According to Wikipedia Smoke is a colloid (a substance microscopically dispersed evenly throughout another substance) and comprises a collection of airborne solid and liquid particles and gases emitted when a material undergoes combustion, together with the quantity of air that is entraped or otherwise mixed into the mass.
Smoke particles are an aerosol (or mist) of solid particles and liquid droplets that are close to the ideal range of sizes for Mie scattering of visible light. This effect has been likened to three-dimensional textured privacy glass — a smoke cloud does not obstruct an image, but thoroughly scrambles it.
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