The size of a sphere of uniform density that has the aerodynamic properties of a specified particle. This particle size determines the period of time that a small body can remain suspended in the atmosphere. Depending on mass and air movement, prolonged atmospheric suspension is possible for particles ranging from 25 to 50 microns, but larger particles (200 microns or more) with low density can remain suspended in the atmosphere for many hours under suitable conditions. Particles smaller than 10 microns can be inhaled into the bronchi, and particles smaller than 2.5 microns, such as silica dust in mines, can penetrate to and lodge in alveoli.
Subjects: Public Health and Epidemiology.