PM10 (coarse particulate matter)

AIR

3xfederal 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 ResearchEvery claim on this page is graded against peer-reviewed health research and linked to its primary source.Updated 2026-06

PM10 is airborne particles up to 10 micrometers wide, the coarse fraction that PM2.5 leaves out. It is wind-driven soil and desert dust, coastal sea salt, road and brake wear, and pollen. It deposits in the nose and upper airways and flares asthma, allergies, and sinuses. HEPA filtration captures it at essentially 100 percent per pass, and on forecast wind days, closing windows is the lever.

What it is, and where it comes from

PM10 is the mass of all airborne particles with a diameter up to 10 micrometers. It includes the fine PM2.5 fraction plus the coarse fraction between 2.5 and 10 micrometers, which is the part a PM2.5 reading does not capture. The coarse fraction comes from mechanical processes rather than combustion. The main sources are wind-driven soil and desert dust in dry, gusty conditions, sea salt aerosol for homes within a few miles of any coast, road dust and brake and tire wear near busy arterials, construction within a block or so, and biological particles such as pollen, mold spores, pet dander, and dust mite fragments. Think of PM10 as the additive layer on top of PM2.5: same home, same envelope, a different set of sources that spike at different times.

Why it matters

PM10 acts where it lands. Because coarse particles are larger, they deposit in the nose, throat, and large bronchi rather than reaching the deep lung the way PM2.5 does. That makes PM10 an upper-airway irritant. 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, showing the effect is real even though it is smaller than the PM2.5 cardiovascular signal.Coarse Particulate Matter (PM2.5-10) Affects Heart Rate Variability, Blood Lipids, and Circulating Eosinophils in Adults with Asthma, 2007
Santa Ana winds drive sharp PM spikes across Southern California, as dry offshore wind erodes desert soil and carries the dust across the basin.Santa Ana Winds of Southern California Impact PM2.5 With and Without Smoke From Wildfires

What we grade it against

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 feasibleno level is known to be free of effect	150federal NAAQS, set 1987	US EPA NAAQS table
PM10, 24-hour, California (µg/m³)	as low as feasiblestate limit, 3x stricter than federal	50California CAAQS	CARB, Inhalable Particulate Matter and Health
PM10, annual, California (µg/m³)	as low as feasibleCalifornia keeps an annual limit	20federal annual PM10 standard revoked in 2006	CARB, Inhalable Particulate Matter and Health

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

What helps

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.

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 the fraction most likely to explain why a sensitive household feels worse during a high-wind dust event, and it is also the most controllable. 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

What is the difference between PM10 and PM2.5?

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. The coarse part 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 dust across a region, and severe events have measured well above the federal 24-hour limit. In Southern California these are the Santa Ana winds, where dry offshore wind drives desert dust across the basin. 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, very effectively. HEPA filters capture particles down to 0.3 micrometers at 99.97 percent, and PM10 particles are larger, so capture is essentially complete on each pass. 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 standard sensor measures PM2.5, not PM10, 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?

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