Because outdoor levels seem to vary significantly in a kind of 400-600 range, and it's impossible to calibrate a sensor outside without a reference point. On a windy winter day you can probably assume it's close to the global ~414, but on a muggy still summer day my sensors usually read significantly higher when holding them outdoors.
Our society deserves to have a publicly available map of outdoor emissions. There are lots of hard science and data analysis questions to solve in order to get there with reliable and cheap sensors, but I think it’s a journey worth going on.
We’re on discord and GitHub if anyone wants to come build with us.
I've been utterly baffled by how atmospheric CO2 is one of the very top issues of our time, and yet... I can get live temperature, humidity, and things like PM2.5, PM10, NO2, O3, etc... but not CO2.
Since you're in this area, do you have any insight as to why?
There are thousands of official air quality monitors used all over the world for calculating AQI and similar. Why did they skip CO2? Is there something inherently difficult or inaccurate about measuring it, is its short-term variation simply seen as irrelevant to health and not worth studying, or is there a political fear that live monitoring might somehow become ammunition for climate change deniers, along the lines of every winter blizzard leading to some people taunting "where's your global warming now?"
The US government measures CO2 at the Mauna Loa Observatory in Hawaii... and seemingly nowhere else?
As for your question about why does this not exist, there isn’t exactly one reason, but all of the reasons you stated above are certainly a part of the story.
The US government has not deployed a network like this primarily due to cost. Monitoring stations that the EPA install typically have a cost of at minimum $100k to install and finding people to maintain it is even harder.
Citizen science networks are generally started and deployed by for-profit companies. Because it’s hard to draw a direct line between a high CO2 measurement and some sort of immediate effect, most for-profit companies can’t justify the cost to build and sell something like this. For instance, purple—air is a for profit based on pollution particles. Consumers latch onto this because it has direct health effects and benefits you as the purchaser to know if you should open the windows or not today. Same with weather monitoring stations. There is a direct benefit for you in planning your day to know what the hyper local temperature outside is.
It’s a real shame and a place where capitalism fails society in my opinion. Having more data on the issue is important to inform gov. policy, hold emission sources accountable etc.
However I do think it’s worth doing, hence why the org. is a non-profit.
Another side of this issue is that CO2 is relatively difficult to measure reliably, because it is a very unreactive molecule. It is not susceptible to oxidation or most other reactions that can be used to determine its presence. Most reliable sensors use an IR light source and measure its attenuation by CO2.
An aquarium bubbler , or rather two, should be easy to plumb to a CO2 sensor. Just skip the water bath for one of them.
The calcium hydroxide is sold as "hydrated lime" and needs to just be stored isolated from CO2, and is mildly basic, so will slowly corrode your fingers (wash after touching, don't get any in your eyes).
Shouldn't even need gloves for this usecase, where one occasionally swaps the water and sediment for fresh stuff.
Btw, the waste, after soaking CO2, is just harmless limestone. Sprinkle around somewhat to make it a thin layer to ensure it all converts soon.
But realistically for home air quality measurements, it doesn't really matter. If you happened to calibrate it at 600 ppm you'd know when you later saw values below 400 ppm. Or you'd read a little high which probably isn't something you'd even notice.