Α dosimetry model of hygroscopic particle growth in the human respiratory tract

Abstract

The objective of the current study was to determine the growth and deposition of hygroscopic aerosol particles in the human respiratory tract. A hygroscopic particle growth methodology was incorporated into an existing particle dosimetry model (Exposure Dose Model 2, ExDoM2) using the κ-Kohler theory, the International Commission on Radiological Protection (ICRP) formulation for hygroscopic growth and mathematical formulations for taking into account the residence time, the influence of hygroscopicity on the particle’s density, and hygroscopic growth at 99.5% relative humidity. In order to validate ExDoM2, the results of the model were compared with experimental total deposition data for NaCl particles. The incorporation of the hygroscopic growth resulted in predictions closer to the experimental data than to model results without the use of a hygroscopic model formulation. The hygroscopicity plays a more significant role in the lower regions (tracheobronchial (TB) and alveolar-interstitial (AI) regions) of the respiratory tract. In particular, the hygroscopicity of NaCl particles decreases the deposition in the AI region for particles in the size range 0.03 μm ≤ aerodynamic diameter (dae) ≤ 0.2 μm while for the size range 0.3 μm ≤ dae ≤ 3 μm, the hygroscopicity increases the deposition in the AI region. In addition, it is observed that the deposition of (NH4)2SO4 and NH4NO3 particles with dae ≥ 0.30 μm is higher when the hygroscopic properties of the particles are taken into consideration. However, the particle deposition in the range 0.02 μm ≤ dae ≤ 0.25 μm is decreased due to hygroscopicity.