Does anyone have any deeper insights into the workings of an Airgradient monitor?
I recently got the Airgradient outdoor monitor (model O-1PST). Shortly after installing and connecting it to HA, the larger PMs (1, 2.5 and 10) dropped to zero. All other measurements including PM0.3 showed values consistently.
Following a lengthy correspondance with the very responsive and friendly support at Argradient, I was sent a new sensor unit. I swapped the old sensor to the new one, and noticed a few things:
The current values in HA (on dasboard and queried via api) for the three larger PMs appear as zero almost constantly. However, the history charts showed curves - so there was definitely something recorded. To get some valid values I set up statistics entities to capture the max value of the past two hours. That worked - for a while.
The PM1 flatlined to zero soon after sensor replacement. PM2.5 and PM10 flatlined in HA at about the same time some 20 hours after the replacement. When checking the app.airgradient.com website it agreed on the flatlining of PM1 and PM10. However, there the PM2.5 is still producing values even as the HA graph is flatlined. Pardon my … WFT! 
I have calibrated the PMs via the app.ag site - once both on the old and the new sensors. No help.
There are a couple of public PM measuring points in (a more urban area of) the region where I live that I can use as comparison reference. The air is quite clean here but I don’t believe the absolutely unwavering zero values on my unit when the public points show a wide range during a day. Even before flatlining my unit maxed at about 4 when the public points hovered between 2 and 50 giving an average of 13.
One more thing … the CO2 value is constantly reported to be between 399 and 402 - day and night - regardless of wind conditions - in a foresty area. I find it a bit hard to believe that it would be so constant.
All ideas are welcome … or should I just return the product?