Ok, so you compare your sensor to a reference sensor. But...
> If you compare two reference instruments, they should ideally measure exactly the same, namely the true pollutant concentration. But they don’t: A study from the US-EPA co-located two commonly used reference instruments (Met One BAM-1020 and Teledyne API T640) and found that, at certain concentration ranges, they diverged by over 25% from each other.
This reference instrument variability is especially true of the BAM, which due to its measurement technology has a high "noise floor" at low concentrations, while remaining a fairly good measurement at high concentrations. I believe two identical BAMs next to each other can easily have more than 25% disagreement at the lower end of the concentration range.
The T640 also recently had its approved calibration algorithm(s) updated, to a new set which often reads about 7% lower. What does that mean for T640 reference data collected in the past? I don't know, and AFAIK neither does the EPA really.
All that to say that reference instruments are still instruments with limitations, even if from a regulatory perspective we treat them as "truth".
> If you compare two reference instruments, they should ideally measure exactly the same, namely the true pollutant concentration. But they don’t: A study from the US-EPA co-located two commonly used reference instruments (Met One BAM-1020 and Teledyne API T640) and found that, at certain concentration ranges, they diverged by over 25% from each other.