[condiment]

At current rates of emissions, we’re only about 20 years away from people needing to install CO2 scrubbers in their homes.

Soda lime, or calcium hydroxide, is the current state of the art. We use that in an anesthesia and in saltwater aquariums and in scuba rebreathers. An idealized system can capture 500 mg per gram, but in practice you only capture around 250mg/g. This outperforms the method in the article but it’s one-shot. There are interesting proposals to use this for direct capture at industrial facilities and to turn the waste material into bricks for building.

The key advantage of this new material appears to be that it can be heated and reused. That would be very valuable in an interior direct air capture use case. Think about filtering the CO2 from an office or a home to get us back to pre-industrial levels indoors.

[_yb2s]

I think it’s little appreciated that high CO2 levels cause cognitive impairment, and with the same amount of (often very poor) air exchange, higher outdoor concentrations can push indoor spaces to levels that cause impaired cognition and poor sleep. I’ve already been seeing this in my home, and will often open windows even when cold just to keep co2 levels reasonable. One solution that can help is an external air heat exchanger, which can exchange air with the outdoors without compromising your homes heating and cooling like an open window will do.

Noticeable cognitive impairment starts in the 700-1000ppm range, whereas it is very common for homes to reach 2000-3000ppm, especially when in a closed bedroom.

[wcoenen]

> Noticeable cognitive impairment starts in the 700-1000ppm range

The US navy failed to detect such effects in submarine crew, even at much higher levels like 10,000 ppm.

Another reason to be skeptical is that exhaled breath is 4% CO2 (40,000 ppm!). Therefore a few thousand extra ppm in the inhaled air should not make much of a difference to the homeostasis mechanisms in our bodies.

[progbits]

See my sibling comment for meta-analysis that disagrees with you. Would love to see citation for those navy experiments.

[wcoenen]

Citation for a 2018 study with submarine-qualified sailors: https://pubmed.ncbi.nlm.nih.gov/29789085/

[hinkley]

Have you ever met a submariner? These are not normal humans. That’s some serious cherry picking of data.

[hinkley]

Back in the 00’s I worked at a place where we were still ignoring WLB and would work until seven a couple nights a week on average. But the building AC shut off at 6. A few of us noticed that the later it got the worse our decisions and the worse the bickering and we eventually got to the policy that anyone could declare Deciding done for the evening when they realized we were just tired, hot, and stuffy. Every minute past about 6:15 got worse, particularly in summer.

I’m sure the CO2 was part of it but lack of circulation also means increasing temperature, especially with a bunch of people in a small meeting room. Long meetings themselves are a problem and any excuse to call it early is probably worth it even if it’s not entirely true.

[_yb2s]

I don’t need to look at studies in other people, I notice and feel the effects directly at high CO2 levels, such that I can tell when it it too high before checking the meter.

I’d need to look at the study, but I also suspect the submariners would be used to high CO2, and also not experienced enough in doing focused creative or knowledge work for impaired abilities there to be detectable.

[Ey7NFZ3P0nzAe]

Med resident here.

Please consider the possibility that you can accurately detect increased CO2 (it increases your breathing rate almost instantly for example) without it causing impairement.

[_yb2s]

Even if you are right and there is no objectively measurable impaired abilities, the things I can detect directly are themselves extremely undesirable.

I feel irritable, and fatigued/sleepy when CO2 is high. Increased breathing rate by itself activates an undesirable sympathetic nervous system response, that anyone can notice immediately with deliberate breathwork.

Also, it seems likely to me that the same poor air exchange that leads to high co2 causes respiratory disease to spread more rapidly, and with a higher initial viral titer.

[nehal3m]

>One solution that can help is an external air heat exchanger

I have one of those, it blows fresh air in through the bedroom and sucks it back out through the kitchen (loft house, this route prevents food smells from wafting into the bedroom). Aside from just feeling fresh all year, this system also prevents mosquitoes from entering in summer while still allowing air circulation, it automatically bypasses the exchanger at night to provide cool air and it has some pollen filters installed which helps with hay fever.

So great economic return and a bunch of upsides, but it does require space for the exchanger and the ducts throughout the house.

