Propagation in outdoor environments of aerosol droplets produced by breath and light cough

During respiration-based activities, possibly ejected microorganisms such as viruses pass from an infected subject to a target person through aerosol droplets. Research focused mostly on the mechanisms of aerosol generation, the droplet size, initial velocity, velocity and size distribution, the indoor aerosol propagation. We here consider the saliva aerosol associated with breath and light cough chosen since they are the standard and much common, gentle respiratory activities. We study the propagation in stagnant air of such aerosols from a point placed ahead of the mouth at a distance from it such that we can approximate the ejecta as a non-turbulent flux. We focus on different outdoor environments for selected weather conditions. We analyze the free fall of droplets (diameter, 5 µm to 200 µm), verifying whether they evaporate, or they impact on the ground, for different environment temperature, pressure, and relative humidity values. We provide a two-dimensional description of the evaporation path and of the dynamics of droplets (diameter, 5 µm to 100 µm) either moving within the air flux associated with the aerosol, or settling out of it and experiencing free fall through air. Calculated droplet propagation distances with the boundary conditions for the considered environments can be useful when discussing prevention measures to limit airborne transmission of pathogens.