Observations from carbon dioxide monitoring | Hacker News Reader

Observations from carbon dioxide monitoring

grieve-smith.com

67 pointscoloneltcb37 comments

The point about airplanes not running the ventilation on full throttle till takeoff has always driven me crazy. It's bad enough by itself, but it's also the time that lots of people are walking around. One sick person slowly making their way to the back of the plane while constantly waiting for people in front of them to put their luggage up will spread viruses throughout the entire plane, not just the folks within a few rows of them. This is the time when I most want the airplane to feel like wind tunnel. The economy looses billions every year to flu, cold and now COVID. If we can reduce that via ventilation (and maybe far-range UVC-C lights) in public spaces, we absolutely should. It's gonna pay for itself in no time. But it's a collective action problem where the costs are localized but the benefits help everyone.

> The point about airplanes not running the ventilation on full throttle till takeoff has always driven me crazy.

sucking in tarmac fumes would probably create more _immediate_ symptoms that could disrupt flights than waiting to ventilate after airborne, meaning your widely shared observation might reveal a business decision.

i.e., it might be just that tarmac fumes are really bad for everyone so they choose infectious coughed air over aromatic hydrocarbons from the tarmac.

I spent a few minutes looking into this and usually it's a mix of outside air and recycle air. However, the key point seems to be that, with the exception of the Dreamliner, the air comes form engine bleed, rather than a dedicated compressor. So that's the issue. Maybe I should just bring a little scuba tank

a collection of helium-air filled balloons might be more entertaining!

I've got an Aranet4 and started tracking CO2 and submitting it to IndoorCO2Map (via https://whn.global/indoor-co2-map-co2-monitoring-and-data-co...), but after a short period of time, there aren't really any surprises. Carrying a CO2 detector everywhere seems like mostly a way to give yourself anxiety.

If it's crowded now, or was recently, the CO2 is going to be high. If the building is old, or low volume, the effect will be worse.

Aren’t old buildings usually draftier? So less CO2

I've found old buildings to have generally worse air quality than newer buildings because of a lack of mechanical ventilation.

Nightingal, and Robertson before her, argued for better designs in hospitals to overcome these issues. We are over 150 years on from this arguement which has already been proven.

Using a digital sensor isn't required. The spread of various Corona viruses and others increase during colder weather and are more likely to spread in enclosed environments with limited air flow.

Cafe door shut, no air exchange in place, it's winter and half the clientele are reaching for hankies. Your probably catching a cold.

The article linked in the first paragraph is almost more interesting to me[1]. Some of these places, like the subway, have air frequently circulated that can filter aerosols but leave CO2; this limitation makes me somewhat doubt its usefulness as a proxy for disease transmission risk.

Apart from disease transmission, since I've gotten a CO2 monitor in my apartment I've noticed that running the gas stove or oven for even a little while will make a huge spike in CO2.

[1] https://grieve-smith.com/ftn/2026/02/so-you-want-to-monitor-...

Gas stove, oven, and clothes dryer with polyester/nylon will all cause my air quality sensor to go into the red.

Some takeaways:

- be very careful of what oils you're using when cooking food to ensure they are not turning volatile

- try to avoid using a dryer for non-natural poly clothes and use hang drying instead

Buying a (relatively expensive) CO2 monitor is one of those purchases that I was pensive about at first, but have zero regrets about a few years later. I was ignorant of a lot of things related to air quality, CO2 in particular. We were foolishly running a gas stove in a house with no ventilation, which probably had us up in the 1500+ range every time. This may seem like an obvious no-no to most of you but it was not a lesson we had ever learned.

You also get to see some other interesting observations, like how local construction digging up dirt on your street can cause elevated radon levels for months on end.

Can I ask what product you chose?

For in-house monitoring it's tricky because pretty much every vendor who makes more than bare-bones ones goes out of business or discontinues the product 12-18 months after you've bought it (Air Mentor, Awair, BlueAir, EdiGreen, Foobot, the list goes on). The best one I've found are QingPing, colour LCD touch-screen display with WiFi access, been around for years, regularly update the firmware and hardware, actually provide real product support, and have things like MQTT integration if you're using HA.

Airthings View Plus https://www.airthings.com/en/view-plus

I have a few of those around my house as well. However I have noticed that my VOC readings are not consistent, even if nothing in the area of the room has changed. I've reached out to their support about it but they're not much help. One thing I have noticed is a correlation with VOCs and C02, one(C02) seems to impact another(VOC)...which I don't think supposed to be the case. I was digging to the forums awhile back but the only conclusion I came up with is, you can't trust the VOC readings on these (or most consumer) devices...just too many variables and the sensors don't know/measure the full picture. It still bothers me though to look down in our son's room and see VOCs measurements elevated.