[mrspuratic]

This. I have that type (regenerative MHVR) installed in the attic for upstairs, and a synced pair of in-wall ceramic (recuperative) types on opposite sides of main living area downstairs (eliminating ducting, albeit with reduced efficiency). I haven't attempted any energy/ROI calculations but fresh filtered air, lower humidity and good nights sleep are well worth the claimed single-digit watt power usage to me.

[hinkley]

I suspect bathrooms aren't big enough to buffer the air pressure but it seems like we should design the air handling so the “fan” is always on in the bathrooms. Maybe a split between several places and taking a bit from the cold air return for the rest.

[nehal3m]

The system is always on and moving air as a whole, and the water closet and bathroom have an intake duct that sucks in humid air that goes to the heat exchanger for exhaust. I have a little humidity sensor hooked up to Home Assistant that kicks the fan in the exchanger into a higher gear and returns to auto when humidity returns to baseline.

All rooms in the house have an intake or exhaust duct depending on requirements.

There is also a small control panel next to the thermostat in the living room that controls the whole system for when, ahem, your number two's are particularly odorous (or you're using the kitchen to cook for 6).

[cassepipe]

I have been monitoring for high CO2 for a few months now. I easily find myself in the 1000 - 1400 range for some time before I finally let some air in in winter.

I have not noticed significant cognitive impairment (not saying it did not happen)

[ProllyInfamous]

My quality of sleep/life have greatly increased since installing an Energy Recovery Vent (ERV) — it exchanges outside/inside air through a membrane, which is about 60-80% efficient for both humidity and temperature re-capture (depending on fan speed).

[•] <https://en.wikipedia.org/wiki/Heat_recovery_ventilation#Ener...>

I use a Panasonic model — readily available from Big Box Retail (~$700 + $100 in vent/conduit) — which can do 20 - 60 cfm (in my 900 sqft home this can easiliy exchange the entire volume several times per day).

[ctoth]

> higher outdoor concentrations can push indoor spaces to levels that cause impaired cognition

I am somewhat skeptical of this:

https://www.astralcodexten.com/p/eight-hundred-slightly-pois...

[thangalin]

> I think it’s little appreciated that high CO2 levels cause cognitive impairment

Have you been telling representatives? Here's a letter I wrote to mine:

https://pdfhost.io/v/bRJEGptatL_climate-change

[ifwinterco]

This is a meme on hacker news that's usually stated as a fact, but I'm not sure there's any robust evidence of cognitive impairment at <1000ppm

[progbits]

https://www.sciencedirect.com/science/article/pii/S036013232...

> In this study, a systematic review and meta-analysis of fifteen eligible studies was performed to quantify the effects of short-term CO2 exposure on cognitive task performance.

> The complex task performance declined significantly when exposed to additional CO2 concentrations of 1000–1500 ppm and 1500–3000 ppm

[ifwinterco]

It looks like there might be a very small effect starting at around 1000ppm but so small that many studies find no difference at all, and reliable effects are only noted at 3000ppm or more.

So we're a long way from needing to scrub co2 from the atmosphere to get any work done

[_yb2s]

Not everyone in a population will be affected the same by the same conditions, and the constraints of peer reviewed research make them often a poor choice for guiding personal decisions. By the time you have conditions bad enough to statistically prove harm in a large population, you’re likely already way past causing harm worth preventing in some subset of the population.

[progbits]

Not from atmosphere but we need good ventilation. Over 2000ppm in offices is very common.

[codeulike]

Additional

[lokar]

Really? Wow, I try to keep my place at 500-600, without that much effort.

[malfist]

I find it extremely unlikely that homes are routinely at 2000-3000 ppm. That is extremely high and would mean multiple people in a small area with no air exchange for a long while.

I monitor my indoor co2, but don't take any action because it's extremely rare to be above 700 or 800. I can only remember a handful of times its reached 1k ppm. And my house should be prime candidate for co2, it was built during the era of "seal all air gaps" but before ERV or HRVs. I also use pressurized co2 to inject co2 into a planted aquarium. And my dogs are terrified of open windows so they are rarely open.

