Respirable particles (PM4.0)
PM4.0 captures respirable dust up to four microns — the fraction that can still be drawn into the lungs, sitting between fine and coarse particles. It is useful for spotting dust from activity, materials and processes that finer or coarser metrics can miss.
The respirable middle of the dust spectrum.
PM4.0 fills the gap between fine and coarse particles, capturing process and activity dust that still reaches the lungs.
Respirable dust
Particles up to ~4 µm can be inhaled into the lower airways, where they aggravate asthma and allergic conditions.
Process & activity
Workshops, labs and busy spaces generate mid-size dust that PM4.0 tracks better than PM2.5 or PM10 alone.
Fuller picture
Measuring multiple size fractions reveals the particle-size mix, pointing to whether sources are combustion or mechanical.
Certification
WELL and RESET Air reward comprehensive particle monitoring across sizes; PM4.0 helps complete the picture.
Keep respirable dust in check.
PM4.0 has no standalone WHO limit, so it is read against practical healthy targets, similar to other respirable particle fractions.
Dust from activity and materials.
Mid-size particles are mostly mechanical in origin — generated by movement, handling and processes rather than combustion.
Work processes
Cutting, sanding, handling powders and similar tasks throw respirable dust into the air.
Materials & textiles
Fabrics, paper and packaging shed fibres and particles, especially during handling.
Foot traffic & cleaning
Movement and dry sweeping resuspend settled dust into the breathing zone.
Outdoor ingress
Coarser outdoor dust and pollen enter with ventilation and on clothing and footwear.