 Two alternative size-selective criteria, often used in atmospheric monitoring, are PM10 and PM2.5.PM10 is defined by ISO as "particles which pass through a size-selective inlet with a 50% efficiency cut-off at 10 μm aerodynamic diameter" and PM2.5 as "particles which pass through a size-selective inlet with a 50% efficiency cut-off at 2.5 μm aerodynamic diameter".PM10 corresponds to the “thoracic convention” as defined in ISO 7708