Should…

Whenever I travel, I bring a CO2 meter with me. It’s amazing how often the air is bad. Often in unexpected places. My meter hit 3100 in an uber once. I didn’t even notice until I got to my hotel room and looked at the data log. It was a fresh, hot day outside. The uber had windows closed and AC on. I bet he had no idea - but he was driving with significant cognitive impairment. Takeoff and landing in planes are always the worst. If you get sleepy as the plane is taking off, it’s not you. The plane’s ventilation doesn’t work properly when the plane is stationary. So before a plane is in the air, they often hit 2500.

Building codes that address this are wonderful, however:

- Plenty of people live or work in older buildings, where are not up to standard. For example: my office probably violates the air quality sensibilities of the Victorian era, which is when it was originally built.

- Equipment breaks down, isn't operated properly, or wasn't installed correctly. Having monitors that measure air quality is an extra check. While you may not be able to get direct action upon a consumer sensor, it can help you push for action.

I've been in buildings of varying quality over the years. I've seen how it takes time to get people in to do air quality testing. Heck, I saw the government claim that the air quality was acceptable in schools during the pandemic because the schools had passive ventilation systems. That meant they could open windows. (To be fair, the air quality in most of those buildings was probably fine since that was how the buildings were designed. That said, such standards make it easy for some buildings to slip through the cracks.)

So yeah, sensors to the people!

I think modern domestic houses its the opposite. At least in Netherlands insulation is such a strong focus, due to climate change I think, that modern appartments have terrible ventilation

This is correct, but there's still a lot of opportunity to do better.

I've been involved with the build out of several office spaces in new and old buildings. We always took this sort of thing seriously and measured each room independently for a week (many at a time) ensuring we accounted for periods of high occupancy.

This let us tune the HVAC systems to operate more efficiently, ensuring comfortable temperatures and air circulation. Every time I've seen this done there were structural deficiencies that required remediation, some times it meant adjusting duct work.

Most modern office buildings are designed to be a platform for constructing spaces, as spaces usually evolve and change between leases and tenants. They're designed to accommodate this sort of thing.

However I've found that no build out nails this the first time. It's very hard! Often times things look fine but once you get people in the space things change drastically. It requires time and effort to address.

Several of my offices had such good air that I'd prefer being there over pretty much anywhere else -- even outside on poor AQI days.

I've also found that a lot of offices don't do any of this and their air quality is noticeably poor. And lastly I've found that the oldest buildings, including schools -- and I'm talking really old -- have very good air because they are so incredibly leaky. They're usually harder to cool and heat, though.

Sensiron STCC4 uses thermal conductivity sensing thats very compact (4x4x1.2mm). It's pretty new to the market, but maybe in the future it'll happen.

Oxygen sensors used in car catalyst systems use a different effect based on electrochemistry. I see no reason that couldn't be minuaritized to grain-of-sand size.

The question is if oxygen levels are as good an indicator as CO2 levels... I suspect not.

Mesh with the other Apple/et al devices in the room to take multiple samples and aggregate the results for an overall picture of the ambient co2

I would hesitate to say the IKEA is worse. Inside the IKEA is a reputable Sensirion all in one sensor module. It's much cheaper and smaller because the CO2 sensor in it is using different (newer) technology that only released a few years ago from Sensirion.

(Upd: the IKEA does have lower accuracy, with ±100 ppm instead of ±30 ppm. From the SEN63C datasheet)

I got the ikea sensor, I’d say it’s way more accurate than you need for personal use. I wouldn’t use it as a scientific instrument but it’s well good enough to see if the room is ventilated enough.

I was shocked to see just how fast CO2 climbs while in a room, and how just opening the window just a crack was enough to restore the room to baseline co2.

The thing runs on usb 5v so the power consumption is negligible. It also plugs in to home assistant great.

Ruuvi Air[1] seems to be close to the middle in both price and CO2 measurement accuracy between aranet4 and the IKEA device. I don't have personal experience with Ruuvi Air specifically, but have been using their cheaper Ruuvi Tags (that don't measure CO2) for temperature, humidity and air pressure measurement at home and office.

[1] https://ruuvi.com/air/

> I also don’t know how much electricity they pull.

It can't be much, since the Aranet 4 can run for years on 2 AA batteries.

From what I learned from Apollo 13, even with O2 in the air, CO2 can still be poisonous.

