The most famous carbon dioxide absorber | Hacker News Reader

The most famous carbon dioxide absorber

howequipmentworks.com

178 pointsbemmu74 comments

Anyone selling house-size CO2 absorbers to keep CO2 in my house to more like pre-industrial 200ppm rather than the 800ppm that's more common of house air in cities?

Not sure what city you live in but in the big cities I’ve lived in it was always easy to get the level down to 500ppm by opening windows.

Yeah I live in Chicago and it is not hard to keep it at 450ppm. Right now it’s 493ppm in here.

I mean that’s really low. If it’s cold outside you’re probable just wasting energy keeping your spaces warm with so much ventilation, making the problem worse in the process.

What are you using to measure this?

(I'm sure I could do my own research, but was more curious since it seems like you've already got a setup.)

Hah! Glad someone else wants to try this!

A HRV or ERV, depending on how humid it is where you live will help immensely. Unfortunately hard to retrofit into existing construction.

The average human exhales about 1 kilogram of carbon dioxide on an average day. Carbon makes up 27.3% of that: ~300 grams. That's the weight of a smartphone.

The logistics would be complicated, average plants aren't going to be accumulating so much mass so quickly. You would need aquariums full of algae. Just isn't worth it.

You'd only need a few hundred grams of triethanolamine if you regenerate it several times a day (with a vent to outdoors), but there are probably some spill risks and maybe mist. Soda-lime is cheaper but requires inconveniently high temperatures to regenerate, which probably result in unwanted emissions requiring mitigation as well as too much energy use. Regular lime (without the soda) avoids the emissions but takes a month to absorb the carbon dioxide. Alkali-metal oxides, hydroxides, and peroxides like those discussed in the article are extremely compact and fast-acting but even more difficult to regenerate. Bioreactors with spirulina or chlorella have been tested successfully but require hundreds of kilograms of algae per person and are finicky, being prone to infection. I think it's eminently possible at a technical level, but at a political level, basically you can only do this kind of experimentation if you live in China.

An actually physically feasible thing you can do is to whitewash some walls. You need to apply about 7kg of whitewash per person per week, so you are going to need a lot of walls, on the order of 400 square meters of wall per person, because the whitewash is regular lime, not soda lime. (If you're daring enough to dope your whitewash with lye, maybe you can get by with less wall area, but you still need to keep applying the whitewash at 7kg per person per week.) You can make them out of plywood, sheetrock, sheet metal, old sheets, whatever whitewash will stick to. After a few months you will need to start throwing out 14kg of fully cured whitewash per person per week, or calcining it to make fresh whitewash. Try to get whitewash with as little chalk in it as possible.

At this small scale, dozens of kilograms per week, you might be able to calcine the used whitewash in a pottery kiln on your patio. Beware that electric kilns generally do not handle reducing atmospheres well. I'm not sure if carbon dioxide would be too much for them. I think it should be fine, but don't blame me if you ruin your Kanthal.

A caution I should have thought to include: if you do this to remove the carbon dioxide you exhale, you need to make sure you have enough ventilation that you don't asphyxiate. In the absence of carbon dioxide to tell you to seek fresh air, you won't notice the oxygen levels dropping; you'll just get stupid, then lose consciousness, then die. Homemade rebreathers have a high fatality rate. I don't think such good sealing is likely at the scale of an entire house unless it's literally underwater or something. But keep it in mind.

I think measuring CO2 is mostly only useful as a proxy for how well you are ventilating (which is correlated to the health of your air unless outside air is filled with ie small particles or smog), and when you measure 800 ppm it is more than adequate. 800 is not doing anything to the body (that we know of).

Do you want to use chemicals and devices that make the climate problem worse just to lower the CO2 concentration in your personal space? Sure it’s a small effect but not something we can all do.

IIRC 1000 is where it starts having easily detectable negative effects on human cognition, which means it has less easy to detect negative effects on human cognition at numbers lower than that.

If you own a CO2 sensor you know that even at 5000 it’s not “easily detectable”… I know what is said about cognitive abilities and CO2 but I guess that’s hard to feel yourself. Moreover I doubt those results. Humans start to die at 10%, that’s (if I’m not mistaken) 100.000 ppm.

