> Laser light is emitted from the sensor and focused by the sensor lens at approximately 5 mm from the top of the sensor’s lens surface.
> Particles traveling in free space due to the natural ambient airflow are detected when passing through the laser focal (sensitive) region.
> Due to the interaction between particles and light, the light scatters in different directions; a fraction is back-scattered towards the sensor, where the integrated photo-detectors detect it.
> The back-scattered signal is processed by unique algorithms (based on particle counts, particle relative velocity, probed air volume during measurement) to derive the particulate matter mass concentration.
You want to count particles per volume of air, so conventional sensors use a fan to have a constant volumetric flow and then count particles per second to infer particles per volume.
The way I interpret the above marketing language is that they use the optical sensor not only to count particles but also to measure the particle movement and infer airflow. So as long as there is some natural movement in the air, they can measure both particle count and volumetric flow, and thus infer particles per volume.