[mapt]

It happens a lot in efficient houses that don't cover all bases with HVAC (the vast majority of recently built houses), where the room door is closed, maybe the vents are not ideal, and there is usually no makeup air or forced air ventilation other than a furnace intake.

This change in scientific literature actually causes a ~quadrupling of recommended airflow ratios for tight homes versus ASHRAE's previous guidelines, putting strong emphasis on an ERV. Previously, ventilation needs tended to be dominated by air quality and smell, by humidity buildup, or by theoretical house parties that maxed out the system.

This ventilation adds capital expense, but it's substantially more controllable and significantly cheaper in the long run in colder climates than 'just open a window' or 'just don't build the house so tightly sealed'. Reserve the operable window for the aforementioned house party, which is out of a reasonable design envelope.

[jhpankow]

Homes in the upper midwest are well-sealed and insulated. Bedrooms can hit 2,000 ppm with two adults sleeping in them.

[stavros]

My bedroom regularly gets to 3000 at night, and the flat in general is around 2000. This is in the winter, when I don't open the windows for days because of the cold. The flat is very well insulated.

[cassepipe]

If we are three in my small living room in winter (around 20m2), it easily climbs above to 2000ppm in less than an hour

[deadbabe]

Ok this sounds like BS, what kind of sensor is being used to get such readings? What do you use?

[bluerooibos]

I used an Awair Element after wondering if Co2 buildup was causing my groggieness in the morning and an ever so slight dull headache.

My bedroom was quite small at the time, but I measured the same effect of buildup in a larger bedroom, just the Co2 level took a little longer to reach it's peak.

In the small room it took about 45 mins to climb to about 1400 after I closed the door and went to sleep.

I'm currently trying to install some above-door vents to improve circulation but this is a topic most people don't consider at all, even though studies have shown the effects of classrooms having high Co2 concentrations on exam results and cognition.

[lawrenceduk]

We monitor air data quite closely at work.

CO2 rises really fast with people in even a large space.

I wouldn’t put too much effort into vents above a door as we’ve seen that CO2 will leak through doors and even floors/ceilings very quickly.

[bluerooibos]

> I wouldn’t put too much effort into vents above a door as we’ve seen that CO2 will leak through doors and even floors/ceilings very quickly.

I'd like it to vent out into the hallway and the rest of the apartment though, so not sure what you mean by it leaking through doors? It's obviously not leaking enough, hence the addition of a vent. It's either that or keeping my door open all night which isn't feasible due to noise by other family members waking up etc.

[deadbabe]

When was it calibrated?

[alsetmusic]

I've been using Netatmo stations in each room plus one outside for a decade. They monitor temp, CO2, and humidity. My CO2 levels were nightmarish during wildfires in my part of California across multiple years. Of course, the air tasted horrible and it was absolutely evident how bad it was just breathing two different years so it was not at all surprising to see that correlated on instruments that I check multiple times every day.

Edit: missed a letter

[_yb2s]

I'm using a desktop CO2 meter, they're cheap and accurate, and can be tested by just putting them outdoors and confirming that they read known outdoor levels correctly. What you are saying is not unlike doubting that it's possible to measure temperature with a thermometer- CO2 measurement is extremely reliable, cheap, and mature technology.

This is the meter I am using, costs $39, and is a calibrated instrument with +/- 3% accuracy. I have an academic colleague that uses these same devices for scientific research on plant metabolism, and they are highly accurate and are optionally self calibrating just by opening a window or putting them outdoors.

https://www.co2meter.com/collections/indoor-air-quality/prod...

[ekianjo]

> high CO2 levels cause cognitive impairment

Sounds seriously unlikely. How would this work in practice, at the level of bodily functions?

[_yb2s]

Why would this be unlikely as a prior? High CO2 changes your blood chemistry and breathing rates. Different breathing rates have a well understood effects on lots of systems including sympathetic/parasympathetic activation. There is no reason to expect humans to be evolutionary adapted to CO2 levels that we couldn't have experienced historically.

Several other posters in here have posted peer reviewed studies replicating these effects, but personally I find individual direct experience with my own body to be massively more generally useful when making health decisions than studies in other people, or some known mechanism.

