PM10 is the coarse fraction: particles up to 10 micrometers. The catch-all category includes pollen, dust-mite debris, pet dander, mold fragments, fibrous building dust, and the unburned residue of combustion. The body filters most of it in the nose and throat, which is why PM2.5 tends to dominate health-effect literature.
It still matters for two reasons. First, allergens travel here: ragweed pollen is around 20 µm, dust-mite debris around 10–40 µm. If you have hay fever or asthma, PM10 spikes are exactly what you feel before the symptoms. Second, the very upper end of PM10 is what you notice as "the room feels dusty". Visibility drops, surfaces accumulate, and ventilation systems clog.
The U.S. EPA NAAQS 24-hour PM10 standard is 150 µg/m³. WHO's 2021 24-hour guideline is 45 µg/m³. Indoor sources are mostly mechanical: vacuuming, bedmaking, dry sweeping, hobbies like sanding or sawing, and outdoor pollen drifting in through open windows.
Sensor design note: the Sensirion SEN66 reports four particle size bands (PM1.0, PM2.5, PM4.0, and PM10). When PM10 rises but PM2.5 stays flat, the spike is coarse (dust, pollen, dander). When both rise together, you are looking at combustion or smoke.
References
- EPA - National Ambient Air Quality Standards for PM www.epa.gov
- EPA - Particulate matter basics www.epa.gov
- AAAAI - Pollen allergy guide www.aaaai.org
- WHO Global Air Quality Guidelines (2021) www.who.int
