Sounds like it’s not working. There is always particulate matter to be detected, so even if you are fortunate enough to live in a low-pollution area, there should be some PM readings. The AQI is just an estimation of how healthy it is to breathe particulate matter per 8hours or ozone per 24 hours. So if the AQI is reported to be 90, it means you should definitely see some PM readings. My sensor was not very expensive but worked very well for a couple years until it broke a couple weeks ago, likely from moisture. Go to the guides section of the sensor community site and see which sensors they recommend. I think they’re largely interoperable.