Most observations record PM10 and PM2.5 (This is particulate matter with a particulate size of 10 and 2.5 µm).
In general, for respiratory products dust is particle size above 5µm, fine dust is particle size between 5 and 2µm and very fine dust is smaller than 2µm. For disposable dust masks FFPP 1, 2, 3 should be used respectively.