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Physics Colloquium - Dr. Jorgen Jensen

This is a past event.

Virtual Event

Thursday, November 12, 2020, 4 pm– 5 pm

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This is a past event.

of National Center for Atmospheric Research (NCAR) will give a talk titled "The Physics of Evaporating Human-Exhaled Drops and Possible Implications for Virus Viability" on Thursday, November 12th at 4:00pm via Zoom. 

Abstract: Human-exhaled drops are thought to be a main way to transport Sars-CoV-2 virus particles from COVID-19 infected persons to other persons, thereby rendering them possible to also become infected. The viability of virus particles in airborne drops depends on a number of physical properties, e.g., air temperature, exposure to ultraviolet light, and relative humidity of air.

Human-exhaled drops share some similarities with sea-spray drops; they both originate as dilute saline solutions, and both may have an organic component. Sea water contains about 3.5% salts, and human-exhaled drops have about 1% salts (electrolytes). Sea-spray aerosols may contain organic material from marine biological decay, and human-exhaled drops contain about 1-5% organic material (proteins, lipids, etc.).

Drawing on prior studies of sea-spray, the present talk focuses on the hygroscopic properties of human-exhaled drops and how these depend on relative humidity. As a human-exhaled drop partially evaporates, the concentration of electrolytes increases. It has been hypothesized that high salinity leads to rapid reduction in virus viability, i.e., under high salinity, the virus particles are breaking down and becoming less capable of causing infection.

The hypothesis is that (i) virus viability remains high for human drops in high relative humidity air (dilute salt solution), (ii) virus viability is low for drops in intermediate relative humidities (drops are concentrated salt solutions), and (iii) virus viability is high for drops in very dry environments (electrolytes have effloresced to form salt crystals).

As human exhaled drops contain a complex mixture of electrolytes and organic material, this talk uses microscopy to examine the efflorescence process of different salts in human-exhaled drops. The goal is to determine a relative humidity range, that keeps drops as concentrated salt solutions. In the future, this may be used to guide hospitals and other public buildings to control relative humidity to values that are optimal for reducing virus viability in human-exhaled drops.


Bio: Dr. Jorgen Jensen is currently a scientist at the National Center for Atmospheric Research (NCAR)/Earth Observing Laboratory (EOL) Research Aviation Facility in Boulder, Colorado. He leads the Science and Instrumentation Group (RSIG) and his primary responsibility includes NCAR’s suite of in-situ cloud microphysics instrumentation. His research interests include aerosol-cloud interaction, in particular the warm rain process. Dr. Jensen received his PhD from University of Washington, Seattle, WA in civil engineering and his MS degree from University of Copenhagen, Denmark in physical geography.

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  • Xin Xi
  • David Holden
  • Kartik Keshava Iyer

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