PM stands for particulate matter, the tiny solid and liquid particles floating in the air. The numbers refer to particle size in micrometers: PM10 is particles up to 10 micrometers across, PM2.5 is the finer fraction at 2.5 micrometers or smaller, and PM1.0 is finer still at 1 micrometer or smaller. Smaller particles matter more for health, because they travel deeper into the lungs, and the finest can pass into the bloodstream. When your monitor shows three PM numbers, it’s telling you roughly how much of each size range is in the air around it right now.
What the numbers actually mean
The categories overlap by design. PM10 includes everything up to 10 micrometers, so it already contains the PM2.5 and PM1.0 particles. PM2.5 is a subset of PM10, and PM1.0 is a subset of PM2.5. For scale, EPA notes that PM10 particles are at least five times smaller than the width of a human hair, and PM2.5 is far smaller than that again.
| Reading | Particle size | Roughly what it captures |
|---|---|---|
| PM10 | Up to 10 micrometers | Coarse dust, pollen, mold spores, plus everything smaller |
| PM2.5 | 2.5 micrometers or smaller | Fine particles from cooking, smoke and combustion |
| PM1.0 | 1 micrometer or smaller | The very finest particles, which travel deepest |
Why smaller is worse
Size decides how far a particle gets into your body. Coarse PM10 particles are inhalable and can irritate the eyes, nose and throat. Fine PM2.5 particles reach deep into the lungs, and this is the fraction health research focuses on most. EPA links particulate matter exposure to decreased lung function and aggravated asthma, and long-term PM2.5 exposure is associated with more serious heart and lung effects. The finest particles are the reason a monitor breaks PM out by size instead of giving you a single dust number.
Where indoor particles come from
Some particulate matter drifts in from outside through doors, windows and gaps in the building, and a large share of outdoor PM can penetrate indoors. But a lot of it is generated inside your own home. According to EPA and California’s Air Resources Board, common indoor sources include:
- Cooking, especially frying, grilling, sautéing or anything that burns or chars food
- Smoking
- Burning candles or incense
- Wood-burning stoves and fireplaces
- Dust stirred up by everyday activity
- Particles that form indoors from reactions between gases released by cleaning products and air fresheners
Cooking is one of the biggest and most variable. How much PM you generate depends on the food, the method and the fat used, and burning food produces large amounts quickly.
What to do when your PM reading climbs
The most effective everyday step is ventilation at the source. EPA’s specific advice for cooking is to use a range hood whenever you cook, and to vent it outdoors if you can, which greatly reduces indoor PM exposure from cooking. Opening windows and running exhaust fans helps for other sources too.
Watching your monitor around everyday activities is genuinely useful here: check the kitchen before you cook, again while you cook, and once more after you’ve run the hood and opened a window. You’ll see the number rise and fall, which turns an invisible problem into something you can actually manage.
For particles specifically, filtration also works. A portable air cleaner with a true HEPA filter captures fine particles effectively, which is why HEPA is the standard recommendation for reducing indoor PM2.5.
How PM relates to formaldehyde and TVOC
It’s worth knowing that particulate matter and formaldehyde are different problems that need different responses. PM is solid and liquid particles, and a HEPA filter captures them. Formaldehyde and other VOCs are gases, so a standard HEPA filter does not remove them; ventilation and reducing the source do. A monitor that reads both, like the formaldehyde and particulate readings side by side, helps because it tells you which problem you actually have. If your formaldehyde is fine but PM spikes when you cook, that’s a ventilation-while-cooking issue, not a furniture issue.
Frequently asked questions
Is PM2.5 or PM10 more important indoors? PM2.5 gets the most attention in health research because these fine particles travel deep into the lungs, and cooking and combustion (common indoor sources) produce them. PM10 still matters, since it includes dust, pollen and mold spores that trigger allergies.
What raises PM2.5 indoors the most? Cooking is one of the largest and most variable indoor sources, especially frying, grilling and anything that burns food. Smoking, candles, incense and wood fires also raise it.
Does an air purifier lower PM readings? Yes. A portable air cleaner with a true HEPA filter is effective at capturing fine particles. Note that HEPA filters capture particles, not gases, so they don’t remove formaldehyde or other VOCs.
Why does my monitor show three different PM numbers? Because particles come in different sizes with different sources and health effects. Seeing PM1.0, PM2.5 and PM10 separately tells you more than a single combined dust reading would.
See your own particle levels
The FORMISENSE™ indoor air quality monitor shows PM1.0, PM2.5 and PM10 alongside formaldehyde, TVOC, temperature and humidity on one screen. Watch the numbers move while you cook, then after you ventilate, to see what actually lowers them. For the gases side, see our guide on what a safe formaldehyde level is.
Sources
- US EPA, Sources of Indoor Particulate Matter (PM)
- US EPA, Indoor Particulate Matter
- California Air Resources Board, Inhalable Particulate Matter and Health (PM2.5 and PM10)