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The simulation code shows how air circulation affects aerosol spread on a bus. Simulation and visualisation: Ville Vuorinen and Heikki Kahila, Aalto University

Assistant Professor Ville Vuorinen is developing a code to vastly improve how aerosol clouds are modelled, allowing even regular desktop computers to compute the currently lengthy calculations. Aerosols are tiny airborne particles that carry pathogens, like SARS-CoV-2 virus.

‘There’s increasing research evidence that aerosols play a strong role in spreading the Corona virus. Normally modelling aerosol movement requires a super computer and, even then, it takes several days. Our program makes use of graphics cards from the gaming word, which can add so much computing power to a regular computer that we can get a result in as little as one hour,’ Vuorinen says.

The program takes into account the number of people and their positions, in addition to calculating how the space itself and ventilation systems affect how aerosol clouds form, spread, and dissipate. When ready, Vuorinen intends to make the code openly available.

‘Through this 1.5-year project we’re modelling various public spaces from sport events to public transport and schools. Our approach could offer solutions to keeping society open during a pandemic. We’ve set out to make an effective and versatile tool available in at least one programming language that helps researchers and other professionals,’ he explains.

Vuorinen is focusing on modelling indoor spaces, where the risk of an aerosol-based infection is significantly higher.

‘Aerosol concentrations easily increase in closed environments, especially when there are a lot of people gathered and there’s loud talk, yelling or singing. During an epidemic it’s wise to avoid these spaces or minimize your time there, even while wearing a mask,’ he says.

Last spring Vuorinen’s team, in collaboration with researchers from other Finnish institutions, discovered how differently sized aerosol droplets behave in the air. Until then, it was assumed that only very small, under-5 micrometre droplets stay suspended in aerosol clouds.

‘Our study found that larger droplets – as big as 50-100 micrometres – can rapidly dry up before they reach the floor and linger in the air. This has major implications for the ventilation and air circulation of public spaces, as well as for mask recommendations,’ Vuorinen adds.

The project received funding from the Academy of Finland in spring 2020.

Read the study from last spring: (sciencedirect.com)