Definitions for "Aerodynamic diameter"
The diameter of a unit density sphere (density = 1 µg/cm3), which has the same settling velocity as the particle in question
Diameter of a spherical particle of unit density which has the same settling velocity in air as the particle in question. IPCS, 1987
Refers to the size of particles. It is the diameter of a sphere of unit density that behaves aerodynamically (has the same settling velocity in air) as the particle of the test substance. It is used to compare particles of different size, shape, and density, and to predict where in the respiratory tract such particles may be primarily deposited.