Aerosol deposition on face masks in an open environment during inhalation

Abstract

The aerodynamics of aerosols and their deposition on face masks play a critical role in determining the effectiveness of respiratory protection. While existing studies have focused on the risks associated with aerosol dispersion during exhalation, little attention has been paid to aerosol aerodynamics in an open environment, where aerosols can circumvent masks, during inhalation. This is because mask performance has primarily been evaluated by the particle filtration efficiency in closed pipe setups, which do not account for the aerodynamics of aerosols around the wearer's face. In this study, we conduct experiments in an open environment to investigate the aerosol flow around a face mask and the aerosol deposition under varying inhalation pressures. Our results indicate that an aerosol flow near a mask surface behaves like a viscous flow, stagnating within the range of human inhalation. Within this range, we find that the amount of aerosol deposited can be predicted by modifying existing aerodynamics theory. Using a theoretical model, a critical inhalation pressure is identified at which water aerosols begin to penetrate through a mask. Finally, we propose the aerosol circumvention efficiency as a new metric to assess mask performance in open environments by taking into account the effects of aerosol circumvention.