Ive had a CO2 sensor for years, take it with me usually. In the beginning I was quite shocked, but I’m starting to doubt all the bad things said about CO2 over 1000-1500 ppm now…

I've found the same. And thinking it through, I can't come up with a mechanism for how a few more CO2 molecules bopping around in a sea of nitrogen and oxygen changes anything about how my lungs exchange the CO2 in my body with air around me. These counts are ppm, nothing!

If there's twice as much CO2 in the air, twice as much CO2 goes from the air into your blood.

CO2 enters the blood in the body, it comes out of the lungs. If you breath too hard you loose too much CO2 and your blood pH will go up. That’s why you breathe into a bag when hyper ventilating, to keep that precious CO2 in.

Air you breathe out is around 40 thousand ppm (and higher during exertion), and the air in the lungs isn't completely replaced every breath - I doubt there's much measurable difference at the actual alveoli at the levels we're talking about. You'll probably get more of a difference if you're breathing deeper and faster, or just got up to get a coffee or similar.

And interestingly there are studies that show that breathing in air up to 3% co2 (30k ppm) "did not substantially impair either cognitive and motor performance" [0]

[0] https://www.tandfonline.com/doi/epdf/10.1080/10803548.2007.1...

High CO2 most definitely impairs cognitive performance as shown in many studies, and also backed up by substantial personal experience.

Double blind personal experience?

Probably way more important than lowering the CO2 is getting rid of PM2.5/PM10.

Rooftops nowadays are best used to mount solar panels. Some system growing circulating algae, be it on the roof or on the sun drenched walls while doable would have way higher at least the operating costs. Clining is one thing. If you live in the area with below zero temperatures either you drain the system or invest even more in some glasshouse, maybe thermal isolation at night or heating.

As mentioned by others, there are chemical solutions.

One can combine chemical absorber solution with electrolysis for the regeneration:

Efficient Direct Air Capture in Industrial Cooling Towers Mediated by Electrochemical CO2 Release

https://onlinelibrary.wiley.com/doi/10.1002/anie.202412697

Honest question: Why would you want to? The average CO2 concentration in your lungs is something like 20,000 ppm, so it doesn't matter much whether ambient CO2 is at 200ppm or 800ppm. Other aspects of air quality do matter, but I'm highly skeptical about the value of capturing CO2 in your house.

Are you not familiar with any of the research linking high CO2 with harmed cognition and harmed alertness? It is manifest at as low as 800 ppm, certainly at 1000 ppm, and personally even at 600 ppm for me. There is good reason to want the preindustrial level that humans lived with for almost their entire history.

Yes, I've seen such research, but I am highly skeptical, to put it very mildly. This actually being the case is simply implausible from the physiological perspective, considering the very high (and constantly changing) concentration of CO2 in the lungs and in the bloodstream. Early research with Navy submariners was consistent with this -- no detectable impairment below 1% (10,000 ppm) and clear impairment at 3-4%. Later long term studies with 0.5% exposure (5,000 ppm) also found nothing. I put the recently popular research showing cognitive impairment as low as 600 ppm in the same mental niche as vitamin megadosing -- underpowered, low quality research with no basis in human physiology.

That said, CO2 can often serve as an easily measurable proxy for stuffy air, which can contain particulates, formaldehyde and other organic exhalations which may actually have some effect (psychological, if nothing else). But this just calls for ventilation and air filtering, not CO2 scrubbing.

It is me who is skeptical of extremely healthy test subjects in their early 20s being used to define what's healthy for the population at large. As for vitamin dosing, there is most certainly an optimal dose and form of each vitamin, somewhere between its lower and upper limits.

Offices have high ventilation but also high CO2, and the effect shows clearly in a meeting room, putting people to sleep.

Many of us knew the story from books, or even the Tom Hanks Apollo 13 film, but the detail here is fascinating.

The triumph of the movie, as described at the time, was making people care about a story they already knew the ending to. Opie sure turned out good.

> The triumph of the movie, as described at the time, was making people care about a story they already knew the ending to.

One could, I think, argue the same about any movie about a historical event. I think that it would seem strange, for example, to say that that was the main achievement of Sands of Iwo Jima.

I think it’s different when you’re talking about an army versus three people in that army.

