What is PM2.5, and why does it matter most?
PM2.5 is the fine dust that does the most harm in India's air: what it is, where it comes from, the safe limit (60 µg/m³) and how to breathe less of it.
What is PM2.5?
PM2.5 is particulate matter 2.5 micrometres across or smaller: tiny bits of dust, soot and droplets in the air. That’s about 30 times thinner than a human hair, too small to see.
Why it matters
Larger particles get caught in the nose and throat. PM2.5 is small enough to travel deep into the lungs, and the finest particles can pass into the blood. Long exposure is linked to heart and lung disease, which is why health agencies treat PM2.5 as the most important air pollutant to watch.
Where PM2.5 comes from in India
- Vehicle exhaust, especially diesel
- Burning crop residue, waste and wood
- Industry, brick kilns and coal power plants
- Cooking and heating with solid fuels
- Smoke from fireworks during festivals
In winter, cold still air near the ground traps pollution close to where people breathe. That’s why levels in north India often rise from October to January.
Safe PM2.5 limits
| Standard | 24-hour limit | Annual limit |
|---|---|---|
| India (CPCB, NAAQS) | 60 µg/m³ | 40 µg/m³ |
| World Health Organization (2021) | 15 µg/m³ | 5 µg/m³ |
On India’s AQI scale, PM2.5 up to 30 µg/m³ is Good and 31–60 is Satisfactory. Above 250 is Severe. See every level.
PM2.5 vs PM10
PM10 covers all particles up to 10 micrometres, so it includes PM2.5. Across India PM10 often reads high because of road and construction dust. Those coarser particles matter less for health than the fine ones.
So True AQI never ranks PM10 above PM2.5. When PM2.5 is over its limit, the app names it as the main pollutant.
The cigarette comparison
Researchers at Berkeley Earth estimate that breathing 22 µg/m³ of PM2.5 for a day is roughly like smoking one cigarette, in terms of health risk. It’s a rough guide, not a medical measure. True AQI shows this comparison only when the AQI is above 100, so it never makes a fine day sound scary.
What you can do on high PM2.5 days
- Check the live reading before heading out, not yesterday’s average.
- Move workouts indoors when the air is Poor or worse.
- Wear a well-fitted N95 outdoors on Poor, Very Poor and Severe days.
- Keep windows closed during spikes, and run an air purifier with a HEPA filter if you have one.
- If you have asthma or a heart or lung condition, follow your doctor’s advice on bad-air days.
This page is general information, not medical advice.
Questions people ask
What is a safe PM2.5 level in India?
India’s 24-hour standard for PM2.5 is 60 µg/m³ and the annual standard is 40 µg/m³. The World Health Organization’s 2021 guidelines are stricter: 15 µg/m³ over 24 hours and 5 µg/m³ a year.
Is PM2.5 worse than PM10?
PM2.5 is the bigger health concern because the particles are small enough to reach deep into the lungs. PM10 includes PM2.5 and is often high from dust in India, so True AQI names PM2.5 as the main pollutant whenever it is over its limit.
Do masks help against PM2.5?
A well-fitted N95 or equivalent respirator filters most PM2.5. Cloth and surgical masks filter much less.