Special Issue on Air Quality in a Changed World: Regional, Ambient, and Indoor Air Concentrations from the COVID to Post-COVID Era (I)

Tobias Rüggeberg1, Ana Milosevic2, Patrick Specht1, Andreas Mayer3, Joachim Frey4, Alke Petri-Fink2, Heinz Burtscher This email address is being protected from spambots. You need JavaScript enabled to view it.1,3, Barbara Rothen-Rutishauser This email address is being protected from spambots. You need JavaScript enabled to view it.2

1 Institute for Sensors and Electronics, Swiss University of Applied Sciences and Arts Northwestern Switzerland, 5210 Windisch, Switzerland
2 Adolphe Merkle Institute (AMI), University of Fribourg, 1700 Fribourg, Switzerland
3 NanoCleanAir GmbH, 5443 Niederrohrdorf, Switzerland
4 Vetsuisse Faculty, University of Bern, 3012 Bern, Switzerland

Received: August 30, 2021
Revised: October 22, 2021
Accepted: October 29, 2021

 Copyright The Author(s). This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are cited.

Download Citation: ||https://doi.org/10.4209/aaqr.210224  

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Cite this article:

Rüggeberg, T., Milosevic, A., Specht, P., Mayer, A., Frey, J., Petri-Fink, A., Burtscher, H., Rothen-Rutishauser, B. (2021). A Versatile Filter Test System to Assess Removal Efficiency for Viruses in Aerosols. Aerosol Air Qual. Res. 21, 210224. https://doi.org/10.4209/aaqr.210224


  • A system to test filter efficiencies for aerosol virus surrogates is presented.
  • MS2 bacteriophages as surrogate viruses were released in an air stream.
  • Filter efficiencies of > 99% were achieved for MS2 bacteriophages.
  • Survival of MS2 bacteriophages on the filter material decreases within days.


Mitigation measures to reduce indoor transmission of SARS-CoV-2 and other pathogenic microorganisms are urgently needed to combat the current pandemic and to prevent future airborne epidemics or pandemics. Very efficient exhaust filters for nanoparticles down to sizes of only a few nanometers have been available for many years; they are used, for example, in diesel and, more recently, gasoline vehicles to reduce emissions. The size of soot particles emitted by combustion engines, i.e., primary particles and aggregates, includes those of viruses. Therefore, such particle filters should also efficiently remove viruses. This study aimed to design a filter test system with a controlled airflow allowing to aerosolize particles at the aerosol inlet and collect samples before and after the particle filter.

As an example, results obtained for the NanoCleaner®, a filter designed to clean cabin air in vehicles, are presented. Validation with soot particles produced with a CAST soot generator revealed a filter efficiency higher than 99.5%. To assess the relevance of the test filter system to measure efficiency for viral particles removal, MS2 bacteriophages, also called Escherichia virus MS2, were used as virus surrogate and aerosolized into the filter test system with the commercially available Emser nebulizer. Filter efficiencies of more than 99% for MS2 bacteriophages were achieved using the NanoCleaner® in the filter test system. Experiments with ceramic wall-flow filters showed similar results. To enlighten the versatility of the filter test system, a typical aircraft cabin air filter was also characterized. The measurements confirmed the high filter efficiency, and in addition, we show a decrease of bacteriophage’s survival on the filter material over 48 h post-exposure.

In conclusion, we have established a versatile system that is modular to test any filter system for the efficiency of eliminating MS2 bacteriophages as virus surrogates from air.

Keywords: Particle filter, MS2 bacteriophages, Virus aerosols, Filter efficiency, Filter test system

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