ABSTRACT
The term ‘aerosol’ refers to an assembly of liquid or solid particles suspended in a
gaseous medium long enough to enable observation or measurement. Aerosols may also
be described in other non-scientific terms, according to the source or appearance of the
particles. For example, liquid particles formed by condensation of supersaturated
vapours or by physical shearing of liquids, such as nebulisation, spraying, or bubbling
can commonly be termed ‘fogs’ or ‘mists’, whilst an aerosol consisting of solid and
liquid particles, created partly by the action of sunlight on atmospheric water vapour is
known as a ‘smog’. Another example is the solid or liquid aerosol resulting from incom-
plete combustion, which is termed ‘smoke’. Since aerosol particles range in diameter
from about 109 to about 104 m, the unit of micrometer (1 m 106 m) is generally
used when referring to the particle size of aerosols. For instance, a particle most haz-
ardous to the human respiratory tract is of the order of 106 m in diameter and this is
conveniently described as a 1-m particle. The term ‘micron’ is sometimes unofficially
used to refer to a micrometer.
