Originally published at: Atmotube Pro 2 Review - Was It Worth the Wait?
If there’s one air quality monitor I’ve wanted over the past few years, it’s a device that measures both PM2.5 and CO₂ in a genuinely portable form factor. Up until now, I’ve usually carried two devices – something like an Aranet4 Home or AirSpot CO2 Monitor for carbon dioxide, and an Atmotube Pro (original) or AirBeam 3 for particulate matter. One for indoor use (CO₂), one primarily for outdoor use (PM). However, for some reason, finding a device that combines these two sensors in a portable package has proven surprisingly difficult. Sure, many indoor (and even some outdoor) monitors include both PM…
In the full review, I gave the disclaimer in the image below, mentioning that there look to be some issues with the automatic calibration of the STCC4 used in the Atmotube Pro 2. I’m unsure if this is an issue with the sensor itself, or just the Atmotube, but it looks to be improved but not totally removed.
Essentially, automatic calibration should allow the device to recalibrate its baseline approximately every week as long as it’s exposed to ambient air sometime during that period. However, when compared to a newly factory calibrated Aranet4 Home (and some other devices using the SCD41), I noticed that it has an odd behaviour where the readings would begin to deviate significantly and systematically.
While the device might provide very accurate readings (compared to the Aranet4) for a few days, it would suddenly jump 400ppm and read a consistent 400ppm higher for a couple of days. Then, seemingly randomly, it might systematically read 200ppm higher or even normally again. Since the trends are still correct, just offset, I assume this to be some kind of issue with the automatic baseline calibration. However, it’s odd that it occurs not on a 7-day cycle, but seemingly randomly.
When I first tested the device, these random jumps/changes happened multiple times per week and this made me hesitant to recommend the device because, unless the user also has a device to use as a reference, you would never know when the device is reading accurately or is offset.
Over the past few months, the readings look to be improving and I’ve only noticed this jump a couple of times in the past month. The graph below shows one example where the device read very similarly to the Aranet4 Home for around one week, before jumping to have a systematic 200ppm offset for 2-3 days, and then randomly correcting itself again. Please note that, during this time, the Aranet4 calibration was not adjusted.
I’m hoping that this issue can be completely removed in upcoming firmware updates because it will make the device a very solid combined portable air quality monitor. It’s good to see an improvement, but the issue does still exist - even if the device seems to read correctly 75% of the time now.