Role of pollen particle shape, breathing mode, and wind velocity on human aspiration and deposition efficiencies

Abstract

Understanding exposure patterns to seasonal pollen particles is crucial for public health. Multiscale fluid domains were established to conduct computational fluid–particle dynamics (CFPD) simulations, integrating semi-outdoor domain with human and airway models. Two reference wind velocities (0.25 and 0.40 m/s), breathing modes (steady inhalation and cyclic breathing), and particle shapes (spherical and ellipsoidal) with diameter range from 1.0 to 40.0 µm were examined to quantify the aspiration efficiency (AE) and deposition fraction (DF). The results demonstrate that with increasing wind velocity, AE decreased by approximately 15 %, particularly for large particle sizes, while the cyclic breathing profile increased AE by approximately 7 % compared with steady inhalation. Particle morphology was an insignificant determinant of AE, but exceptions were found at higher wind speeds, when 20 µm ellipsoidal pollen exhibited 13 % higher AE, and 5 µm exhibited 10 % lower AE compared to spherical pollen. Ellipsoidal particles with equivalent diameters of 5.0 and 7.5 µm exhibited slightly lower total DF compared to spherical particles. A detailed regional DF analysis revealed distinct deposition hotspots between spherical and ellipsoidal shapes. Ellipsoidal pollen (40 µm) accumulated intensely in the vestibule and posterior sections of the nasal cavity, whereas spherical pollen with diameters ranging from 5.0 to 10 µm showed slightly deeper deposition in the mid-airway generations. These findings emphasize that realistic breathing profiles, wind conditions, and particle morphology are key factors in pollen exposure assessments, suggesting the potential integration of microscales and mesoscales to quantify the dose and adverse effect of pollen particles in urban environments.