditioning or you're aiming for sub-ambient CO2, then you can't mix in lots of outside air. For the former you'd need enormous amounts of cooling and humidity adjustment, and for the latter outside air will actually make your job harder. So in those circumstances, the math is very simple. A human outputs X CO2, you want X to be a fraction of a thousandth of the air, you either scrub it or you add thousands of X in purified oxygen+nitrogen.

hollerith 5y ago

You seem to be assuming that the only physiologically-relevant factor is the ratio of O2 to CO2 in the air. I am pretty sure that is wrong: for example, dissolved CO2 makes the blood significantly more acidic whereas dissolved O2 does not make it more basic. Also, the US Navy's submarine service, the Space Shuttle and the Apollo missions solved the problem by removing CO2, not by adding other gasses.