publication . Article . 2022

Transition from saliva droplets to solid aerosols in the context of COVID-19 spreading

Mehdi Stiti; Guillaume Castanet; Andrew Corber; Marcus Aldén; Edouard Berrocal;
Open Access English
  • Published: 01 Mar 2022 Journal: Environmental Research (issn: 0013-9351, eissn: 1096-0953, Copyright policy)
  • Publisher: The Authors. Published by Elsevier Inc.
  • Country: France
Abstract
To control the evolution of a pandemic such as COVID-19, knowing the conditions under which the pathogen is being transmitted represents a critical issue, especially when implementing protection strategies like social distancing and face masks wearing. For viruses and bacteria that spread via airborne and/or droplet pathways, this requires understanding how saliva droplets evolve over time after their expulsion by speaking or coughing. Within this context, the transition from saliva droplets to solid residues, due to water evaporation, is studied here both experimentally, considering the saliva from 5 men and 5 women, and via numerical modeling to accurately predict the dynamics of this process. The model assumes saliva to be a binary water/salt mixture and is validated against experimental results using saliva droplets that are suspended in an ultrasound levitator. We demonstrate that droplets with an initial diameter smaller than 21 μm will produce a solid residue that would be considered an aerosol of <5 μm diameter within less than 2 second (for any relative humidity less than 80% and/or any temperature greater than 20 °C). Finally, the model developed here accounts for the influence of the saliva composition, relative humidity and ambient temperature on droplet drying. Thus, the travel distance prior to becoming a solid residue can be deduced. We found that saliva droplets of initial size below 80 μm, which corresponds to the vast majority of speech and cough droplets, will become solid residues prior to touching the ground when expelled from a height of 160 cm.
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Subjects
free text keywords: Article, COVID-19, Airborne transmission, Saliva evaporation, Droplets, Aerosols, [SPI.FLUID]Engineering Sciences [physics]/Reactive fluid environment, General Environmental Science, Biochemistry, Aerosol, Context (language use), Relative humidity, Airborne transmission, Saliva, Coronavirus disease 2019 (COVID-19), Face masks, Saliva composition, Chemical physics, Materials science
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Funded by
EC| Spray-Imaging
Project
Spray-Imaging
Detailed Characterization of Spray Systems using Novel Laser Imaging Techniques
  • Funder: European Commission (EC)
  • Project Code: 638546
  • Funding stream: H2020 | ERC | ERC-STG
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