Size-specific filtration efficiency and pressure drop of school-aged children's woven and nonwoven masks at varying face velocities.

• Using a customized set-up employing an Electrical Low Pressure Impactor, the size-specific filtration efficiency, pressure drop, and filter quality of children's masks (surgical, KN95, 100% cotton, and partially-cotton-based masks) were tested at face velocities representative of adults and school-aged children. • As with adults' masks, children's nonwoven masks (such as surgical and KN95) showed a higher filtration efficiency and filter quality than woven masks. • In accordance with the single fiber theory, the lower face velocity for school-aged children yielded a higher filtration efficiency and lower pressure drop, but FE at particle sizes larger than 0.04 µm was low for woven masks. Differences in physiology and breathing patterns between children and adults lead to disparate responses to aerosols of varying sizes. No standardized method exists for measuring the filtration efficiency (FE) of children's masks to reflect such differences. Using an adult N95 mask as a control and two different face velocities (v f) (9.3 cm/s representing adults and 4.0 cm/s representing school-aged children), we tested the pressure drop (ΔP) through children's nonwoven masks (surgical and KN95) and children's woven masks (100% cotton and partially-cotton-based masks), as well as their size-specific FE between aerodynamic particle diameters of 0.02 and 2.01 μm. All three types of mask showed a 1 to 9% absolute increase in minimum FE at the lower v f and a significant decrease in ΔP. For children's surgical masks the increase in FE was significant for most of the examined particle sizes, but for children's woven masks the increase was limited to particles smaller than 0.04 μm. Lower v f for children is likely to lead to a higher FE, lower ΔP, and consequently higher filter qualities in children's masks. For woven masks, the FE for particles larger than 0.04 μm was low (typically <50%) for both v f 's studied. [ABSTRACT FROM AUTHOR]