[MathMonkeyMan]

I don't know the mechanism, but: https://www.google.com/search?q=co2+cognitive+impairment

[ekianjo]

This has the hallmark of confounding factors. There is no way you can design a study to control for CO2 alone vs other trace contaminants in the air.

[_yb2s]

In that case it wouldn't matter much to an individual making personal decisions about their environment. Either way, an environment with enough outdoor air exchange to keep CO2 low would avoid these effects.

But hypothetically, what other trace contaminants would you expect to be so universally correlated with CO2 in different environments that they could account for repeatedly observing these effects in different studies? That seems implausible.

[ekianjo]

There's tons of things in the air. Dust (and many different types of dust at different levels, both in contents and size), other gases at the trace level - lack of ventilation not only increases CO2 levels but everything else, too. And then there's the people factor. Who says that people who have proper ventilation and CO2 control are the same as the ones who don't?

If they really want to do a robust study they need to do an intervention study with clear levels of CO2 accurately controlled and the rest of the air being identical for everything else, otherwise it's purely meaningless. (it's doable, by the way).

[marcosdumay]

> The ease of releasing CO2 is the key advantage of the new compound.

I have no idea why the journalist that wrote this article choose to highlight the carbon density of the sub-header. It's almost completely irrelevant for carbon capture plants.

Another clear benefit is that it's a liquid.

Today people mostly use the substances that you called non-reversible in research plants (AFAIK, all plants are research right now). They are perfectly reversible, but that uses a lot of energy.

[nine_k]

> perfectly reversible, but that uses a lot of energy

Looks like a perfect match to a solar plant, which provides basically free energy periodically. All you need is a large enough cistern to hold the liquid during night time.

[marcosdumay]

Yes, it's a great match to solar plants.

But you don't need to store the capture medium. You use a bit more energy to make they work faster while the Sun is shining, and stop everything when it's gone.

The largest bottleneck is what you do to get rid of the CO2.

[eisfresser]

We use the CO2 to synthesize methanol with the H2 we electrolyze using surplus solar energy. The methanol we burn in winter for heat. Yes, that releases the CO2 again. The goal here is not to save the planet. It is to bring solar energy to winter. My house produces many times the electricity that it needs per year, but most of it is wasted in summer. Efficient conversion is not a factor. If I can get 20% of the energy input back as heat in winter, it is worth it: that is oil or wood I don't have to burn for heat.

[nine_k]

I mean, you have to recycle the CO2-carrying liquid. You have to store some of it that has CO2 captured but not yet recycled because the Sun is down.

[netcraft]

160F, non toxic, this already sounds like something that could feasibly be used in the home. I would already be interested in installing one. And would absolutely love to see what it would do to school performance.

The hard part is capture and disposal.

[yodon]

Do you have a citation for that 20 years estimate?

[marcosdumay]

https://gml.noaa.gov/ccgg/trends/

Extending the current exponential for 20 years, we get into the 500ppm region.

I don't think that's enough to need scrubbers.

[Ringz]

Indoor is always higher ppm (how much depends on many parameters) without proper ventilation. „Proper“ should include a „Heat exchanger“ thus you don’t need to reheat fresh air.

[marcosdumay]

Still, it will add some 80ppm over the amount you have today. There's a huge amount of disagreement over how much CO2 is harmful, but it tends to happen over numbers way above 800ppm.

If your room has 2 times the open air concentration, and you are concerned if it's 2.0 times or 2.2 times, you should already be dealing with the problem.

[literalAardvark]

It's not way above, it's around 700+.

So at 500 external you'd pretty much need continuous ERV but not necessarily scrubbers just yet.

[mort96]

According to https://www.co2meter.com/blogs/news/carbon-dioxide-indoor-le..., at 1000 ppm people start getting drowsy. Let's assume that a decent indoor environment has 300 ppm more CO2 This means that our threshold for when people start getting drowsy even in decent indoor environments is when atmospheric CO2 reaches 700 ppm. For reference, it is currently around 420 ppm, and pre-industrial levels were 280 ppm.

