We are, of course, talking about miniaturizing a Direct Air CO2 capture system, which usually operates at large scale to get efficiency. Replaceable cartridges that are regenerated at a central location may be a better option.
But oxygen concentrators are small and cheap and portable and don’t require much energy to operate.
At 1400ppm CO2, we've turned what, 1000ppm O2 into CO2 (is it 1-1?), or 1% of the atmosphere. Dropping O2 from (Edit: Fixed numbers) 21% to 20%. Or about a 5% reduction in O2 density. Equivalent to approximately 1500 feet of elevation... That's just not that much.
(There's also a long list of papers showing issues with CO2 toxicity at low levels of CO2... I keep intending to write a blog post summarizing them)
1400ppm is 0.14%. Earth's current atmospheric co2 level is around 400ppm, or 0.04%. While the jump from 0.04% to 0.14% might seem significant (3.5x more co2!), it's not.
Submariners survive on 3400 to 11300 ppm co2, or 0.34 to 1.13%:
> Submarine crew are reported to be the major source of CO2 on board submarines (Crawl 2003). Data collected on nine nuclear-powered ballistic missile submarines indicate an average CO2 concentration of 3,500 ppm with a range of 0-10,600 ppm, and data collected on 10 nuclear-powered attack submarines indicate an average CO2 concentration of 4,100 ppm with a range of 300-11,300 ppm (Hagar 2003). [0]
[0] https://www.nap.edu/read/11170/chapter/5
I'd like to emphasize that the average CO2 concentration for submariners is 4,100 ppm or 0.40%, or ten times Earth's current CO2 level.
Oxygen is much more toxic than small amounts of CO2. Pure CO2 will kill you quickly, pure o2 will kill you slowly.
> (There's also a long list of papers showing issues with CO2 toxicity at low levels of CO2... I keep intending to write a blog post summarizing them)
I'm interested.
2) Don’t doctors provide severe COVID patients with pure oxygen? If it’s toxic, why would they do that?
3) How does pure oxygen kill you? What’s the mechanism?
Pure CO2 will knock you out in 4-6 breaths, and cause your expiration in 10-20 minutes. Laboratory animals are routinely euthanized with co2 [0]. Pure O2 will cause your expiration in 4-6 days through the accumulated damage of reactive oxygen species.
[0] "Expose the animals to CO₂ until complete cessation of breathing is observed for a minimum of 2 minutes (a total of approximately 5 to 10 minutes is usually required)" - https://www.bu.edu/researchsupport/compliance/animal-care/wo...
> 2) Don’t doctors provide severe COVID patients with pure oxygen? If it’s toxic, why would they do that?
This is bad medicine. Early 20th century medical investigators figured out best practices for oxygen support, but the insights got forgotten, now they're just in the old papers in the libraries.
> 3) How does pure oxygen kill you? What’s the mechanism?
tl/dr: Hyperventilation.
Oxygen is highly toxic to the cells in the human body, but not generally under standard atmospheric pressure. Breath pure oxygen while >33ft below water and you’ll quickly experience oxygen toxicity, ultimately leading to death. Yes, that’s generally specific to divers, but even pure oxygen at standard atmospheric pressure can have health impacts.
More information: https://en.m.wikipedia.org/wiki/Oxygen_toxicity
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> I'm interested.
Well I don't have a blog post ready to go yet, but I can point you to some papers now.
- This review cites a bunch of papers about health effects in the 1-10k ppm range: https://www.nature.com/articles/s41893-019-0323-1.epdf?refer...
- Table 3 in this paper references a bunch of papers around 10kppm: https://www.researchgate.net/profile/Susan-Rice-3/publicatio...
- These papers show mental effects in the 1-4k ppm range:
https://ehp.niehs.nih.gov/doi/full/10.1289/ehp.1104789
http://www.aretas.ca/sites/default/files/imce_images/Indoor%...
- These two are from nasa about the ISS - which brings it's own complications but otherwise also show mental effects in the above range
https://web.archive.org/web/20190613133240/https://ston.jsc....
As someone pointed out in a reply to another comment in this thread, oxygen is especially toxic 33 feet below the surface of the water (because of higher pressure), but can have toxic effects at the surface too. I don't grok respiration yet, but my understanding is that altitude/pressure is essential for putting the relative N2/O2/CO2 partial pressures into context.
Dry air is ~21% oxygen by volume.
I'm getting the density numbers from here by the way if you want to check the rest of my math: https://www.engineeringtoolbox.com/air-altitude-pressure-d_4...