Aspiration efficiency and respiratory tract deposition of indoor suspended micro-particles during steady and transient breathings

The assessment of potential health risks from exposure to airborne contaminants and the inhalability of microparticles through human nasal breathing is crucial for the design of ventilation systems. In this study, using a standing computer-simulated person (CSP) directly linked to a numerical model of the respiratory tract, we investigated the aspiration efficiency (AE) of microparticles ranging between 1 and 80 μm under steady and transient breathing conditions. Two ventilation scenarios with displacement and mixed ventilation systems (DV and MV) were assumed for AE calculations. To determine the appropriate particle injection location, we investigated the position of highly inhaled particles corresponding to the breathing zone using a reverse particle-tracking simulation with reversed time progression. Additionally, the total and regional deposition fractions (TDF and RDF) of the inhaled microparticles on the respiratory wall surfaces were evaluated using the Lagrangian approach. The results indicate that the transient breathing cycle showed relatively higher AE and TDF rates compared to the assumed steady inhalation conditions, particularly for the size range 1–10 μm. An insignificant variation was observed in the AE and RDF results between different ventilation systems. However, microparticles in the MV room showed slightly higher AE than the DV system. Moreover, AE and penetration ratio were highly sensitive to the initially assumed particle density. For a comprehensive and accurate assessment of inhalation exposure to microparticles, we should predict the heterogeneous flow field formed around the human body and then analyze the AE and TDF in the respiratory tract during realistic transient breathing.