Abstract
Understanding how metal-oxide-enriched carbon aerosols deposit in the respiratory tract is essential for assessing their indoor health impacts, yet their inhalation behavior and age-dependent risks remain insufficiently quantified. In this study, we combined controlled chamber experiments, detailed particle characterization, and in silico dosimetry to quantify respiratory exposure to three representative metal-oxide-enriched carbon aerosols containing titanium dioxide (TiO₂), zinc oxide (ZnO), and copper oxide (CuO). The aerosols consisted of carbonaceous cores coated with oxidized metal species (Ti⁴⁺, Zn²⁺, Cu²⁺), designed to mimic aged soot typically encountered in indoor environments. Aerosols with diameters between 30 and 250 nm were generated in a 100-L mixing chamber, and their age-specific deposition was estimated using the Multiple-Path Particle Dosimetry (MPPD) model with ICRP morphometric parameters for 3- and 21-year-old subjects under light-activity breathing. Deposition profiles were similar between age groups up to the 15th airway generation but diverged in the deeper lung: adults showed higher deposition between generations 16 and 22, whereas children received greater deposition beyond generation 22. Despite a tenfold difference in exposure concentration between the two modeled episodes, the deposited mass per alveolus remained of similar magnitude, indicating that modest indoor concentrations can still result in appreciable alveolar doses. Modeled deposition patterns were consistent with previously reported experimental data in both magnitude and spatial distribution. Overall, children under seven years of age experienced approximately 35 % higher deep-lung deposition efficiency than adults, largely due to smaller airway dimensions and higher breathing rates. These results show that inhalation risk is governed jointly by particle physicochemical properties and age-specific respiratory physiology and underscore the need to incorporate both into future exposure and health-risk assessment frameworks for metal-oxide-enriched carbon aerosols in indoor environments.