Thoracic fraction, i.e., particle penetration through the extrathoracic region, P(ET)
, in adults and a 10 yr-old child. Data are daily averaged values for a median activity level, gradual augmenter breathing habit, and uncorrected for particle inhalability. Child-A and child-B are for a scaling factor of 1.0 and 1.26 in Equations 2 and 3, respectively. Horizontal red line highlights 50% penetration which occurs at 3.1 μm (adult female), 3.4 μm (adult male), 4.1 μm (child-B), and 5.1 μm (child-A).