I ordered our air400 Air Purifier just in time for the really bad air quality that descended on us due to all the fires in No CA triggered by the recent lightning storms. I have been so happy to have it and it really seems to do a good job. We have a separate air quality sensor that shows both PM 2.5 and the AQI (Air Quality Index) and while the readings on the sensor are typically 5-10 points higher for the PM 2.5 than the reading on the Bissel, directionally they track pretty well. It's such a relief to know that we can keep the air in our bedroom or living room fairly clean regardless of what's happening outside.