In public spaces, a portable device can calculate aerosol concentrations.
Understanding aerosol concentrations and persistence in public spaces can help assess infection risks because of the role they play in coronavirus transmission. It is difficult, however, to quantify these concentrations and requires specialist personnel and equipment.
Until now, that is.
Researchers from the Netherlands Cardiology Center and the University of Amsterdam have shown that, for this reason, a commercially available, compact particle counter can be used to help assess the effect of risk-reducing steps, such as improved ventilation.
In Physics of Fluids, from AIP Publishing, they explain the fast and simple portable method.
When using portable particle counters, the main difficulty is coping with the background dust that is prevalent in public spaces.
The question then becomes whether it is possible to distinguish these dust particles from aerosols produced by breathing, talking, sneezing and coughing.
Since dust and aerosols inhaled into the human lungs vary in size, by measuring dust over a period of time and studying how the signal shifts when aerosols are introduced to the mix, researchers developed a way to deduct the dust signal from the particle counter.
There’s a lot of particulate matter, but in that range we can’t really measure aerosols, but there’s a fair range of scale where you can detect aerosols,”There’s a lot of particulate matter, so we can’t really measure aerosols in that range, but there’s a reasonable size range where you can detect the aerosols,”
They used laboratory-based methods to compare aerosol concentrations calculated by this approach and found that the results matched perfectly.
While this paper focuses on one specific handheld particle counter, the Fluke 985, which is used for clean-room dust and air quality monitoring, Bonn notes that the findings are not exclusive to that instrument and can be generalized to other particle counters.
Since the method does not calculate the presence of virus particles directly, it is possible to combine the observed aerosol concentration with virus data from other studies in order to provide a realistic risk assessment for a specific form of public space.
The findings show that in well-ventilated environments, aerosol concentrations can be more than 100 times lower than in poorly ventilated areas, such as public elevators or toilets.
There are individuals who are worried about going to the gym, going to the workplace or taking the train.
All of that can be measured at least,’ said Bonn. “The motto remains ventilate, ventilate, ventilate.”
He said aerosols are not the only route to infection, though indoor ventilation plays a large role, and social distance and hand washing remain important.
“Reference: “Measurement using handheld particle counters for small droplet aerosol concentrations in public spaces” by G.
Cees J. M., Aernout Somsen, Stefan Kooij, van Rijn, Reinout A.
Bem and Daniel Bonn, Physics of Fluids, December 22, 2020. DOI: 10.1063/5.0035701.