Humidity of exhaled breath increases lifetime of covid droplets in air

[sayak83]

This work shows that covid droplets lasts much longer due to the humidity in the exhaled air stream. Thus they can travel longer distances to potentially infect a person

Previous models assumed that only large droplets pose a relevant risk of infection because small droplets evaporate quickly. At TU Wien (Vienna), however, in cooperation with the University of Padova, it has now been shown that this is not true: Due to the high humidity of the air we breathe, even small droplets can remain in the air much longer than previously assumed. The study was published in the scientific journal PNAS.

https://medicalxpress.com/news/2021-09-droplets-coronaviruses-longer-previously-thought.html

The work did a nice series of experiments in addition to modelling.

In addition, experiments were conducted A nozzle with an electromagnetically controlled valve was installed in a plastic head to spray a mixture of droplets and gas in a precisely defined manner. The process was recorded with high-speed cameras, so it was possible to measure exactly which droplets remained in the air and for how long. Francesco Picano's team at the University of Padua was also involved in the research project.

So one should not think one is safe just because they are more than 6 ft away from other ppl in public.

 

[Kangaroo Feathers]

Makes sense.

 

[ChristineM]

I read some work early on in the pandemic about how far the virus can travel suspended in exhaled droplets of moisture. It was around 18 metres.

Sorry. I can't find the paper now.

 

[Twilight Hue]

This work shows that covid droplets lasts much longer due to the humidity in the exhaled air stream. Thus they can travel longer distances to potentially infect a person



https://medicalxpress.com/news/2021-09-droplets-coronaviruses-longer-previously-thought.html

The work did a nice series of experiments in addition to modelling.

So one should not think one is safe just because they are more than 6 ft away from other ppl in public.

I think there are a lot of things in the air.

How did they test that anyways? Viruses require a full panel to identify.

 

[Wandering Monk]

If you all will remember, early guidance for social distancing was do not come within 2 meters for more than 15 minutes. The 2 meters was because larger droplets, which had high concentrations of the virus, would not travel that far. The 15 minutes was for the aerosols that could travel long distances but had lower concentrations of the virus, but which could accumulate in the air over time.

 

[sayak83]

I think there are a lot of things in the air.

How did they test that anyways? Viruses require a full panel to identify.

Virus particles are in the exhaled saliva droplets. They tracked the droplets and how long it takes for them to evaporate after getting exhaled.

 

[Wandering Monk]

Virus particles are in the exhaled saliva droplets. They tracked the droplets and how long it takes for them to evaporate after getting exhaled.

For clarity, you need to distinguish between droplets and aerosols. They are orders of magnitude different in size and also in how much virus they carry. Aerosols (what you are calling virus particles and droplets) are airborne and can travel long distances and accumulate in the air in the environment. Droplets in the sense used in most discussion are larger and don't travel very far and are easily trapped by most masks. Aerosols are NOT trapped by the mask.

 

[sayak83]

For clarity, you need to distinguish between droplets and aerosols. They are orders of magnitude different in size and also in how much virus they carry. Aerosols (what you are calling virus particles and droplets) are airborne and can travel long distances and accumulate in the air in the environment. Droplets in the sense used in most discussion are larger and don't travel very far and are easily trapped by most masks. Aerosols are NOT trapped by the mask.

This is somewhat correct. While small (micro-scale) droplets are called aerosols, not all aerosols are droplets. Aerosols can be suspension of micro or nanoscopic solid particles as well. Here when the scientists are looking at evaporation lifetimes, they look at micro-droplets.