Several viruses, especially respiratory viruses are effectively distributed by airborne droplets [147,148], and very obviously the human coronaviruses such as SARS-CoV [145,149,150], MERS [146,151,152], and SARS-CoV-2 [153,154,155,156] even though some controversy exists regarding respiratory transmission as the only means of distribution [157]. Some examples of viral air filtration are discussed next.