Dosimetry simulations of ultrafine particles deposition to the human respiratory tract and transport to the olfactory region for female receptors

The regional deposited dose of ultrafine particles in the respiratory tract and their transport to the olfactory region was investigated through an existing particle dosimetry model (Exposure Dose Model 2, ExDoM2). The original dosimetry model was adapted to include a methodology that uses numerical modelling for the transport of ultrafine particles from the nose to the olfactory region. The mass dose to the oesophagus, blood, and lymph nodes was also calculated. Four different cases were studied: heating, traffic, nucleation events and background levels. The results showed that deposition in the olfactory region decreased with increasing particle size (from 0.40 % to 0.12 %). The majority of particles were estimated to penetrate into the thoracic region with 36 % of particles within the size range 14-33 nm deposited in the alveolar-interstitial region, followed by the tracheobronchial (21 %), the extrathoracic (11 %) and olfactory (<0.5 %) regions. In addition, a comparison between the mass, surface, and number doses indicated different governing sources such as a higher number dose was obtained during nucleation (10.5 x 10(8) particles), while higher mass (9.4 x 10(-2) mu g) and surface (7.1 x 10(12) nm(2)) dose was obtained during heating periods. Simulations also indicated that after clearance, 56.9 % of ultrafine particles were found in the alveolar region, a finding that is linked to their small size and low clearance rate of this region. Nevertheless, the dose per unit surface area and the dose per cell in the olfactory region were higher than in the alveolar-interstitial region.