  By now it is well-understood that the usage of facemasks provides protection
from transmission of viral loads through exhalation and inhalation of
respiratory droplets. Therefore, during the current Covid-19 pandemic the usage
of face masks is strongly recommended by health officials. Although three-layer
masks are generally advised for usage, many commonly available or homemade
masks contain only single and double layers. In this study, we show through
detailed physics based analyses and high speed imaging that high momentum cough
droplets on impingement on single- and double-layer masks can lead to
significant partial penetration and more importantly atomization into numerous
much smaller daughter droplets, thereby increasing the total population of the
aerosol, which can remain suspended for a longer time. The possibility of
secondary atomization of high momentum cough droplets due to impingement,
hydrodynamic focusing and extrusion through the microscale pores in the fibrous
network of the mask has not been explored before. However, this unique mode of
aerosol generation poses a finite risk of infection as shown in this work. We
also demonstrate that in single layer masks close to 70 % of a given droplet
volume is atomized and only 30 % is trapped within the fibers. The entrapped
volume is close to 90 % for double layer masks which still allows some
atomization into smaller droplets. We however found that a triple-layer
surgical mask permits negligible penetration and hence should be effective in
preventing disease transmission.
