When you open an air quality app, two numbers appear again and again: PM2.5 and PM10. They sound similar, but they describe very different particles — and understanding the difference can help you protect your lungs, your heart, and the people you care about.
What is particulate matter and where does it come from?
Particulate matter (PM) is a mixture of tiny solid particles and liquid droplets suspended in the air. The number after "PM" refers to particle diameter in microns (µm) — one millionth of a metre. Because these particles are so small, they stay airborne for long periods and travel deep into the body when inhaled.
PM comes from both natural and human-made sources. Dust storms, sea spray, pollen, and wildfires contribute naturally. Human activities — vehicle exhaust, power plants, industrial processes, construction, agriculture, and household cooking — are major drivers in cities worldwide.
Why regulators track PM closely
Unlike some pollutants that irritate only the airways, fine particles are linked to heart attacks, strokes, reduced lung function, and premature death. That is why PM2.5 and PM10 appear on every serious air quality dashboard, including Aether.
What is PM10?
PM10 refers to particles with a diameter of 10 micrometres or less — roughly one-seventh the width of a human hair. These are considered "coarse" particles.
Common PM10 sources
- Road dust kicked up by traffic
- Construction and demolition sites
- Agricultural tilling and harvesting
- Unpaved roads and mining operations
- Some industrial grinding and crushing processes
Health effects of PM10
PM10 tends to lodge in the upper airways — the nose, throat, and bronchi. It can worsen asthma, cause coughing and shortness of breath, and aggravate chronic bronchitis. While harmful, the body's natural defences (mucus and cilia) can trap and clear many of these larger particles before they reach the deepest parts of the lungs.
What is PM2.5?
PM2.5 particles are 2.5 micrometres or smaller — up to four times finer than PM10. These "fine" particles are the ones health experts worry about most.
Why PM2.5 is more dangerous than PM10
Because of their size, PM2.5 particles bypass the upper respiratory defences entirely. They penetrate deep into the alveoli — the tiny air sacs where oxygen enters the blood — and some ultrafine fractions can even cross into the bloodstream.
Once in the body, PM2.5 triggers inflammation, stresses the cardiovascular system, and is associated with increased hospital admissions for heart and lung disease. Long-term exposure is linked to reduced life expectancy, even at concentrations that may not look dramatic on a hazy day.
Common PM2.5 sources
- Diesel and petrol vehicle exhaust
- Coal and wood burning for heating and cooking
- Power generation and industrial combustion
- Wildfire smoke — increasingly significant globally
- Secondary formation from chemical reactions in the atmosphere
PM2.5 vs PM10: side-by-side comparison
Use this table as a quick reference when reading your local air quality report:
| Feature | PM10 | PM2.5 |
|---|---|---|
| Particle size | ≤ 10 µm (coarse) | ≤ 2.5 µm (fine) |
| Where it settles in the body | Upper airways (nose, throat, bronchi) | Deep lungs (alveoli); can enter bloodstream |
| Typical sources | Dust, construction, agriculture, road wear | Combustion, traffic, industry, wildfires, cooking |
| Visibility link | Often visible as dust or haze | Usually invisible; high levels create smog |
| Health concern level | Moderate to high | High to very high — primary driver of AQI |
| Body's natural defences | Can trap and clear many particles | Limited defence; deepest penetration |
| Long-term risk | Respiratory disease aggravation | Heart disease, stroke, lung cancer, reduced lifespan |
On most days, PM2.5 is the pollutant that drives your AQI reading — especially in urban areas with heavy traffic or winter heating.
WHO guidelines for safe PM2.5 and PM10 levels
The World Health Organization updated its air quality guidelines in 2021, reflecting growing evidence that even low levels of pollution harm health. Key 24-hour guideline values are:
- PM2.5: 15 µg/m³ (24-hour mean); annual mean guideline of 5 µg/m³
- PM10: 45 µg/m³ (24-hour mean); annual mean guideline of 15 µg/m³
Many cities — including major centres in South Africa, Europe, Asia, and the Americas — regularly exceed these thresholds. That is why personal awareness and real-time monitoring matter: official limits vary by country, but the health evidence points in the same direction.
Common sources of PM2.5 and PM10 pollution
Traffic
Vehicles emit PM2.5 directly from exhaust and generate PM10 from brake pad wear, tyre abrasion, and resuspended road dust. Living within 100 metres of a busy road significantly increases exposure.
Industry
Factories, smelters, cement plants, and power stations release both combustion particles and process dust. Industrial zones can create persistent hotspots on air quality maps.
Wildfires
Wildfire smoke is dominated by PM2.5 and can travel thousands of kilometres, turning skies orange and pushing AQI into hazardous ranges far from the fire itself.
Cooking
Indoor and outdoor cooking — especially over open flames or with solid fuels — produces fine particles that affect household members and contribute to neighbourhood pollution in dense urban areas.
How to protect yourself on high PM days
- Check levels before you go out: Use a live tracker to see current PM2.5 and PM10 readings and the forecast for the next few hours.
- Stay indoors when possible: Keep windows closed on high-PM days. If you have air conditioning, run it on recirculate.
- Use air purifiers: A HEPA-filter purifier can significantly reduce indoor PM2.5, especially in bedrooms.
- Wear a proper mask outdoors: Cloth masks offer little protection. N95, KN95, or FFP2 respirators filter fine particles effectively when fitted correctly.
- Time activities carefully: Pollution often peaks during morning and evening rush hours. Exercise early or postpone outdoor sport when PM is elevated.
Track PM2.5 and PM10 in real time with Aether
Aether shows live PM2.5 and PM10 readings alongside your city's AQI, hourly forecasts, and pollutant breakdown. Compare cities worldwide, spot trends over the day, and decide when it is safe to be outside — all from one free dashboard.
Check PM2.5 and PM10 levels for your city right now.
View live air quality on Aether