Combined effects of evaporation, sedimentation and solute crystallization on the dynamics of aerosol size distributions on multiple length and time scales

TL;DR

This paper combines theoretical, simulation, and modeling approaches to study aerosol droplet dynamics, evaporation, and viral load implications under different environmental conditions, enhancing understanding of airborne infection risks.

Contribution

It introduces a comprehensive framework integrating evaporation, sedimentation, molecular reflection, and solute crystallization effects on aerosol behavior.

Findings

Viral load in air depends on relative humidity.

Water molecule reflection negligible at room temperature, increases at higher temperatures.

Diffuse-interface model reproduces sharp-interface features and extends analysis.

Abstract

We investigate three aspects of aerosol-mediated air-borne viral infection mechanisms on different length and time scales. First, we address the evolution of the size distribution of a non-interacting ensemble of droplets that are subject to evaporation and sedimentation using a sharp droplet-air interface model. From the exact solution of the evolution equation we derive the viral load in the air and show that it depends sensitively on the relative humidity. Secondly, from Molecular Dynamics simulations we extract the molecular reflection coefficient of single water molecules from the air-water interface. This parameter determines the water condensation and evaporation rate at a liquid droplet surface and therefore the evaporation rate of aqueous droplets. We find the reflection of water to be negligible at room temperature but to rise significantly at elevated temperatures and for grazing incidence angles. Thirdly, we derive a thermodynamically consistent three-dimensional diffuse-interface model for solute-containing droplets that is formulated as a three-phase Cahn-Hilliard/Allen-Cahn system. By numerically solving the coupled system of equations, we explore representative scenarios that show that this model reproduces and generalizes features of the sharp-interface model. These interconnected studies on the dynamics of aerosol droplet evaporation are relevant in order to quantitatively assess the airborne infection risk under varying environmental conditions.