Dynamics of respiratory droplets carrying SARS-CoV-2 virus in closed atmosphere

From the epidemiological point of view, the lifetime of cough and sneeze droplets in the ambient atmosphere plays a significant role in the transmission rate of Coronavirus. The lifetime of indoor respiratory droplets, per se, is a function of droplet size, ambient temperature, and humidity. In the attempt to explore the effective factors of droplet lifetime, sufficient knowledge of atomic-scale interactions and dynamics of the droplet with themselves, as well as the airflow molecules in the room space, is necessary. In this study, the vertical traveling of a wide range (100 nm-10 μm) of representative carrier droplets is studied in three ambient temperatures of 258, 298, and 318 K using all-atom molecular dynamics simulation. Our obtained results confirm that by increasing the room temperature, the suspending time of aerosol (suspended droplets carrying virus particles) increases due to the higher dynamics of air and evaporated water molecules in room space. In fact, by increasing the indoor temperature, the collision rate of aerosol and ambient atmosphere molecules increases significantly. Our result shows this higher rate of collision could have a dual effect on the lifetime of aerosol considering the fact of faster deposition of larger (heavier) droplet due to the gravitational force. On one hand, in higher temperatures, the higher collision can split the droplets to smaller ones with a semi-permanent suspension period. On the other hand, the higher dynamics of ambient molecules can lead to meet and coalesce of smaller cough/sneeze droplets making larger (heavier) droplets with faster sediment times. So, the role of indoor humidity to fuel the probability of coalescence phenomenon and lifetime of droplets becomes more determinant in the warmer spaces.