Humid air can extend lifetime of virus-laden aerosol droplets

August 18, 2020

WASHINGTON, August 18, 2020 -- The novel coronavirus that causes COVID-19 is thought to spread through natural respiratory activities, such as breathing, talking and coughing, but little is known about how the virus is transported through the air.

University of Missouri scientists report, in Physics of Fluids, by AIP Publishing, on a study of how airflow and fluid flow affect exhaled droplets that can contain the virus. Their model includes a more accurate description of air turbulence that affects an exhaled droplet's trajectory.

Calculations with their model reveal, among other things, an important and surprising effect of humid air. The results show high humidity can extend the airborne lifetime of medium-sized droplets by as much as 23 times.

Droplets exhaled in normal human breath come in a range of sizes, from about one-tenth of a micron to 1,000 microns. For comparison, a human hair has a diameter of about 70 microns, while a typical coronavirus particle is less than one-tenth of a micron. The most common exhaled droplets are about 50 to 100 microns in diameter.

The droplets exhaled by an infectious individual contain virus particles as well as other substances, such as water, lipids, proteins and salt. The research considered not just transport of droplets through the air but also their interaction with the surrounding environment, particularly through evaporation.

The investigators used an improved description of air turbulence to account for natural fluctuations in air currents around the ejected droplet. They were able to compare their results to other modeling studies and to experimental data on particles similar in size to exhaled droplets. The model showed good agreement with data for corn pollen, which has a diameter of 87 microns, approximately the same size as most of the exhaled droplets.

Humidity affects the fate of exhaled droplets, since dry air can accelerate natural evaporation. In air with 100% relative humidity, the simulations show larger droplets that are 100 microns in diameter fall to the ground approximately 6 feet from the source of exhalation. Smaller droplets of 50 microns in diameter can travel further, as much as 5 meters, or about 16 feet, in very humid air.

Less humid air can slow the spread. At a relative humidity of 50%, none of the 50-micron droplets traveled beyond 3.5 meters.

The investigators also looked at a pulsating jet model to mimic coughing.

"If the virus load associated with the droplets is proportional to the volume, almost 70% of the virus would be deposited on the ground during a cough," said author Binbin Wang. "Maintaining physical distance would significantly remediate the spread of this disease through reducing deposition of droplets onto people and through reducing the probability of inhalation of aerosols near the infectious source."
-end-
The article, "Transport and fate of human expiratory droplets - a modeling approach," is authored by Binbin Wang, Huijie Wu and Xiu-Feng Wan. The article will appear in Physics of Fluids on Aug. 18, 2020 (DOI: 10.1063/5.0021280). After that date, it can be accessed at https://aip.scitation.org/doi/10.1063/5.0021280.

ABOUT THE JOURNAL

Physics of Fluids is devoted to the publication of original theoretical, computational, and experimental contributions to the dynamics of gases, liquids, and complex fluids. See https://aip.scitation.org/journal/phf.

American Institute of Physics

Related Science Articles from Brightsurf:

75 science societies urge the education department to base Title IX sexual harassment regulations on evidence and science
The American Educational Research Association (AERA) and the American Association for the Advancement of Science (AAAS) today led 75 scientific societies in submitting comments on the US Department of Education's proposed changes to Title IX regulations.

Science/Science Careers' survey ranks top biotech, biopharma, and pharma employers
The Science and Science Careers' 2018 annual Top Employers Survey polled employees in the biotechnology, biopharmaceutical, pharmaceutical, and related industries to determine the 20 best employers in these industries as well as their driving characteristics.

Science in the palm of your hand: How citizen science transforms passive learners
Citizen science projects can engage even children who previously were not interested in science.

Applied science may yield more translational research publications than basic science
While translational research can happen at any stage of the research process, a recent investigation of behavioral and social science research awards granted by the NIH between 2008 and 2014 revealed that applied science yielded a higher volume of translational research publications than basic science, according to a study published May 9, 2018 in the open-access journal PLOS ONE by Xueying Han from the Science and Technology Policy Institute, USA, and colleagues.

Prominent academics, including Salk's Thomas Albright, call for more science in forensic science
Six scientists who recently served on the National Commission on Forensic Science are calling on the scientific community at large to advocate for increased research and financial support of forensic science as well as the introduction of empirical testing requirements to ensure the validity of outcomes.

World Science Forum 2017 Jordan issues Science for Peace Declaration
On behalf of the coordinating organizations responsible for delivering the World Science Forum Jordan, the concluding Science for Peace Declaration issued at the Dead Sea represents a global call for action to science and society to build a future that promises greater equality, security and opportunity for all, and in which science plays an increasingly prominent role as an enabler of fair and sustainable development.

PETA science group promotes animal-free science at society of toxicology conference
The PETA International Science Consortium Ltd. is presenting two posters on animal-free methods for testing inhalation toxicity at the 56th annual Society of Toxicology (SOT) meeting March 12 to 16, 2017, in Baltimore, Maryland.

Citizen Science in the Digital Age: Rhetoric, Science and Public Engagement
James Wynn's timely investigation highlights scientific studies grounded in publicly gathered data and probes the rhetoric these studies employ.

Science/Science Careers' survey ranks top biotech, pharma, and biopharma employers
The Science and Science Careers' 2016 annual Top Employers Survey polled employees in the biotechnology, biopharmaceutical, pharmaceutical, and related industries to determine the 20 best employers in these industries as well as their driving characteristics.

Three natural science professors win TJ Park Science Fellowship
Professor Jung-Min Kee (Department of Chemistry, UNIST), Professor Kyudong Choi (Department of Mathematical Sciences, UNIST), and Professor Kwanpyo Kim (Department of Physics, UNIST) are the recipients of the Cheong-Am (TJ Park) Science Fellowship of the year 2016.

Read More: Science News and Science Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.