An aerosol is a collection of microscopic particles, solid or liquid,
suspended in a gas.
In the context of air pollution, an aerosol refers to fine particulate
matter, that is larger than a molecule,
but small enough to remain suspended in the
atmosphere for at least several hours.
The term aerosol is also commonly used for a pressurized container (aerosol
can) which is designed to release a fine spray of a material such as paint. It
has also come to be associated, erroneously, with the gas (propellant) used to
expel materials from an aerosol can.
Natural sources of aerosols include salt particles from sea spray, dust and
clay particles from the weathering of rocks. Aerosols can also originate as a
result of human activities and are often considered pollutants.
Aerosols play an important role in the
atmosphere namely in the condensation
of water droplets and ice crystals, various chemical cycles, and the absorption
of solar radiation.