Insights on drying and precipitation dynamics of respiratory droplets in the perspective of Covid-19

TL;DR

This study investigates the drying and precipitation behavior of respiratory droplets containing viral particles, providing insights into Covid-19 airborne transmission through experiments with surrogate fluids and validation with real samples.

Contribution

It introduces a novel experimental approach using acoustic levitation to emulate and analyze the drying dynamics of respiratory droplets containing viruses.

Findings

Final crystallite size is consistently 20-30% of initial droplet diameter.

Approximately 15% of virions remain on the surface after evaporation in airborne droplets.

Surface-evaporated droplets retain up to 90% of virions on their exterior.

Abstract

We isolate a nano-colloidal droplet of surrogate mucosalivary fluid to gain fundamental insights into the infectivity of air borne nuclei during the Covid-19 pandemic. Evaporation experiments are performed with salt-water solutions seeded with a viral load of inactive nanoparticles in an acoustic levitator. We seek to emulate the drying, flow and precipitation dynamics of such air borne mucosalivary droplets. Observations with the surrogate fluid are validated by similar experiments with actual samples from a healthy subject. A unique feature emerges with regards to the final crystallite dimension; it is always 20-30% of the initial droplet diameter for different sizes and ambient conditions. The preserved precipitates from levitated droplets show that 15% of the total virion population remain dispersed on the outer surface of air-desiccated air borne nuclei. This fraction increases to ~90% if the respiratory droplets (of larger initial size) settle on a surface and then evaporate in the sessile mode.