An aerosol is a suspension of fine solid
particles or liquid droplets in air or another gas. Aerosols can be natural or
anthropogenic. Examples of natural aerosols are fog or mist, dust, forest
exudates, and geyser steam. Examples of anthropogenic aerosols are particulate
air pollutants and smoke. The liquid or solid particles have diameters typically
less than 1 μm; larger particles with a significant settling speed make the
mixture a suspension, but the distinction is not clear-cut. In general
conversation, aerosol usually refers to an aerosol spray that delivers a
consumer product from a can or similar container. Other technological
applications of aerosols include dispersal of pesticides, medical treatment of
respiratory illnesses, and combustion technology. Diseases can also spread by
means of small droplets in the breath, also called aerosols (or sometimes
bioaerosols).