PM10 (coarse particulate matter)

AIR

3× federal 24-hour limit vs. California's

The federal 24-hour PM10 limit sits three times above California's, and the federal annual standard was dropped entirely in 2006. The coarse dust a PM2.5 sensor mostly misses is the part that flares airways on a high-wind dust day.

Settled science

Stasis Home Research Every claim on this page is graded against peer-reviewed health research and linked to its primary source.Updated July 2026

PM10 is airborne particulate matter 10 micrometers or smaller in diameter, small enough to inhale. It includes the fine PM2.5 fraction plus the coarse fraction PM2.5 leaves out: wind-driven soil and desert dust, sea salt, road and brake wear, and pollen. The coarse part deposits in the nose and upper airways, where it flares asthma, allergies, and sinus symptoms. HEPA captures it nearly completely on each pass.

PM10 (coarse particulate matter): what is it, and where does it come from?

PM10 is the mass of all airborne particles up to 10 micrometers in diameter, the fine PM2.5 fraction plus the coarse fraction between 2.5 and 10 micrometers that a PM2.5 reading does not capture. The coarse fraction comes from mechanical processes rather than combustion: wind-driven soil and desert dust, sea salt near the coast, road dust and brake and tire wear, construction, and biological particles such as pollen, mold spores, pet dander, and dust mite fragments. Each of those sources has its own trigger. Soil and desert dust rise in dry, gusty conditions. Sea salt is a steady baseline for homes within a few miles of any coast. Road dust and brake and tire wear track proximity to busy arterials. Construction registers within a block or so. Think of PM10 as the additive layer on top of PM2.5. These are extra sources in the same home, spiking at different times.

PM10 (coarse particulate matter): why does it matter?

PM10 matters mainly as an upper-airway irritant, because coarse particles are large enough to deposit in the nose, throat, and large bronchi rather than reaching the deep lung the way PM2.5 does. Short-term exposure is consistently tied to worse asthma, COPD flares, runny nose, cough, sinus flares, and more respiratory-related hospital and ER visits, especially in people who already have airway disease. The coarse fraction also carries microbial fragments that switch on the airway's innate immune response, a different mechanism from the deep-lung and bloodstream route PM2.5 takes. There is a measurable cardiovascular signal too, smaller than PM2.5's, seen in adults with asthma. The chronic-disease weight stays with PM2.5. PM10 is the fraction most likely to be why a sensitive household feels stuffy, scratchy, and worse on a windy day.

Coarse particles deposit in the nose, throat, and large bronchi rather than the deep lung, which is why PM10's strongest effects are upper-airway: worse asthma, sinus flares, and respiratory infections, separate from the deep-lung and bloodstream effects of PM2.5.Particulate matter air pollution: effects on the respiratory system (deposition-site distinction, coarse vs fine)
The coarse fraction on its own, independent of fine particles, measurably affected heart rate variability, blood lipids, and circulating immune cells in adults with asthma. It has its own effect.Coarse Particulate Matter (PM2.5-10) Affects Heart Rate Variability, Blood Lipids, and Circulating Eosinophils in Adults with Asthma, 2007
During an extreme Santa Ana wind event, dry desert winds eroded loose soil and drove PM10 across Southern California to daily concentrations far above the federal 24-hour limit, the coarse dust a PM2.5 sensor mostly misses.Dust pollution caused by an extreme Santa Ana wind event (Natural Hazards, 2022): Santa Ana winds eroded desert soil and drove PM10 far above the federal 24-hour limit across Southern California and the border region

PM10 (coarse particulate matter): what do we grade it against?

PM10 (coarse particulate matter) is held to two different numbers, and they do not agree. The health-based level for PM10, 24-hour (µg/m³) is as low as feasible (no level is known to be free of effect), from US EPA NAAQS table. The enforceable legal limit is 150. The table below lists every level on this page next to the source that set it.

Where the health research draws the line, versus the legal limit.
Contaminant	Health-based level	Legal limit	Source (health-based)
PM10, 24-hour (µg/m³)	as low as feasible no level is known to be free of effect	150 federal NAAQS, set 1987	US EPA NAAQS table
PM10, 24-hour, California (µg/m³)	as low as feasible state limit, 3x stricter than federal	50 California CAAQS	CARB, Inhalable Particulate Matter and Health
PM10, annual, California (µg/m³)	as low as feasible California keeps an annual limit the federal standard dropped in 2006	20 California CAAQS annual limit	CARB, Inhalable Particulate Matter and Health

Health-based levels come from peer-reviewed research and government risk scientists working without cost constraints, while legal limits are enforceable compromises. Your report grades to the health column.

What helps against PM10 (coarse particulate matter)?

3 approaches below reduce PM10 (coarse particulate matter) in a home, ordered from the most direct fix to the smallest change in habit. The most direct is Portable HEPA air purifier (room-sized, correctly sized CADR). Each entry also names what it cannot do, because no single fix covers every exposure route.

Direct fixes

Portable HEPA air purifier (room-sized, correctly sized CADR)
HEPA captures particles down to 0.3 micrometers at 99.97 percent, so for PM10 the capture is essentially complete on every pass. Run it continuously in the bedrooms and main living space, and keep it running through wind-dust and wildfire events.

