Prediction of Virus Survival Timescales in Surrogate Respiratory Sessile Droplets

The spreading of respiratory diseases through deposited saliva droplets is strongly dependent on the water evaporation process that may determine the virus viability due to the increase in concentration of nonvolatile compounds that are harmful for the virus. The drying time of a virus-laden droplet is influenced by environmental conditions, such as relative humidity and temperature, physical properties, such as the features of the surface on which it is deposited, and the wetting regime. Under this perspective, we addressed the modeling of an evaporating sessile droplet resting on a flat smooth surface, extending a previous diffusion-based model from the same authors. The evaporation behavior of sessile droplets of aqueous sodium chloride solutions and the virus viability of a surrogate virus (MS2) have been simulated considering different wetting regimes to account for different types of surfaces, ranging from highly hydrophilic to highly hydrophobic, as well as different ambient conditions, in terms of temperature and relative humidity. The results of calculations were given in terms of time evolution of contact angle, contact radius, mixture volume, and salt concentration, unveiling the importance of different wetting regimes for evaporation behavior and drying time. Longer evaporation times have been observed as temperature decreases and relative humidity increases. With reference to a surrogate virus, we evaluated the virus viability at different selected conditions, observing the classical U-shape of relative viability as a function of relative humidity of the environment at a certain temperature.