We don’t know if Private Ryan or any of the other characters make it. We can assume most of the actors make it off the beach at the beginning, but that’s about it.

I mean it was also way better than the first 12 prequels

Also for anyone interested, some of Flight Director Gene Kranz's recordings are available online. Here's the first part: https://www.youtube.com/watch?v=KWfnY9cRXO4

The comments have time stamps for some particularly interesting moments, but the incident occurs 8 minutes in, and the infamous "Houston, we've had a problem" remark happens at 9:20.

The blog post talked about how everything had to be communicated verbally because you could not share images, but since we're so used to Hollywood adaptions or documentaries, I find the recordings really drive the point home.

And there’s also a site with replays of some Apollo missions. Several audio, video and data feeds. https://apolloinrealtime.org/13/mobile/

PSA: Apollo 13 is currently marked as “Leaving Soon” on Netflix.

The scenes where they identify the square peg/round hole problem and where John Aaron and Ken Mattingly get the power draw down are some of my favorite in any movie. Must watch for any engineer

I love how their solution was not to fit the square peg into the round hole, but to use the suit air hose system to pull air through the filter instead.

They achieved the important function ("flow cabin air through the filter") in a totally different way.

https://www.nasa.gov/history/afj/ap13fj/15day4-mailbox.html

https://spacecenter.org/apollo-13-infographic-how-did-they-m...

It's a fun read. It does seem to imply that the parachutes slowed them down from 25,000 mph, but the heat shield smashing through the atmosphere would have slowed them down first.

That would be one helluva parachute.

I don't know of any actual parachutes, but the closest thing is probably inflatable heat shields like HIAD or MOOSE.

https://en.wikipedia.org/wiki/HIAD#Inflatable_heat_shield_en...

https://en.wikipedia.org/wiki/MOOSE

My favorite goal in Kerbal Space Program is not the more common “return from a high gravity planet” or “orbit all the planets in the solar system in one trip” but instead “use every method including atmospheric air breaking, parachutes, and gravity assists, and mining resources /lunar/martian refueling to land a single stage rocket on mars and return”

Most fun thing to plan build and execute in the whole game IMHO

Bonus points if you bring and execute all types of science experiment available. This, and mining to refuel makes SSTO much harder.

*If you find this too easy then an upgrade is to do the same mission, but bring and deploy a permanent base to laythe (fictional moon of Jupiter with oceans). (bonus points if the base is mobile/submersible)

It's worth remembering that this is 1960s technology.

I watched the moon landing as a young kid. On our rich neighbors TV. We didn't have one. I do hope that live to see another one. Not sure as they keep delaying it.

I hope your rich neighbours live long enough to allow you to watch it!

Which, apparently, nobody knows how to replicate today.

Maybe 2030? https://en.wikipedia.org/wiki/Chinese_Lunar_Exploration_Prog...

So... like... it's tough, generally works, and doesn't show you ads. Sign me up!

That's the best part - it doesn't ask you to sign up!

We shake our heads at round vs. square filter in the distant 1970 past, but flash forward 55 years and we have that a very similar situation in the active American space capsules - none of the spacesuits are compatible with any of the other ships.

The Boeing spacesuit isn't compatible with the SpaceX capsule, which was recently an issue with the Crew 9 mission. And neither are compatible with the NASA Orion capsule.

and I thought the most famous carbon dioxide absorber would be caustic potash solution

Myself, I was thinking https://en.wikipedia.org/wiki/General_Sherman_(tree) .

I was thinking ‘Amazon rainforest’ or perhaps ‘ocean’

I was going to guess "trees".

A not-at-all-famous-but-maybe-it-should-be CO2 absorber is azolla.

https://en.wikipedia.org/wiki/Azolla_event

> On July 21, 1969, Neil Armstrong stepped off the ladder of his spacecraft and became the first human to walk on the Moon. The first words spoken by him on the Moon that day are still remembered.

>[img that misquotes Neil Armstrong]

is a hilarious way to start

To be fair, they did not say they were remembered correctly.

Or who remembers them (not the person that made the image)

I believe Neil Armstrong said that is the correct quote, it just dropped the "a" in the transmission.