Bigger retrofits

MERV-13 filter on the central HVAC system
Captures the coarse fraction at higher efficiency than the fine fraction, so the whole-home air handler does real PM10 removal every time it cycles. Confirm the blower can handle the filter's resistance before stepping up.

Free and behavioral

Closed-window protocol on forecast wind days, plus HEPA-equipped vacuuming
High-wind dust events usually come with one to two days of forecast notice (in Southern California these are the Santa Ana winds). Close windows, switch HVAC to recirculate, run HEPA, and defer yard work, the same playbook as a wildfire smoke day. Between events, vacuum with a HEPA-sealed machine rather than a standard one, which resuspends settled coarse dust instead of capturing it.
Behavioral steps reduce the indoor coarse-PM load, but they do not lower the outdoor concentration, and they do not address gas-phase pollutants, which need a different approach.

See how well each fix works

Method

HEPA air purifiers

Method

HVAC filters (MERV ratings)

PM10 is not the headline contaminant in your air. PM2.5 carries the chronic-disease weight, and our framing keeps it there. PM10 is the complementary layer: the coarse dust, sea salt, road wear, and pollen that a fine-particle sensor mostly misses and that spikes on a windy day. It is also the most controllable fraction, and the one most likely to explain why your airways feel worse during a high-wind dust event. HEPA captures it almost completely, MERV-13 catches it on every HVAC cycle, and closing the windows on a forecast wind day is free. You do not need to measure it to act on it well.

Common questions about PM10 (coarse particulate matter)

What is PM10?

PM10 is the mix of airborne particles 10 micrometers or smaller in diameter, small enough to inhale. It covers everything a PM2.5 sensor sees plus the larger coarse dust that sensor misses: wind-driven soil, sea salt, road and brake wear, and pollen. Because the coarse part is larger, it settles in the nose, throat, and upper airways and tends to show up as a stuffy nose, cough, or asthma flare rather than something felt deep in the chest.

What does PM10 stand for?

PM10 stands for particulate matter 10 micrometers or smaller in diameter. PM is particulate matter, the airborne mix of solid and liquid particles, and 10 is the size cutoff in micrometers (a micrometer is a thousandth of a millimeter). It is a mass measurement of every particle at or below that size, so it includes the fine PM2.5 fraction plus the coarse fraction between 2.5 and 10 micrometers.

How big is a PM10 particle?

A PM10 particle is 10 micrometers in diameter or smaller, by definition, and the label counts every particle at or under that size. Particles between 2.5 and 10 micrometers are the coarse fraction, mostly dust, sea salt, road wear, and pollen; anything 2.5 micrometers and under is the fine PM2.5 fraction. Both are far too small to see one at a time, but the coarse fraction is what shows up as visible dust settling on surfaces and vents after a windy or dusty stretch.

What is a safe or normal level of PM10?

There is no PM10 level known to be free of effect, so the health target is as low as feasible. For regulatory reference, the federal 24-hour limit is 150 micrograms per cubic meter, and California sets a stricter 24-hour limit of 50. Those are legal compliance limits, not health-based safety lines, and coarse-dust days can push outdoor readings well above them. Indoors, running HEPA continuously is what keeps your own level low.

What is the difference between PM10 and PM2.5?

The difference is particle size and where the particles land. PM2.5 is the fine fraction, particles up to 2.5 micrometers, which reaches the deep lung and bloodstream. PM10 includes PM2.5 plus the coarse fraction up to 10 micrometers, which is dust, sea salt, road wear, and pollen, and which deposits in the nose and upper airways and irritates them. PM10 is additive to PM2.5, not a substitute for it.

Why does the air feel worse on a high-wind dust day?

Dry, gusty wind erodes loose soil and carries coarse PM10 dust across a whole region, and severe events have measured well above the federal 24-hour limit. In Southern California these are the Santa Ana winds, where dry desert winds loft soil and carry dust across urban areas. That dust deposits in the nose, throat, and large airways, which is why it shows up as a stuffy nose, cough, sinus flare, or asthma symptoms rather than something you feel deep in the chest.

Will a HEPA purifier remove PM10?

Yes, a HEPA purifier removes PM10 very effectively. PM10 particles are larger than the 0.3 micrometer size HEPA captures at 99.97 percent, so almost none get through. Run a correctly sized unit continuously in the rooms where you spend the most time, and keep it on through wind-dust and wildfire events.

Does the home audit measure PM10?

The home audit does not measure PM10 directly. Its standard sensor measures PM2.5, and the audit is upfront about that gap. PM10 is captured through context instead: how close you are to busy roads or construction, recent wind-dust events, pets and flooring, and visible dust on surfaces and vents. The mitigation, HEPA and MERV-13 and the wind-day protocol, handles both fractions regardless.

Is coastal sea salt in my air something to worry about?

Coastal sea salt is largely benign for health, so it is worth knowing about for context rather than as something to fix. Homes within a few miles of the coast carry a steady sea salt contribution to their PM10. That contribution is part of why a coastal home can read a higher PM10 baseline than an inland one without that meaning more risk.