Air filtration has never been under such a high public focus than it is today. during the Covid19 pandemic, especially as there is strong indication that the SARS-CoV2 virus can spread as aerosols via the air. As the virus may attach to smaller or larger particles (solid or liquid), a large range of particles sizes has to be considered from some micrometers down to the nano scale. Air handling units using high quality and efficient fine filters and by regarding specific advice given for the pandemic times do reduce the virus concentration in buildings. Together with other measures like keeping distance and wearing face masks this can reduce the infection risk significantly.