The AirVisual air quality monitor measures PM2.5 by constantly pulling air and particulates through its sensor chamber. A large particle, such as a piece of dust or similar, may enter the sensor chamber and get stuck during this process. This can result in a very high AQI number (e.g. AQI 1358) being displayed on devices.

To learn more about your air quality monitor and its PM2.5 readings, follow the links: