‘K’ Calibration Factor Of PurpleAir Flex?

[AirFright]

Hi Everyone
I am trying to find out the ‘K’ Calibration Factor of a PurpleAir Flex device so I can calibrate my Temtop M2000 to match the PurpleAir Flex’s readings and have both monitors outputting similar readings.
I read in the instruction manual (pictured below) the formula to calculate the ‘K’ Factor is K =PM2.5 (Target Value) / PM2.5 (Current Value) * K (Current Value).
Does anyone have any idea on how to work this out for a PurpleAir Flex?
I am after the ‘K’ Factor of the CF_ATM calibration, ALT_CF3 or ALT_CF3.4 conversion (Can you help with this @Lance?).

Please Note: This is not for research purposes. I am only wanting to do this so that my Temtop device is giving me similar readings to my PurpleAir Flex.

Thank You

[dwhitemv (Doug White)]

PurpleAir sensors are not appropriate to use as a reference sensor. There is too much interference from Plantower’s “adjustments”. If anything, you’d use the Temtop to create adjustment curves for the PurpleAir, as the responsiveness characteristics of the Temtop are (likely) published by the manufacturer and that can be used to create the K factor(s) to adjust it to a reference source (FRM/FEM or whatever is appropriate for your environment).

I’d recommend reviewing the papers posted in Lance’s thread, linked below, to understand the procedure.

Calibration of PurpleAir monitors

For the last few years, I’ve been analyzing the performance of the PurpleAir monitors. Last week the Sensors journal published my detailed comparison of the Plantower CF_1 algorithm with an alternative algorithm called ALT-CF3. This is Open Access. There is also a link within the pdf that takes you to the Supplemental Information (pictures of the PurpleAir and SidePak research-grade monitors, for example.) ALT-CF3 is a based on a method that has been used for decades to calculate PM2.5 from…

[AirFright]

Hi @dwhitemv
Apologies, I was not very clear as to why I was trying to find the ‘K’ factor. I am not doing this for research purposes, I am only trying to calibrate the Temtop so that it gives me similar readings to my PurpleAir Flex. I have edited my post to reflect this.
I use the Temtop in places where a PurpleAir device can’t and want it to be as close to the PurpleAir devices readings as possible.

I did look to see if Temtop had published anything on the ‘K’ factor but could only find what was in the instruction manual.

Unfortunately, I am unable to source a FRM/FEM monitor to use as a reference monitor when calibrating the Temtop.

[dwhitemv (Doug White)]

I’m trying to tell you that you will drive yourself insane trying to derive a linear correction factor to make the Temtop “match” the PurpleAir. The PA sensor’s responsiveness isn’t linear, it can’t be reduced to a simple K factor.

Years of research have gone into developing adjustment equations for PA sensors against FRM/FEM sources, and yet people still claim they’re wrong (by a factor of 2 even!)