Insights into spray impingement on mask surface: effect of mask properties on penetration and aerosolization of cough droplets

The emergence of the COVID 19 pandemic has demonstrated the importance of face masks, making them a part of the routine during the pandemic which is still continuing. The face masks act as source control, reducing the transmission of infectious respiratory droplets by acting as a physical barrier blocking the droplets during speaking, breathing, coughing, sneezing, etc. The novelty of current study is to replicate the droplet size distribution and velocity scale similar to an actual cough or a mild sneeze and conduct a fundamental study to investigate the effects of mask properties on model-cough impingement. The spray replicates the presence of both large-sized and small-sized droplets similar to an actual cough, which makes the observations relevant to real-life situations. The spray is impinged on different mask samples with varying properties like porosity, pore size, fabric thickness, and their combinations in multilayer configuration. The effect of mask properties on the droplet penetration volume is studied as it leads to the release of higher pathogen loading into the surroundings. A two step penetration criteria based on viscous dissipation and capillary effects have been applied along with a third criteria based on the porosity of the mask sample that is specifically applicable for the spray impingement. The droplets present in the impinging cough can penetrate through the mask, atomizing into the aerosolization range and thus increasing the infection potential. Hence the effect of mask properties on the droplet size distribution as well as the velocity distribution of the penetrated droplets has been investigated, which will be essential for estimating the range of infection spread. The filtration of virus-emulating nanoparticles as well as the fate of the penetrated respiratory droplets, with a susceptible person in the proximity, has also been investigated.