From https://www.climate.gov/news-features/understanding-climate/..., the pessimistic projections suggest that we may reach our 700 ppm threshold by roughly 2070; 45 years from now. (The graphs are hard to read precisely)

The 300 ppm offset compared to the outside air is naturally just an arbitrary number, everything up to 1000 ppm (meaning everything up to 580 ppm more than atmospheric levels) is considered "acceptable". That means any increase in CO2 concentration will take an indoor environment which used to be considered "acceptable" and make it cross the threshold into "unacceptable". An indoor environment which would've been at 900 ppm around the industrial revolution (280 ppm) would've crossed the threshold when we surpassed 380 ppm (which was in 1965 according to https://www.statista.com/statistics/1091926/atmospheric-conc...).

let's compare the past 20 years. In 2004, the concentration was ~377 ppm. That's 47 ppm lower than what was in 2024. An indoor environment which was "borderline but acceptable" at 955 ppm CO2 in 2004 would've crossed the arbitrary 1000 ppm threshold by now, and therefore would benefit from a CO2 scrubber. The next 20 years will likely have a higher increase than the past 20 years, so there will be a larger range of currently acceptable indoor environments which will cross the 1000 ppm threshold by 2045.

TL;DR: It's complicated, 20 years is arbitrary, but as CO2 concentrations increase, indoor quality gets worse so indoor environments which were already bad will become worse. 45 years is a more realistic estimate for when your typical good indoor environment will become unacceptable, but it's a gradient.

[netcraft]

I was also a bit skeptical, but chatgpt gave a pretty good answer I think: https://chatgpt.com/share/69553e26-ea28-8011-bc17-8658fbea4e...

Buildings with higher people/sqft could already take advantage of indoor co2 scrubbers today.

[idiotsecant]

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

Just extrapolate.

[jiehong]

Could something like this be used to make cement?

Imagine capturing CO2 to turn it into cement, used for constructions.

Pardon my ignorance, though.

[bobfromhuddle]

We don't use CO2 to make cement, we use limestone, and CO2 is the byproduct of heating the limestone to make reactive calcium.

[henearkr]

Do you know ferrock?

It is a kind of cement that uses CO2 to cure.

[henearkr]

You can store CO2 and sell it to construction companies (to cure ferrock), to energy storage companies (who like to put the CO2 in huge bubbles nowadays, go figure), or to agricultural corporations (who enrich greenhouses air in CO2 to accelerate growth).

[adrianN]

You can heat definitely heat NaHCO3 to get CO2 and NaOH back. It just takes a lot of energy.

[DivingForGold]

"outperform" by only one metric too often fails usefulness. It's a one shot unless you heat the calcium carbonate to 900C, the compound in the article only requires 70C, and has quite a bit of ability to re-process CO2 absorption multiple times. Although solar ovens could reach over 900C, probably too dangerous for residential use.

[omgJustTest]

citation for the co2 scrubbers in home need?

[bilsbie]

Just to counter your extreme prediction, if co2 levels halve from here all life on earth goes extinct.

https://www.researchgate.net/post/Minimum_necessary_concentr...

[gspr]

Please stop trying to hurt every single human being with these derailments. There is no plausible mechanism by which carbondioxide levels would halve. That means you're just trying to derail the discussion by appealing to people's instincts about how fragile atmospheric composition is. Stop.

[bilsbie]

I can see how you’d think that. We’re all a product of the media we consume.

It’s an interesting exercise to try to figure out what the ideal co2 level should be. Why are we fixated on preindustrial levels. I’m very open to thinking 600ppm might be more ideal than the current level.

I feel that idea has some support from things like the optimal for many crops/greenhouse plants being 800–1,200 ppm. And that Earth's vegetation has greened since the 1980s due to increased CO2.

[loeg]

They aren't at risk of halving, though?

[belorn]

Comparing it to sofnolime (the more common used scrubber material for rebreathers), the cost sits around $10 per kg.

Cost will be the biggest question. A reusable scrubber need to be cheap enough that the reduce efficiency is worth it.

[29athrowaway]

Maybe we just need to make cyanobacteria that multiplies faster.