Deposition of fractal-like soot aggregates in the human respiratory tract

Deposition of diesel exhaust particles in the human respiratory tract is calculated in terms of the equivalent mobility diameter while accounting for the aggregate's number of primary spherules. N-p, and its mass mobility fractal dimension. The size and shape of the soot particles studied correspond to emissions from diesel engines under different loading conditions. The aggregate's morphology, characterized by the aggregate mass mobility fractal dimension D-fm, is shown to significantly affect its age- and ventilation-specific deposition patterns in the human respiratory tract and hence, the exposure experienced by the receptor. Reporting respiratory tract deposition of diesel soot solely in terms of the aggregate mobility diameter, which lumps together size and shape, precludes a close look at deposition patterns of real particles and does not provide a complete picture for exposure inference. For sedentary adults, soot aggregates tend to deposit in the pulmonary region, with large open aggregates depositing to a greater extent than large compact aggregates. In most cases, and for open structured aggregates in particular, the aggregate deposition exceeds the deposition of their equivalent volume spheres. Whereas adults experience higher total respiratory tract soot deposition, infants are more susceptible to proximal deposition of open aggregates (D-fm < 2.2). For an adult performing intense activity both the tracheobronchial and the alveolar deposition fractions are smaller than at rest, whereas extrathoracic deposition increases during intense activity. Alveolar deposition of soot aggregates is evident mainly during rest and is more pronounced for small aggregates (N-p < 50). (C) 2011 Elsevier Ltd. All rights reserved.