Face Masks Provide High Outward Protection Despite Peripheral Leaks: Insights from A Reduced-Order Model of Face Mask Aerodynamics

A face mask reduced-order model of aerodynamics and aerosol filtration is introduced. This model incorporates existing empirical data on filtration efficiency for different types of face masks, as well as the size distribution of aerosol particles during normal breathing. By considering realistic peripheral gap profiles, our model estimates both the peripheral leakage and the fitted filtration efficiency of face masks. Data from direct numerical simulations is also utilized in order to extend the current model to account for inhalation. Results of the model reveal that, for most types of face masks, a significant amount of respiratory airflow could leak through the mask periphery. However, most aerosols do not follow the flow path through the peripheral gaps but, instead, impact directly on the mask fabric. As a result, these face masks can filter out a large portion of the aerosol particles despite the significant peripheral leakage. The impact of mask usage on the transmission of respiratory viruses within communities is also explored by leveraging the insights gained from our model. By considering various scenarios, the potential reduction in viral spread through widespread mask adoption is assessed.