Key facts
- PM2.5 is a subset of PM10.
- PM2.5 commonly comes from combustion and secondary atmospheric formation.
- The coarse PM10 fraction is often strongly influenced by dust and mechanical activity.
- Both readings matter; their relative levels can provide clues about dominant sources.
PM2.5 and PM10 compared
| Feature | PM2.5 | PM10 |
|---|---|---|
| Maximum aerodynamic diameter | 2.5 µm | 10 µm |
| Common description | Fine particulate matter | Inhalable particulate matter |
| Typical source emphasis | Combustion, smoke, secondary particles | Dust, mechanical activity, smoke and fine particles |
| Respiratory penetration | Can reach deep lung regions; some may enter the bloodstream | Can enter the respiratory system; larger fraction deposits higher in the airways |
| WHO annual guideline | 5 µg/m³ | 15 µg/m³ |
| WHO 24-hour guideline | 15 µg/m³ | 45 µg/m³ |
What the two readings can tell you
When PM2.5 accounts for much of PM10, combustion, smoke or secondary particle formation may be important. When PM10 rises much more sharply than PM2.5, coarse dust or mechanical activity may be contributing. This is a clue, not proof of one source.
Monitoring location, weather, source mix and instrument method all affect the relationship. Source attribution requires more evidence than a ratio alone.
Which is more important?
PM2.5 receives particular health attention because its smaller particles can penetrate deeply and remain suspended for longer. PM10 should not be ignored: elevated coarse particles can affect breathing, visibility and environmental conditions.
Frequently asked questions
Can PM2.5 be higher than PM10?
In a perfectly consistent measurement, PM2.5 should not exceed total PM10 because it is a subset. Short averaging periods, different instruments, locations or data-quality issues can produce apparent exceptions.
Which pollutant should I check first?
Check the overall AQI and its dominant pollutant, then inspect both PM2.5 and PM10 to understand the particle mixture.
Does a cloth mask filter PM2.5?
Ordinary cloth face coverings are not a dependable substitute for a certified, well-fitted particulate respirator.
Sources
This reference was prepared from the following primary public-health and regulatory sources:
- WHO Global Air Quality GuidelinesWorld Health Organization
- Particulate Matter (PM) BasicsUnited States Environmental Protection Agency
- Health and Environmental Effects of Particulate MatterUnited States Environmental Protection Agency