equivalent diameter

https://doi.org/10.1351/goldbook.E02191
The diameter of a spherical particle which will give identical geometric, optical, electrical or aerodynamic behaviour to that of the particle (non-spherical) being examined; sometimes referred to as the @S06027@ diameter for particles in non-turbulent flows.
Source:
PAC, 1990, 62, 2167. (Glossary of atmospheric chemistry terms (Recommendations 1990)) on page 2184 [Terms] [Paper]