As demonstrated by the current COVID-19 pandemic, infectious respiratory diseases can place a heavy socio-economic burden on the most vulnerable members of our society. The disease overwhelms the health infrastructure worldwide3 , and its high infection rate and relatively long incubation period make it difficult to monitor and isolate infected persons. Current estimates indicate that approximately 35% of infected people have no obvious symptoms and can cause serious transmission of the disease without their knowledge. To curb the continued spread of the disease in the community, public health officials recommended several preventive measures, including social isolation and the use of masks in public places.

The reason masks or other face paints are recommended is to reduce the risk of cross infection by spreading respiratory droplets from an infected person to a healthy person. The pathogens that cause COVID-19 are primarily coughs, sneezes and even respiratory droplets from infected people when they talk and breathe. In addition to COVID-19, respiratory tract droplets are also the main route of transmission for other viral and bacterial diseases, such as the common cold, flu, tuberculosis, SARS (Severe Acute Respiratory Syndrome) and MERS (Middle Respiratory Syndrome) in the East, to name a few. These pathogens are encapsulated in respiratory droplets, which can fall onto healthy individuals and cause direct transmission, or spread onto inanimate objects. When healthy individuals come into contact with them, they can cause infection. In another method of transmission, if the droplets or their evaporated contents are small enough, they may be suspended in the air for a long time. Long after the infected person leaves the area, this can cause the air to spread and be inhaled by another person.

Respiratory droplets generated by healthy people and infected people through various activities have been studied in several studies. The transmission characteristics of these droplets can vary greatly depending on their diameter. Among the different studies in the literature, reported droplet diameters vary greatly, usually in the range of 1 µm-500 µm29 , with an average diameter of approximately 10 µm30 . It can be seen that the largest drop (diameter > 100 µm) follows the trajectory under the influence of gravity and drag. Medium sized drops can travel quite long distances in multiphase turbulent clouds. Smaller droplets and particles (diameters <5 µm-10 µm) can dominate.