The measurements of human inhalability of ultralarge aerosols in calm air using mannikins

An idea was first introduced during the 1970s that particles cannot produce adverse health effect unless they are inhaled into the human respiratory tract. Since then several studies have been carried out to investigate the inhalable fraction of ambient aerosols. However, the previous studies were confined to the conditions of external convective flow and particle aerodynamic diameter smaller than 100 mu m. This paper reports the results from an inhalability study for particle aerodynamic diameter for a range of diameters which include diameters greater than 100 mu m under a condition of no external convective flow. The concept of mass balance was used in this study to derive an equation for determining the ambient particle concentration from which inhalability was calculated. The results suggested that difference in ventilation demands between adults and children does not affect inhalability, however, the inhaled dose was significantly higher in adults than children because of higher ventilation demand of adults. In terms of the breathing mode, the inhalabilities of oronasal breathing for people at heavy exercise are much higher than those of nasal breathing which simulates breath at rest and moderate exercise. The inhalability curve derived from this study indicated that a cutoff diameter for zero inhalability exists, which should be considered in the future revision of ACGIH inhalable aerosols criteria. (C) 1999 Elsevier Science Ltd. All rights reserved.