The filtration efficiency of surgical masks for expiratory aerosol and droplets generated by vocal exercises

Transmission of an airborne disease can occur when an individual exhales respiratory particles that contain infectious pathogens. Surgical face masks are often used to reduce the amount of respiratory aerosol emitted into the environment by an individual while also lowering the concentration of particles the individual inhales. Respiratory aerosol generation is activity-dependent with high person-to-person variability. Moreover, mask fit differs among people. Here, we measure the efficacy of surgical masks (EN14683 Type IIR) in reducing both aerosol (0.3 – 20 μm diameter) and droplet (20 – 1000 μm diameter) emission during breathing, speaking and five speech and language therapy tasks performed by a human cohort. When participants wore a surgical face mask, measured particle number concentrations at the front of the mask were always lower than that for breathing without mitigation in place. For breathing and speaking, the through-mask filtration efficiencies were 80% and 87%, respectively, while for voice therapy tasks the through-mask filtration efficiencies ranged from 89% (“Hey!”) to 95% (/a::/). Size-dependent through-mask filtration efficiencies were high (80 – 95%) for particles 0.5 – 2 μm diameter, with masks filtering a greater fraction of larger particle sizes. For particle sizes >4 µm diameter, filtration efficiencies of surgical face masks for all tested respiratory tasks were ~100%. Surgical face masks significantly reduced the number of particles emitted from all respiratory activities. These results have implications for developing effective mitigations for diseases transmission through inhalation.