On the track of aerosols — Fraunhofer vs. Corona

What role do respiratory aerosols play in the corona pandemic, how do they spread indoors, and what protective measures help effectively?

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Classrooms are a prime example of indoor spaces where many people gather every day over a long period of time.

Transmission of the SARS-CoV-2 virus can occur not only via larger droplets emitted when sneezing or coughing, but also via very small aerosol particles produced primarily when speaking or breathing. This transmission route is of great importance because aerosol particles can spread over long distances due to their long residence time in the air and thus accumulate over time, especially in poorly ventilated indoor spaces.

In this context, the dispersion and distribution of aerosols depends on the typical flow conditions in the indoor spaces under consideration, which are very different in aircraft cabins, open-plan offices or classrooms. Therefore, effective and practicable protective measures are needed that consider the specifics of the corresponding indoor spaces. While air conditioning systems in aircraft cabins can make a valuable contribution to indoor hygiene by supplying fresh air and appropriately filtered recirculated air, only a very small number of schools in Germany have central ventilation systems. This raises the question of how to effectively counteract the accumulation of aerosol particles and thus reduce the risk of infection.

Therefore, we used experimental methods, detailed literature studies on respiratory aerosols, and complex numerical flow simulations to shed more light on aerosol dispersion using a classroom as an example: This allowed us to systematically investigate the effectiveness of window ventilation options and, most importantly, the effect of a room air cleaner and the influence of its positioning on aerosol concentration.



The investigations show: Room air cleaners and proper ventilation can significantly reduce indoor aerosol concentrations and thus significantly reduce the risk of infection. Looking to the future, the topic of indoor air hygiene should be given appropriate priority in the planning and implementation of renovation and new construction projects — and not just for school buildings.

By the way, the methods developed can, in principle, also be applied to other indoor spaces, such as theaters, supermarkets and aircraft cabins. Voluntary homework: Why not visit our German website to find out more about our work in the AVATOR project?