Airborne particles 25 microns or smaller can be inhaled. Those larger than 10 microns are normally deposited in the upper respiratory tract. Particles smaller than 10 microns can penetrate to the bronchi; particles smaller than 2.5 microns can penetrate to and lodge in the alveoli. These are responsible for most of the pathogenic effects, e.g., of pneumoconiosis.
Subjects: Public Health and Epidemiology.