Due to the function of the AirVisual air monitor's PM2.5 sensor, to constantly pull air and particulates through its sensor chamber, sometimes it is possible that a large particle, such as a piece of dust or similar, may enter the sensor chamber, and get stuck there. This can result in a very high AQI number (e.g. AQI 1358) being displayed.
Fortunately, this problem is straightforward to fix.
To dislodge the particle, you simply need a can of compressed air, with a small spray valve.
You could also use a hair dryer that can blow cold wind, but there's a risk damaging the sensor if not used properly. You can then direct the compressed air toward the PM2.5 sensor, and spray for a couple of seconds. You can access the PM2.5 sensor through the little gap in the middle hollow of the monitor, on the device's front side.
You should see your monitor's readings return to normal, once the particle is dislodged.
Call IQAir at 888-560-1020 if you continue to see abnormally high PM2.5 readings even after you've tried this solution so that we can further assist you and service your device if necessary.
See below image for reference: