Technically, an aerosol is a suspension of fine solid particles or liquid droplets in a gas. Examples are smoke, oceanic haze, air pollution, smog and CS gas. In general conversation, aerosol usually refers to an aerosol spray can or the output of such a can. The word aerosol derives from the fact that matter "floating" in air is a suspension (a mixture in which solid or liquid or combined solid-liquid particles are suspended in a fluid).
To differentiate suspensions from true solutions, the term sol evolved originally meant to cover dispersions of tiny (sub-microscopic) particles in a liquid. With studies of dispersions in air, the term aerosol evolved and now embraces both liquid droplets, solid particles, and combinations of these.
Some anthropogenic aerosols, particularly sulfate aerosols from fossil fuel combustion, exert a cooling influence on the climate which partly counteracts the warming induced by greenhouse gases such as carbon dioxide. This effect is accounted for in many climate models. Recent research, as yet unconfirmed, suggests that aerosol diffusion of light may have increased the carbon sink in the Earth's ecosystem.
Recent studies of the Sahel drought and major increases since 1967 in rainfall over the Northern Territory, Kimberley, Pilbara and around the Nullarbor Plain have led some scientists to conclude that the aerosol haze over South and East Asia has been steadily shifting tropical rainfall in both hemispheres southward. The latest studies of severe rainfall declines over southern Australia since 1997 have led climatologists there to consider the possibility that these Asian aerosols have shifted not only tropical but also midlatitude systems southward.
Oxides of nitrogen (NOx) in the atmosphere are a form of pollution which can give rise to smog and act as a greenhouse gas. Their persistence in the atmosphere is affected by aerosol droplets of water. In 1964 long chain fatty acids, either naturally produced from marine organisms dispersed into the atmosphere by wave action or man-made, were found to coat these droplets. In 2006 there was a study of the effect of the LCFA on the persistence of NOx, but the long term implications, although thought to be significant, have yet to be determined.