Though i believe you can turn off the auto calibration which is probably a good idea in busy city areas where I imagine outdoor CO2 is slightly higher than 400. And manually calibrate them with an actual known source.
Why measure CO2 outdoors?
We are able to detect emission sources pretty well now with our outdoor monitors [2] that have the SenseAir S8 NDIR sensor built in. You can see some real data in the blog post I wrote about launching our global CO2 map [3].
So setting up a dense network of these sensors in a city would allow to measure if for example the introduction of low-emission zones or switching to electric buses etc. would work.
Another use case is to check for leakage in underground CO2 storage facilities.
All-in-all it's still experimental (to some extent) but we know the accuracy is there and we can see more and more use cases as outlined in my blog post. So we now work hard to get more and more of these sensors out there to get more data to identify additional use cases.
[1] https://www.airgradient.com/blog/performance-of-low-cost-co2...
[2] https://www.airgradient.com/outdoor/
[3] https://www.airgradient.com/blog/airgradient-global-co2-map/
I.e. put sensor in vacuum chamber, remove all gases, then introduce know amount of gases to produce a known target environment.
Given their reference instruments, I assume they’re also capable of maintaining their calibration for a long period of known time, before they need to be re-calibrated. They would never rely on something as inaccurate as “20 mins outdoors” to calibrate themselves.
If the sensors are in an environment where the CO2 is always elevated, how do you keep it properly calibrated (eg if the CO2 never goes under 700ppm, how do you stop it from recalibrating so that it returns "400" when it should actually return "700") I know you can just turn calibration off but won't the sensors' accuracy decrease over time?
Only a plant cells containing chlorophyll and exposed to sunlight will photosynthesise. Notably at night there isn’t much sunlight, so normal respiration dominates a plants gas conversion processes, and results in them producing net CO2.
Based on the graphs in the blog post, I assume GP is placing the CO2 production on plants because it the CO2 levels peak at night, then return to normal every morning.
We need to get those rural voters more oxygen, STAT!
> Carbon dioxide is not released during photosynthesis, but small amounts of that gas are emitted both day and night as a by-product of cellular respiration. It is worth noting that the majority of plants absorb carbon dioxide during the day for photosynthesis and do so in greater amounts than they release for cellular respiration.
So depending on the time plants could easily be pushing out more CO2 than they are pulling it at that time, which could result in CO2 concentrations increasing during that time.
For example, to know that it's futile to try to turn on ventilation to lower the indoor CO2 concentration.
But on a hot windless summer day in a temperature inversion, my meter will read 700 or even 800 outdoors, as the CO2 from vehicles and maybe even power plants just sits around without going anywhere.
In the winter, if my indoor reading is 800 I open the window a crack to improve my concentration. On certain days in the summer, I just accept it's going to be 1,000 indoors and there's nothing I can do about it.