There was a moment where the VOC measurement was stuck at an elevated level. The solution was to blow some air in there to knock (presumably) dust off the sensor, which worked. It could be that the VOC sensor is not great, but it could also be that it gets dirty.

I constantly have two window air purifiers running at home. They lower the indoor CO2 and their filtration also dramatically lowers the indoor particulates. Granted, I can't run them as such in deep winter or deep summer.

Motivated by the article, I will proceed with using a continuous portable CO2 meter when not home.

If your air purifier sucks from and dumps into the same room it will do nothing for CO2 levels. Only for dust particulates.

I noted clearly that they're window air purifiers, suggesting that they intake from outside. As such they absolutely bring the indoor CO2 level closer to the outdoor CO2 level. This also happens to be a good way of capturing dust.

A CO2 sensor isn't going to tell you anything that your own common sense couldn't. Enclosed spaces with many people have higher levels of CO2.

Tracking CO2 levels seems like a pretty boring hobby.

I have a CO2 detector at home and bought some for family members, but I have never had a portable one so they stay at home. Some of the high CO2 ppm numbers in the article make me want to double check them. My vague understanding form reading the manual of the one I bought and watching how the numbers can be thrown off by cleaning products used near them make me wonder how much these high numbers are from sources other than CO2. That said I would still suspect that the a good chunk of the relative differences would be from CO2 changes.

And, if CO2 works as a proxy measurement for virus transfer, maybe misdetected CO2 also works as proxy measurement for virus transfer.

You may have a sensor that estimates CO2 based on measured total volatile organic components. These are called eCO2 sensors, and were used instead of the gold standard NDIR sensors due to cost.

There are better cheap sensors available now, like the one in the $30 IKEA Alpstuga: https://cleanair.community/t/thoughts-on-the-ikea-alpstuga-a...

Am I the only person here confused by the line the author draws between high CO2 levels and high transmissibility of viruses. I think they’re confusing correlation for causation here.

> In the first year of the COVID-19 pandemic I learned that we can estimate our level of risk by checking the concentration of carbon dioxide in the air, because when infected people breathe out virus aerosols, they also breathe out CO2.

The above is from the author early on. So they go out of their way to point out that it is an estimate and also point out the mechanism that allows it work as an estimate in some conditions. "when infected people breathe out virus aerosols, they also breathe out CO2."

The article does not reenforce this through out the article though and leaves it to the reader to keep in mind.

The previous post is essentially the background on this topic: https://grieve-smith.com/ftn/2026/02/so-you-want-to-monitor-...

> Why carbon dioxide? Because everyone who exhales COVID (or flu, or RSV) aerosols also exhales carbon dioxide, and good ventilation removes both disease aerosols and CO2. Under many conditions, the concentration of CO2 particles in a space can give us an idea of how much risk there is of catching or passing on a respiratory disease.

> Unfortunately, the relationship between the numbers on a carbon dioxide monitor and the disease risk is complicated, so there are some things to know if you want to do your own monitoring.

it’s a proxy but later work also showed high ppm increased the longevity of sars cov 2 in the air because the water droplets get more acidic due to carbonic acid

The problem isn't to breathe CO2, it's pumping it in the atmosphere... This article really misses the point.

The article has nothing to do with atmospheric CO2, it is about using CO2 as a proxy measurement for virus transfer.

Absolutely my bad, I overlooked the article and made this mean comment :')

Elevated CO2 levels reduces your cognitive abilities fairly significantly.

Absolutely my bad, I overlooked the article and made this mean comment :')

Very interesting article, but remember, making a room more airy will not mitigate the long term effects of CO2 on the Earth.

Older people may remember the push to make your house more energy efficient. So, seems you have a choice, higher energy bills or higher indoors C02.

So what is needed, move off fossil fuels. I remember seeing during the covid lockdown, C02 Levels did not raise for the first time in decades and I think they may have fell a little. That is because auto traffic decreased a lot. Right now I believe we are on our way to +2.5C :(

>So, seems you have a choice, higher energy bills or higher indoors C02.

An HRV or ERV can help with that.

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

The tension between an energy-efficient building and a well-ventilated one is real, but energy-recovery ventilation (ERV or HRV) is a thing and apparently works pretty well. Some kinds use counter-flow heat exchangers, some use an oscillating flow over a thermal mass (sometimes also a sorbent to keep moisture in or out).

Your reply is unrelated to the article which discusses measuring CO2 in order to gauge pathogen transmission risk.

   So, seems you have a choice, higher energy bills or higher indoors C02.

Or keeping a window open a fraction. Makes a huge difference in indoor air quality while not affecting room temperature or whatever else people are worried about much.

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