Particulate sensors measure particulate matter (PM) in the air. This is done using the difference in how light scatters when encountering particles of different sizes.
Inside of the chamber, a laser emits a beam of light and the detector measures the light scattered by the particles in the air. Based on the amount of light scattered, the sensor can estimate the size of the particles that are present and produce a total count of particles within certain size classes. These size classes are typically 1 µm, 2.5 µm, and 10 µm, which is where the names PM1, PM2.5, and PM10 originate.