Aerosols

Also: Aerosol

A collection of airborne solid or liquid particles, with a typical size between 0.01 and 10 µm (micrometers) that reside in the atmosphere for at least several hours. Aerosols may be of either natural or anthropogenic origin. Aerosols may influence climate in several ways: directly through scattering and absorbing radiation, and indirectly by acting as cloud condensation nuclei or modifying the optical properties and lifetime of clouds (see Indirect aerosol effect).

Examples of Aerosols include dust, volcanic ash, pollen, soot, sulphates, even bacteria

Definition based on (revised from) IPCC AR4.