Until recently I believed that too. However, I came across some discussion which made me realize I was mixing up the sequence. The transmission interruption, which can be clearly heard, didn't happen at that point in the quote; it happened a moment later, after the word "man". The critical part of the quote seems to come through clear. It's more of a linguistic question about how "for a" and "for" may sound almost indistinguishable in Armstrong's accent.

I have a similar accent and we would say it like "furrah-man". For me, the "ah" becomes a lot weaker going into the "m", so I can easily see it.

I'm also intrigued by the idea that it was a flub which he realized instantly (if you listen to the recording):

... step for man <pause> (dammit) ... one giant leap...

There is a whole controversy and analysis about that particular syllable: https://en.wikipedia.org/wiki/Neil_Armstrong#First_Moon_walk

Also, the blog post in the submission omits a major detail: the on-orbit docking maneuvers for the CSM to mate with the LM. A minor detail is that the Saturn V's third stage performed TLI (trans-lunar injection) and it actually impacted the Moon. After this TLI, the LM and the CSM were flying free in space, with a bit of separation, and it was the CSM pilot who needed to turn 180° and nose-in to the LM in order to be in the proper configuration for the hypothetical Moon landing.

It was an unusual configuration for Apollo 13, to say the least, because of course they did not land on the Moon, but also because the "base/legs" part of the LM wouldn't be "left behind" on the lunar surface, so they sort of lugged it around awhile. I don't know the exact sequence of jettisoning that base, but they certainly relied on the LM "head" as a lifeboat and a source of additional life-support functions.

At one point they discussed jettisoning the landing stage of the LM, for less mass so that the PC+2 burn would get them home faster, but most of the batteries and O2 tanks on the LM were in the descent stage (4 of the 6 batteries, I don't remember the distribution of the tanks) so dropping the landing stage made their other problems even worse. The landing stage stayed attached to the ascent stage for the entire life of Odyssey, and was dumped into a deep trench in the Pacific Ocean because there was a nuclear RTG to power the ALSEP attached to one of the legs of the lander.

There is a whole controversy and analysis about that particular syllable

Oh FFS... this guy went to the Moon and all people can argue about is what he said? How far we've fallen...

Be glad people still believe anyone ever went to the moon at all. That may not be the case in a few more years.

Pretty soon it will be possible for tourists to visit the moon and see the litter we left with their own eyes.

In fact, job 1 needs to be building fences around the landing sites so people don't trample all over them.

We're still in the "millionaire celebrity ego-trip to nudge against the Karman line" stage of commercial space travel. "Pretty soon" is nowhere near a likely timeframe for crowds of tourists clomping around on the moon.

The moon is further away than you think. The Apollo mission architecture was a lot more feasible than others that have been considered. The current plan to use a Starship returns about the same payload with a much larger and taller vehicle that is inclined to tip over. You really want a landing pad.

Refueling from lunar materials might be possible but volatiles seem precious. The mission with that vehicle that makes the most sense to me is to land it with a full payload and use it for habitat, workshop, storage tanks or scrap metal.

Space tourism to a micro O’Neill colony in LEO decked out as a flashy space hotel seems more believable to me. I designed one that needs 15 Starship loads of LN2 for the atmosphere but that is fewer launches than they plan to put one Starship on the moon.

Funny thing, I bet by then authentic Armstrong poop (which comprises some of that litter) will be more valuable than moonrocks.

IIRC Armstrong said some years later that he had unintentionally left out the "a".

I never knew this whole story, fascinating. There is a nice intro for my “Interoperability in Healthcare” talks in there. Nice write up!

Wait did they really launch apollo 13 at 13:13 local time lol. I think of myself as not particularly superstitious but that's pushing it.

No. Local time for the vehicle was 14:13. Local time for mission control was 13:13.

The part of story where Co2 absorbers were incompatible between two modules sounds really dumb. What was the cause?

There was never any requirement for sharing anything between the two vehicles and they were made by completely different contractors. Grumman made the LEM and North American Aviation made the command module. There was also a significant redesign of the command module after the Apollo 1 fire which completely changed the cabin environment. Sort of how you probably cannot take a chunk of equipment out of the cockpit of an Airbus 320 and expect to slot it in to a similar role in a Boeing 737.

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