Filtering effect for small droplets (aerosols) by various masks; home-made of tea cloth, surgical mask (3M “Tie-on”) and a FFP2 (N95) respirator mask. The numbers are scaled to the reference of 100 (source of droplets) for illustrative purposes, calculated from the PF (protection factor) values in Table 2 of van der Sande et al, 2007. Measurement was performed with a Portacount counter that registers particles in the air with sizes in the range between 0.02 and 1 micrometer at the end of a 3-hour wearing period with no physical activity. The number for the protection are medians of 7 (or 8) adult volunteers per group. Protection at the beginning of the test was similar for the Tea Cloth and Surgical mask, but for FFP2 the protection was double. Children experienced substantially less protection (see van der Sande et al 2007) #Facemask #public #policy #filtering #particles #COVID19 #coronavirus #aerosolization #aerosols
