The assessment of infection risk in indoor environments remains challenging, particularly with respect to airborne pathogens present as bioaerosols. In response to growing concerns about airborne transmission, a wide range of air cleaning technologies, including indoor room air cleaners and automotive cabin air filtration systems, have been developed to reduce human exposure.

Current standardized testing approaches predominantly rely on single-pass filtration efficiency measurements using non-biological surrogate aerosols such as plasticizer aerosols (e.g. DEHS) or mineral dusts (e.g. ISO 12103-1 A2 fine dust). While these methods provide valuable information on particle removal performance, they do not fully reflect real-life indoor conditions, where air is typically recirculated multiple times and pathogens exhibit biological properties that differ from those of inert test aerosols. Consequently, the performance of air cleaning systems under realistic multi-pass conditions and with respect to bioaerosol removal or inactivation remains insufficiently characterized, limiting their relevance for infection risk assessment.

To further explore the bioaerosol removal efficiency of air cleaning systems a new method was developed as part of the research project “AeroMobil”. Now the filtration and deactivation of viral or bacterial air pollutants is quantified in real-life conditions with a multi-pass approach As continuous air cleaning relies on the recirculation of indoor air over an extended time frame, the newly established method allows for bioaerosols to be injected into a test room where it is filtered and deactivated by the test object in recirculation by whatever mechanism of testing interest such as filtration, UV-decontamination, plasma inactivation, or others. Air sampling heads connected to a vacuum pump collect the bioaerosol particles for further microbiological analysis.

One project goal was to design the test setup in such way that allows for testing in a great variety of room configurations as well as inside of vehicle cabins and not be limited to simplified laboratory setups.

The multi-pass data generated in our test rooms and previous single-pass filtration efficiencies was integrated into a mathematical model to further expand the capabilities of air hygiene testing. This combines both results of the filter elements themselves as well as of the entire purifying machines. Known single-pass data can be entered into the model and used to calculate the theoretical performance of the air purifier in combination with the filter efficiency. The model additionally enables the upscaling of multi-pass results obtained in a test room to larger dimensions such as classrooms, while accounting for changes in room volume, the number of air purifiers, and the number of occupants, thereby allowing the impact of these parameters on aerosol concentration and infection risk to be assessed.