Simulation of the transition of respiratory droplets to aerosol states: Implications for pathogen spread

Airborne viruses constitute a real threat to the world and will continue to do so in the foreseeable future. Despite the intensive research in this field, the physical mechanisms of the droplet dynamics and aerosols carrying these viruses are far from being fully understood. Among the many variables that have critical impact on the dispersion of the virus carrying droplets and aerosols are the temperature and relative humidity, as these primarily determine the longevity of the liquid phase of the droplets. While previous research studied the dispersion of the virus carrying droplets and aerosols due to different physical and boundary conditions, we focus on the aerosols in the range below 10 μm as these have shown to be the most likely pathway for airborne transmission. In this study, the spatial and size evolution of droplets injected by the mouth through coughing are analyzed numerically and compared for different combinations of temperature and relative humidity. Of special interest would be tracking the aerosol droplets in part of an indoor location that serves as the volume that a conversation partner would draw breath from. We present quantitative data in dependence of temperature and relative humidity plotted against time assisting quantifying the possibility of transmission. An Eulerian–Lagrangian approach is used to study the multiphase flow consisting of a continuous fluid formed of air and water vapor and discrete droplets formed of liquid water. We present an analysis on the number of aerosolized droplets reaching a conversation partner depending on temperature and relative humidity. It was concluded that for aerosol transmission to a conversation partner, the humidity has the largest influence on the aerosolized droplets.