Wildfires guide
Wildfire Smoke and Air Quality: What the AQI Means and How to Protect Yourself
Wildfire smoke can travel thousands of kilometres and turn the air unhealthy in places nowhere near the flames. Here is how to read air-quality numbers and what you can do on smoky days.
Updated 4 November 2026
What is in wildfire smoke
Smoke is a mix of gases and tiny particles. The particles that matter most for health are called PM2.5: particles 2.5 micrometres across or smaller, about 30 times thinner than a human hair. They are small enough to get deep into the lungs and even into the bloodstream, which is why smoky air can make people cough, wheeze and feel unwell, and can make heart and lung conditions worse.
Smoke can travel very far. Smoke from wildfires in Canada has turned skies orange over New York and drifted across the Atlantic to Europe.
Reading the air quality index
Most countries turn pollution measurements into an air quality index (AQI): a single number or band that is easier to understand. Scales differ between countries, so always read the one your local service uses. The US AQI, used by many apps and websites, looks like this:
| US AQI | Level | What it means |
|---|---|---|
| 0–50 | Good | Air quality is satisfactory |
| 51–100 | Moderate | Acceptable; a few very sensitive people may be affected |
| 101–150 | Unhealthy for sensitive groups | Children, older people and people with heart or lung conditions should cut down on time outdoors |
| 151–200 | Unhealthy | Everyone may begin to feel effects; sensitive groups more seriously |
| 201–300 | Very unhealthy | Health alert: everyone is more likely to be affected |
| 301 and above | Hazardous | Emergency conditions for everyone |
Europe uses the European Air Quality Index, with six bands from Good to Extremely poor. Many forecasts also show the PM2.5 concentration directly, in micrograms per cubic metre (µg/m³). For comparison, the World Health Organization's guideline for a 24-hour average is 15 µg/m³; heavy smoke can push levels into the hundreds.
On smoky days
- Stay indoors with windows and doors closed when the air is unhealthy, and put off hard exercise outdoors.
- Clean the air in one room. A portable air purifier with a HEPA filter, sized for the room, removes most fine particles. Keep that room's door closed.
- Set air conditioning to recirculate at home and in the car, so it doesn't pull smoky air in from outside.
- Avoid adding indoor pollution: don't burn candles or incense, smoke, fry food or vacuum without a HEPA filter.
- If you must go out, a well-fitting FFP2, KN95 or N95 respirator filters fine particles. Cloth and surgical masks do little against smoke.
- Look out for others, especially children, older people, pregnant people and anyone with heart or lung conditions, who are most at risk.
- Follow your local health and air-quality advice, and get medical help for chest pain, severe shortness of breath or other serious symptoms.
Smoke forecasts
Smoke forecasts combine where fires are burning, how much smoke they give off, and the winds that carry it. They are useful for planning a day or two ahead, but smoke can shift quickly with the wind. The Fire app shows the air-quality forecast for your place next to the fires around it; see also How satellites spot wildfires.
Not an official warning service. In an emergency, follow your local authorities.