As an aside: I had an interesting experience with my sensors the other day. I got a new package of Kirkland furnace filters and pm2.5 spiked to 100+. Was sneezing etc. Spent time diagnosing it, swapped out the sensor, eventually brought the outdoor one in to compare, and sure enough an old 3m one filtered it out within a six hours. Another new one spiked it. I ended up returning them with a comment but suspect customer service didn't care they might have a bad or mouldy batch.
