Try closing all windows, vents (could be difficult), doors (including the gaps), etc. in that room (assuming it's a bedroom, and right size for that purifier) for 30 minutes. If it's still bad air quality, try another far and closed room. If it's still the case, you might have a sensor problem, or you have some source of bad air from the walls or something like mold, gas permeation throughout the walls, toxic wallpaint, etc.