On the Utility of a Well-Mixed Model for Predicting Disease Transmission on an Urban Bus

TL;DR

This study compares detailed airflow simulations with the simplified well-mixed model to assess airborne disease transmission risk on an urban bus, revealing significant differences especially at low ventilation rates.

Contribution

It demonstrates the limitations of the well-mixed model in predicting aerosol concentrations in enclosed spaces like buses, highlighting the importance of detailed airflow modeling.

Findings

Well-mixed model overestimates far from infected passenger at low ventilation.

Well-mixed model underestimates near infected passenger.

Simulation results apply to other enclosed spaces.

Abstract

The transport of virus-laden aerosols from a host to a susceptible person is governed by complex turbulent airflow, and physics related to breathing, coughing and sneezing, mechanical and passive ventilation, thermal buoyancy effects, surface deposition, masks, and air filtration. In this paper, we study the infection risk via airborne transmission on an urban bus using unsteady Reynolds-Averaged Navier--Stokes equations and a passive-scalar model of the virus-laden aerosol concentration. Results from these simulations are directly compared to the widely-used well mixed model, and show significant differences in the concentration field and number of inhaled particles. Specifically, in the limit of low mechanical ventilation rate, the well-mixed model will over-predict concentration far from the infected passenger, and substantially underpredict concentration near the infected passenger. The results reported herein also apply to other enclosed spaces.