Short-range exposure to airborne virus transmission and current guidelines

Wang, J.; Alipour, M.; Soligo, G.; Roccon, A.; De Paoli, M.; Picano, F.; Soldati, A.

After the Spanish flu pandemic, it was apparent that airborne transmission was crucial to spreading virus contagion, and research responded by producing several fundamental works like the experiments of Duguid [J. Hyg. 44:6, 1946] and the model of Wells [Am. J. Hyg., 20:611-18,1934]. These seminal works have been pillars to past and current guidelines published by health organizations. However, in about one century, understanding of turbulent aerosol transport by jets and plumes has enormously progressed and it is now time to use this body of developed knowledge. In this work, we use detailed experiments and accurate computationally-intensive numerical simulations of droplet-laden turbulent puffs emitted during sneezes in a wide range of environmental conditions. We consider the same emission - number of drops, drop size distribution and initial velocity - and we change environmental parameters as temperature and humidity, and we observe strong variation in droplets evaporation or condensation in accordance with their local temperature and humidity microenvironment. We assume that 3% of the initial droplet volume is made of non-volatile matter. Our systematic analysis confirms that droplets lifetime is always about one order of magnitude larger compared to previous predictions, in some cases up to 200 times. Finally, we have been able to produce original virus exposure maps, which can be a useful instrument for health scientists and practitioners to calibrate new guidelines to prevent short-range airborne disease transmission.