Indoor-outdoor relationships for airborne particulate matter of outdoor origin

Abstract The air in a room was cleaned, and then airborne particulate matter was collected for various subsequent time intervals simultaneously in the room and outdoors nearby by pumping air through filters; the filters were analyzed by X-ray excitation for elements known to be primarily of outdoor origin (Fe, Zn, Pb, Br, Ca). Within several hours an equilibrium is reached in which the indoor/outdoor ratio is typically 0.3. A model is developed incorporating filtration in passing through walls, and deposition on, and resuspension from surfaces in the room. Experiments were carried out with windows “cracked” open and wide open, and with windows and/or other room surfaces covered with plastic sheet to determine the importance of various terms. Several rooms of various types and two automobiles were studied and it is concluded that a person remaining indoors with doors and windows closed probably inhales no more than 1 3 as much dust of outdoor origin as he would if he were outdoors.