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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
Published: 01 Mar 2022
Publisher: HAL CCSD
Country: France

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.

Subjects by Vocabulary

ACM Computing Classification System: ComputingMilieux_MISCELLANEOUS

Microsoft Academic Graph classification: Aerosol Materials science Saliva composition Saliva Context (language use) Coronavirus disease 2019 (COVID-19) Relative humidity Airborne transmission Chemical physics Face masks


[SPI.FLUID]Engineering Sciences [physics]/Reactive fluid environment, General Environmental Science, Biochemistry, [SPI.FLUID] Engineering Sciences [physics]/Reactive fluid environment, Aerosols, COVID-19, Humans, SARS-CoV-2, Saliva, Speech, Article, Airborne transmission, Saliva evaporation, Droplets

Funded by
EC| 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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