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Guide

How to Compare PM1, PM2.5 and PM10 Readings

A monitor that reports all three particle sizes is handing you a diagnosis. Smoke and cooking push PM1 close to PM2.5; dust and pollen open a gap to PM10. A few ratios turn three numbers into a source and a fix.

By the Akermin Editorial Team · 3 min read

Compare the three readings as ratios. PM1 is inside PM2.5, which is inside PM10, so the numbers must rise or stay equal in that order. When PM1 is close to PM2.5 (ratio above about 0.7) and PM10 is only slightly higher, the particles are fine combustion aerosol: smoke, candles, cooking flames, traffic. When PM10 is much higher than PM2.5 (ratio below about 0.5), coarse dust, pollen or resuspended dirt dominates. Act on PM2.5 for health; use the ratios to decide whether to stop a combustion source, run the hood, filter, or simply damp-dust and ventilate.

The nesting rule

PM10 ≥ PM2.5 ≥ PM1, always. The differences are the size fractions between: PM10 − PM2.5 is coarse (2.5 to 10 µm); PM2.5 − PM1 is the 1 to 2.5 µm band; PM1 is everything finer. See what PM1 is and PM2.5 vs PM10.

Two ratios

Ratio High value (near 1) Low value
PM1 ÷ PM2.5 Combustion: smoke, candles, gas flames, exhaust, secondary aerosol Larger fine particles: cooking oil droplets, some dust
PM2.5 ÷ PM10 Fine particles dominate; source is combustion or long-range pollution Coarse particles dominate: dust, pollen, cleaning, construction, sand

Signatures

Source PM1 PM2.5 PM10 Pattern
Wildfire or wood smoke High Slightly higher Slightly higher again All three close; PM1/PM2.5 above 0.8
Candle High Close Close Sharp rise on lighting and snuffing
Frying Moderate High Higher PM2.5 well above PM1; oil droplets span sizes
Vacuuming, dusting Low Moderate High PM10 far above PM2.5; settles within an hour
Pollen season, window open Low Low to moderate High Coarse spike when the window opens
Traffic beside a road High Close Moderately higher Fine with some road dust
Ultrasonic humidifier High Close Close Mineral aerosol; rises when the unit runs
High humidity, no source All rise together Hygroscopic growth; falls as RH drops

What consumer sensors actually do

Laser sensors count particles by scattered light in a few size bins and convert to mass with assumed densities. They see PM1 and PM2.5 reasonably and estimate PM10 from a small number of large-particle counts, so the PM10 figure is the least certain. Ratios are still informative because the errors are consistent within one device. See how to compare laser particle sensors and why particle sensors disagree.

Worked examples

  • PM1 38, PM2.5 42, PM10 46 at 9 p.m.: combustion; check for candles, a stove, or smoke coming in from outside. Close windows if outdoor is the source; run the purifier.
  • PM1 6, PM2.5 14, PM10 58 on Saturday morning: coarse dust; someone is cleaning. Damp-dust, HEPA vacuum, ventilate; it will settle within an hour.
  • PM1 20, PM2.5 90, PM10 130 at 6:30 p.m.: cooking oil aerosol. Hood on high, close the kitchen door.
  • All three double between 10 p.m. and 2 a.m. with RH rising to 80 percent: humidity growth rather than a new source; the dehumidifier or a cracked window will bring both down.

Acting on it

Health guidance is written for PM2.5; the 12 to 35 µg/m³ bands are the ones to act on. The other two numbers choose the action: filter and stop the source for fine particles, ventilate and clean for coarse. Monitors that report all three are noted in best air quality monitors.

IQAir AirVisual Air Quality Monitor Bundle, Swiss-Designed Indoor & Outdoor Sensors, Professional Grade Real-Time Air Quality Tracking

IQAir AirVisual Air Quality Monitor Bundle, Swiss-Designed Indoor & Outdoor

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Qingping Air Quality Monitor Gen 2, Air Quality Monitor Indoor Detects PM2.5, CO2, PM10, Noise, Temperature and Humidity, New Upgraded Alarm Clock Function, Air Quality Tester for Bedroom, Smart Home

Qingping Air Quality Monitor Gen 2, Air Quality Monitor Indoor

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Products shown because their documented specifications fit this guide. Price and availability are on Amazon and can change.

Frequently Asked Questions

Should PM10 always be higher than PM2.5?

Equal or higher, always, because PM10 includes PM2.5. If a monitor shows PM10 below PM2.5 it is a firmware rounding artifact or a fault.

What does a high PM2.5-to-PM10 ratio mean?

Fine particles dominate: combustion (smoke, candles, gas flames, traffic) or secondary aerosol. A low ratio means coarse dust, pollen or resuspended dirt.

Which number should trigger action?

PM2.5, against the 12 to 35 µg/m³ bands. Use PM1 and PM10 to decide what kind of action: ventilate for coarse dust, filter and stop the source for combustion.

Affiliate disclosure: Akermin earns a commission from qualifying Amazon purchases made through links on this page. Our editorial picks are based on documented specifications and owner feedback, not commissions.