The Filtration Efficiency of Surgical Masks for Expiratory Aerosol and Droplets Generated by Vocal Exercises

Alicja Szczepanska, Joshua Harrison, Justice Archer, LAUREN MCCARTHY, Brian Saccente-Kennedy, Ruth Epstein, James Calder, Jonathan P. Reid, Bryan R. Bzdek, University of Bristol

     Abstract Number: 248
     Working Group: Aerosol Science of Infectious Diseases: What We Have Learned and Still Need to Know about Transmission, Prevention, and the One Health Concept

Abstract
The COVID-19 pandemic has increased interest in quantifying the effectiveness of different types of face coverings. Surgical face masks can help reduce the transmission of respiratory diseases, but there is still uncertainty about their efficacy to control emission of respiratory aerosols and droplets. This contribution presents measurements of respiratory aerosol and droplets generated during breathing, speaking and selection of voice therapy exercises both with and without surgical masks. A unique feature of this study is that the measurements were performed across a human cohort consisting of 15 healthy adults. The measurements were carried out in a laminar flow operating theatre, with a near-zero background aerosol concentration. Participants were instructed to perform a respiratory activity and aerosols or droplets were sampled both in front of and to the side of their face. Aerosols were sampled through a funnel into aerodynamic and optical particle sizers (APS and OPS), allowing quantification of the number concentrations, size distributions, and mass concentrations of 0.3-20 µm aerosols. Larger respiratory droplets (>20 µm) were quantified using a water‐sensitive paper approach. For all activities, surgical masks reduced the emission of aerosols and droplets. The filtration efficiency at mitigating the aerosols and droplets depended on the size of the particles as well as the type of activity performed. The overall aerosol filtration efficiency by number for a surgical mask measured in front of the participant was >90%. The droplet filtration efficiency was ~100%.