The alveolar region of the lungs is endowed with several "cleansing" mechanisms whereby nongaseous substances of intrinsic and extrinsic origins are continuously removed. Collectively, the clearance mechanisms and pathways can be categorized into those effecting the removal of the readily transportable materials, eg, dissolved or monomeric substances, by passive and active absorption processes; and of the more persistent, less easily transportable materials, eg, "insoluble" dusts, by endocytosis and dissolution. The author critically assesses various clearance concepts and reviews the salient physiological and anatomical considerations that underly these concepts.
Morrow PE. Alveolar Clearance of Aerosols. Arch Intern Med. 1973;131(1):101-108. doi:10.1001/archinte.1973.00320070097011