Mixture of small particles (solid, liquid or a mixed variety) and a carrier gas (usually air).

Note 1: Owing to their size, these particles (usually less than 100 µm and greater than 0.01 µm in diameter) have a comparatively small sedimentation velocity and hence exhibit some degree of stability in the earth's gravitational field.

Note 2: An aerosol may be characterised by its chemical composition, its radioactivity, the particle size distribution, the electrical charge and the optical properties.