Covid-19: dogma over potential for prolonged droplet dispersal in air

Background / Outline: Many of us will have seen a plume of smoke drifting on the breeze from somebody smoking but it is much harder to show where the air breathed out, sneezed or coughed by another person has travelled in a street or aisle of a supermarket. Smoke can indicate where breath and tiny droplets coughed or sneezed may travel to but there are important differences to their dispersal due to the size of droplets compared to smoke particles. This perspectives article briefly explores evidence of dispersal of fine spray droplets in air, including not only microscopic droplets normally considered to form an aerosol and disperse in air, but also relatively large ‘ballistic droplets produced by coughing that might travel up to only a few metres, and then focuses on an under-reported intermediate-sized droplet that previous research investigating rain-splashed plant pathogens has shown can be blown significant distances in wind. The article gives examples of fall-speeds calculated for different sized droplets in still air and reports distances fine spray droplets were blown in a wind tunnel experiment. The article is very timely in that it discusses this issue in the context of the Covid-19 epidemic and the role of guidance on separation distances and use of facemasks to block a potential transmission route. This proposed ‘perspectives’ article is not only timely but also of importance to help ensure that good science is conducted to help researchers working on the current Covid-19 epidemic by making them aware of the wealth of existing knowledge produced by experts in other disciplines.