To describe the size of liquid or solid particles (
aerosol) the average or
equivalent diameter is used. For non-spherical particles collected in an impactor, for example, the aerodynamic
diameter of a particle of arbitrary shape and density refers to the size of a spherical
particle of unit density that would deposit on a given impactor surface.
Source:
PAC, 1990, 62, 2167
(Glossary of atmospheric chemistry terms (Recommendations 1990))
on page 2205