I recently got the air-purifier. For the last 2-3 weeks the AQI has been sitting at 001-004, last night out of nowhere it went up to around 180 AQI and was running at full blast. the only difference was that we had the window open most of the day, but even so, the air outside is not poor so that shouldn’t have registered so high either. Ideas, known issues?
Update - just turned it on this morning and its sitting steady at around 046AQI, so still high, but not that bad…
Any number of things could be related to it. Mine seems to go up when my heater is running.
The outdoor air may not be “polluted” in some ways, but there are so many other things…pollen, dust, etc. It also goes up for water particles in the air, so even steam from people showering, or humidifiers make it seem to go higher. It is totally based on the laser particle sensor on the back picking up ANY kind of particles in the air. Many of them we can’t see or smell, and some of them may not be “horrible” (like the humidifier putting water particles in the air). It is hard to say for any particular situation, all we know is that the laser particle sensor detected so many of some kind of particles in the air and was clearing it out so you weren’t acting as the filter for them instead. 
It’s springtime, so probably detecting pollen.