PM10 vs PM2.5: The Difference, the Limits and What Removes Each

PM10 vs PM2.5 at a glance

From EPA's PM basics, the NAAQS table, the 2024 AQI rule and WHO's 2021 guidelines.

	PM2.5 (fine)	PM10 (inhalable)
Size	Generally 2.5 µm and smaller	Generally 10 µm and smaller (includes PM2.5)
Typical sources	Smoke, combustion, cooking, particles formed from gases in the air	Dust, construction, unpaved roads, fields, plus all PM2.5 sources
EPA annual standard	9.0 µg/m³ (primary)	None
EPA 24-hour standard	35 µg/m³	150 µg/m³
WHO 2021 annual guideline	5 µg/m³	15 µg/m³
WHO 2021 24-hour guideline	15 µg/m³	45 µg/m³
AQI Good band (24-hour)	0.0 to 9.0 µg/m³	0 to 54 µg/m³

Difference 1: size and where it goes

EPA compares both with a human hair, which is about 70 micrometers across, or about 30 times larger than the largest fine particle. EPA says some particles smaller than 10 micrometers can get deep into the lungs and some may get into the bloodstream, and it singles out PM2.5 as posing the greatest risk to health. Larger particles in the PM10 range are the ones you notice as visible dust on surfaces and as sneezing during pollen season.

Difference 2: the sources

EPA lists construction sites, unpaved roads, fields, smokestacks and fires as direct sources, and notes that most particles form in the air from reactions of chemicals such as sulfur dioxide and nitrogen oxides. Indoors, EPA names cooking, candles, fireplaces, unvented heaters, smoking and some hobbies. In practice:

• Mostly PM2.5: wildfire smoke, candle and incense smoke, searing and frying, tobacco smoke.
• More PM10: dusting, vacuuming, sweeping, pet dander, pollen drifting in through windows, sanding and other hobby dust.

Difference 3: the limits

EPA's limits treat the two differently because the health evidence differs. PM2.5 has both an annual health standard (9.0 µg/m³, lowered from 12.0 in 2024) and a 24-hour standard (35 µg/m³). PM10 has a 24-hour standard of 150 µg/m³ not to be exceeded more than once per year on average over three years. WHO's 2021 guidelines set lower values for both: 5 and 15 µg/m³ for PM2.5, 15 and 45 µg/m³ for PM10.

Difference 4: how the AQI treats them

EPA calculates a separate AQI for PM2.5 and for PM10, and the reported AQI is the pollutant with the highest index. That is why a dusty day can show a PM10-driven AQI even when PM2.5 is low.

EPA AQI breakpoints, 24-hour averages (40 CFR Part 58 Appendix G, 2024).

Category	PM2.5 (µg/m³)	PM10 (µg/m³)
Good	0.0 to 9.0	0 to 54
Moderate	9.1 to 35.4	55 to 154
Unhealthy for sensitive groups	35.5 to 55.4	155 to 254
Unhealthy	55.5 to 125.4	255 to 354
Very unhealthy	125.5 to 225.4	355 to 424
Hazardous	225.5 and up	425 and up

See our guide to the indoor AQI for how monitors turn these into a color.

Difference 5: what removes each

AHAM's air cleaner test reports three CADRs for three particle ranges: smoke (0.09 to 1 micrometers), dust (0.5 to 3) and pollen (5 to 11). The smoke CADR is the one that matters most for PM2.5, and the dust and pollen CADRs describe the coarser end of PM10. A HEPA-type filter captures all three sizes; the CADR tells you how much air the unit pushes through it. Our guide to CADR ratings explains the test.

Coarse particles also settle out of the air faster, so cleaning surfaces with a damp cloth and a vacuum with a sealed HEPA system matters more for PM10 than for PM2.5. For allergy-season pollen, see the best air purifiers for allergies.

Reading the two numbers together

Because PM10 contains PM2.5, the gap between the two readings tells you what kind of particle is in the room:

• Both high and close together: mostly fine particles, typical of smoke, candles or frying. Ventilate, use the range hood and run a purifier sized by its smoke CADR.
• PM10 high, PM2.5 low: mostly coarse particles, typical of dusting, vacuuming, pets or pollen. Run the purifier and clean surfaces; the reading usually falls faster because coarse particles settle.
• Both low but rising slowly through the day: outdoor air leaking in. Compare with the outdoor AQI from AirNow.

What about PM1?

Some monitors, such as the Atmotube PRO 2, also report PM1, particles 1 micrometer and smaller. EPA's national standards cover PM2.5 and PM10 only, so there is no EPA benchmark for a PM1 reading. Treat it as extra detail on the finest smoke particles, which are already counted in PM2.5.

Which one should your monitor show?

PM2.5 first. It is the number tied to EPA's annual health standard and the one that responds to smoke and cooking. Many consumer monitors also estimate PM10 from the same laser sensor. It is useful context for dust and pollen, but the independent accuracy figures we quote are for PM2.5, so treat a monitor's PM10 reading as a trend unless the maker or an independent test documents it. Our monitor accuracy guide explains how to read one.

Who should focus on which

• Watch PM2.5 if you live in a wildfire region, near busy roads, cook often with high heat, or burn candles or wood.
• Watch PM10 too if dust, pets, renovation or pollen are your main complaint.
• For both, size a HEPA-type purifier by its smoke CADR and keep up with cleaning. See the best air purifiers and PM2.5 explained.