theoretical prediction of the size and lifetime of evaporating sneeze droplets in a confined space: a guideline to control of covid-19 virus transmission

The size and lifetime of evaporating sneeze droplets in the indoor environment were studied experimentally and theoretically. the effects of indoor temperature t∞ and indoor humidity rh∞ on evaporating droplets with the initial diameters of 4.9, 8.1, 17.2, and 29.7 μm were investigated. the size distribution and mean size of droplets were obtained by a laser particle sizer. the experimental data showed that the possibility of aerosolized droplets increased from 25.5 to 36.1 % by increasing t∞ from 18 to 30 °c and decreased from 36.1 to 13.6 % by increasing rh∞ from 30 to 60 %. a one-dimensional droplet evaporation model was used to estimate the lifetime of the droplet. a critical rh∞ of 40 % was found; above it, the lifetime of the droplet exponentially increases. the effect of the initial diameter of droplets was higher than that of rh∞ and also the impact of rh∞ was higher than that of t∞ on the lifetime of the aerosolized droplet nuclei. a significant effect of environmental conditions on the lifetime of the droplet was found over the range of 26 °c ≤ t∞ ≤ 30 °c and rh∞ ≤ 40 %, while the effect decreased in the range of 18 °c ≤ t∞ ≤ 22 °c and rh∞ > 40 %, where a minimal shrinkage of droplets took place because of the hygroscopic growth of droplets. the results of this study do not imply that the covid-19 virus will be deactivated at the end of the lifetime of the droplet, but it represents that controlling the indoor environment is important for droplets to carry the virus.