Smoke is a collection of tiny solid, liquid and gas particles. Although smoke can contain hundreds of different chemicals and fumes, visible smoke is mostly carbon (soot), tar, oils and ash. Smoke is a collection of these tiny unburned particles. Each particle is too small to see with your eyes, but when they come together, you see them as smoke.

Smoke from a forest fire is made up of: water, volatile organic compounds – a compound is volatile if it evaporates (becomes a gas) when it is heated, carbon, minerals in the tree’s cells, like calcium, potassium and magnesium (which are non-burnable and become ash).

When you put wood on a hot fire, the smoke you see is the volatile organic compounds (hydrocarbons) evaporating from the wood. They start to evaporate at about 149°C. If the fire is hot enough, the hydrocarbons will burst into flames. Once they burn, there is no smoke because the hydrocarbons are turned into water and carbon dioxide.