Simulation of Exhaled Droplets and Their Evolution in Common Indoor Environments
SANIKA NISHANDAR, Yucheng He, Marko Princevac, Rufus Edwards,
University of California, Riverside Abstract Number: 613
Working Group: Aerosol Science of Infectious Diseases: What We Have Learned and Still Need to Know about Transmission, Prevention, and the One Health Concept
AbstractCOVID-19 pandemic has highlighted the importance of understanding virus transmission in community settings. Computational Fluid Dynamics (CFD) enables systematic examination of the trajectories and roles the exhaled droplets play in the spread of SARS-CoV-2 in indoor environments. Experimentally measured droplet size distributions exhaled during speaking and coughing were used to simulate droplet dispersion, evaporation, and deposition in a supermarket checkout area and car where close proximity to individuals is common. The exhaled droplets only partially evaporate and stay suspended as terminal nuclei. The trajectories of the residual nuclei of size 0.3µm, based on measured peak concentrations for SARS-CoV-2 RNA in aerosols, were also simulated. Using standards for ventilation and comfort in the supermarket and car, simulations demonstrate that exhaled droplets with diameters smaller than 20μm evaporate and leave residual droplet nuclei which remain aerosolized in the air. Subsequently ~30% of these aerosolized nuclei deposit in the supermarket as well as the car, with remainder of the nuclei eventually being vented. The maximum surface deposition was 2 and 819 nuclei m
-2 for speaking and 18 and 1387 nuclei m
-2 coughing in the supermarket and car respectively. But the distribution of viral RNA is not linear across droplet sizes and larger exhaled droplets that deposit on surfaces have low viral content. Average surface deposition of viral RNA was 44 and 237 copies m
-2 for speaking and 2988 and 12539 copies m
-2 for coughing in the supermarket and car respectively. The initial airborne concentration of viral RNA was 7 × 10
6 copies per ml. Integrating the droplet statistics with viral load distributions, this study helps explain the apparent importance of inhalation exposures compared to surface contact observed in the pandemic.