I don’t think that’s right. If people have an easy way to measure the levels, and they can see something on their phone like ‘you spent 8 hours today above 2000ppm CO2’ then the room will care a lot more than it did before, and people will be able to quickly see whether they have improved things. At my employer, I think it took us around 1000 employees until we randomly hired someone who happened to care a lot about CO2 levels and I think they managed to cause a decent increase in the amount that the company cared / thought about levels (this was around the end of Covid though so part of this may have been due to using CO2 levels as an indication of insufficient ventilation/air filtration).

Depending on the state, newer buildings do have regulations on air ventilation and quality.

The rooms being discussed here are mostly ones which would have been built before this was taken more seriously. Classrooms, older office buildings, etc.

NYC is full of buildings which would never pass any code today but are still happily occupied. It’s a trade off, I think.

Can't you just open a window a bit?

I can just imagine the horrors and skin crawls that your last sentence has evoked in some people's minds. Not the state!!

But seriously, so much care needs to be taken here. OK, well "care" at least. Employers certainly would benefit from scrubbing CO2 from the air, in terms of productivity. I'm willing to bet that with central air it would be quite easy, and even with heat and AC off, lots of places still circulate the air regardless.

So the central place to scrub is already there.

But then you have other issues. Such as, will your body adapt to 8 hrs of reduced CO2, and then you become torpid and barely awake when not at work. Such a horrid thought, that is to me. And what if employers learn that the tiniest boost of O2 helps too! Now your body becomes accustomed to that, and what are the long term effects there?

I can personally envision myself being concerned. I guess the legislation could be crafted to "the same CO2 levels found just outside of downtown city core" or some such blather. Maybe even same for O2. So that you're at least pegged to something normal for the area.

Maybe that's where the state could come into play. A simple, highly accurate monitoring station which has an API to be polled.

Come to think of it, CO2 and O2 rates fluctuate during the 24 hour cycle. Trees need O2 to live, but only produce O2 during the day. And so differing amounts of light might mean up and downs in these numbers. It may be another circadian rhythm. Getting it the same as in a nearby forest, might be the healthiest thing of all.

Those $15 ones are also straight up scams. They just estimate (lie) for the readings based on other sensors.

And I believe the accuracy is also not great on these cheap ones. The product in the OP's photo costs $200 where I live! And ISTR finding the sensor itself contributes a lot to this cost.

IIUC they also need fans. The one I have in my home has one that's actually integrated into the sensor unit.

For the purposes of indoor ventilation monitoring you can calibrate by occasionally exposing the sensor to fresh air. Either taking it outside or just the room not having people in it. The sensor will treat the lowest reading it gets as 400ppm since this is what outdoor air is.

A sensor mounted in the office will get calibrated every night when the office is empty.

Not really. For ventilation purposes, a good sensor remain within 10% variation for nearly ten years. We are not running a controlled science experiment here.

I don't think that's true at all. Capnography, the measure of carbon dioxide partial pressure is wholly separate from pulseox:

> Pulse oximeters have some limitations. They can only employ light at two wavelengths. Thus the devices can only distinguish between hemoglobin and oxygenated hemoglobin. When carboxyhemoglobin and methemoglobin are also present, there are two additional wavelengths required for differentiation. In the presence of elevated carboxyhemoglobin levels, pulse oximetry overestimates the true saturation of oxygen as carboxyhemoglobin binds with a higher affinity than oxygen. In the case of carbon monoxide poisoning, the absorbance spectrum of carbon monoxide is very similar to hemoglobin, which results in a falsely high level of oxygen (overestimation of oxygen saturation) ...

https://www.ncbi.nlm.nih.gov/books/NBK539754/

I don't think that's safe to assume at all, for two reasons:

1. CO2 has effects on the human body of its own that aren't simply a lack of oxygen, and vice-versa. [0]

2. The baseline proportions involved aren't close, so even doubling CO2 isn't going to show up easily as a large swing in in oxygen%.

For example, the article references a study where the CO2 proportion going from 0.04% -to 0.25% correlates to mental problems.

Even if the watch could sample atmosphere directly, is it sensitive enough to detect a shift from 21.00% -> 20.79% oxygen?

As it's estimating oxygen in the owner's blood, it might not detect anything different at all... not if the owner's body has already compensated by breathing harder or by "underclocking" their brain to make dumber decisions.

[0] https://en.wikipedia.org/wiki/Asphyxiant_gas