Term: Stokes number, \(St\)
https://doi.org/10.1351/goldbook.S06029

Definition:
Sometimes referred to as the inertial parameter; it is an index of the impactability of an aerosol particle. It is defined by the equation: St = 2 τ ( V t- v t ) D p where Dp is the diameter of a small drop, V t- v t is the difference in fall velocities of the drop and aerosol particles and τ is the characteristic relaxation time of a particle.

Related Terms:
1) aerosol (http://doi.org/10.1351/goldbook.A00176).
2) relaxation time (http://doi.org/10.1351/goldbook.R05287).

Source: PAC, 1990, 62, 2167. 'Glossary of atmospheric chemistry terms (Recommendations 1990)' on page 2216 (https://doi.org/10.1351/pac199062112167)

Citation: 'Stokes number, \(St\)' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.S06029

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