Smoke 101
Where smoke begins
From a spark in a forest to haze over a city hundreds of kilometres away.
Bilingual blurb by Samarth Yandhe
What Are Wildfires?
Wildfires are uncontrolled fires that can spread through forests, grasslands, and other areas with vegetation. Climate change can create hotter and drier conditions that increase wildfire risk in many regions. Wildfires also release large amounts of smoke and air pollution, which can travel long distances and affect communities far from the fire itself. (Gould et al., 2024; Rizzo & Rizzo, 2025)Climate, weather and risk
Heat, dry fuel, low humidity, wind and lightning all shape how wildfires start and spread. A warming climate can lengthen fire seasons and leave vegetation drier in many regions — but the risk in any one place still depends on local weather, land and fire management.
Smoke travels far
Rising heat lifts smoke high into the atmosphere, where winds can carry it across provinces and even countries. That is why communities with no fire nearby can still experience days of poor air quality.
Bilingual blurb by Samarth Yandhe
Wildfire Smoke
Wildfire smoke contains fine particles called PM2.5, along with gases and other pollutants. These particles can enter deep into the lungs and are associated with increased respiratory and cardiovascular health risks. Research shows that wildfire-specific particulate matter can have significant effects on human health. (Gould et al., 2024)Scale
How small is PM2.5?
PM2.5 means particles 2.5 micrometres in diameter or smaller. A human hair is commonly described as roughly 50–70 micrometres wide, so dozens of PM2.5 particles could fit across its width. Their tiny size is what lets them travel deep into the lungs.
Human hair ≈ 50–70 µm
PM2.5 ≤ 2.5 µm
Drawn approximately to scale. The dot on the right is the particle.
What's in smoke?
Smoke is a mixture of fine particles, gases such as carbon monoxide, and other pollutants, which vary depending on what is burning — trees, grass, or buildings and their contents.