Aerosols are involved in chemical processes in the atmosphere and play an important role in cloud and precipitation formation. They influence the Earth's radiation balance and thus also the climate, exerting an overall cooling effect.

There are aerosols of natural origin as well as those generated by human activity. Natural aerosols include sea salt, pollen, mineral dust and bacteria. Anthropogenic aerosols include soot particles and ammonium or sulfate particles. These arise due to combustion processes in industry and transport, or agricultural activity.