We provide research findings on the physics of aerosol and droplet dispersion relevant to the hypothesized aerosol transmission of SARS-CoV-2 during the current pandemic. We utilize physics-based modeling at different levels of complexity, along with previous literature on coronaviruses, to investigate the possibility of airborne transmission. The previous literature, our 0D-3D simulations by various physics-based models, and theoretical calculations, indicate that the typical size range of speech and cough originated droplets ( ) allows lingering in the air for ) so that they could be inhaled. Consistent with the previous literature, numerical evidence on the rapid drying process of even large droplets, up to sizes , into droplet nuclei/aerosols is provided. Based on the literature and the public media sources, we provide evidence that the individuals, who have been tested positive on COVID-19, could have been exposed to aerosols/droplet nuclei by inhaling them in significant numbers e.g. . By 3D scale-resolving computational fluid dynamics (CFD) simulations, we give various examples on the transport and dilution of aerosols ( ) over distances in generic environments. We study susceptible and infected individuals in generic public places by Monte-Carlo modelling. The developed model takes into account the locally varying aerosol concentration levels which the susceptible accumulate via inhalation. The introduced concept, ’exposure time’ to virus containing aerosols is proposed to complement the traditional ’safety distance’ thinking. We show that the exposure time to inhale aerosols could range from to or even to depending on the situation. The Monte-Carlo simulations, along with the theory, provide clear quantitative insight to the exposure time in different public indoor environments.

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This study presents extensive experimental measurements in a modern Finnish ice rink arena including temperature, relative humidity, carbon dioxide, air speed, air flow and pressure difference measurements in addition to smoke tests. Furthermore, the air exchange rate (ACH), air-exchange efficiency, and mixing factor were calculated. The main aim was to determine ventilation effectiveness, vertical stratification of the air and how commonly recirculation can be used in a modern ice rink arena representing common practice. Results show that re-circulation of return air was virtually continuous and in normal operating conditions the outdoor air fraction of the supply air was only 3.7 % corresponding to ACH of 0.03 1/h. The ceiling distributed mixing ventilation was not able to mix the whole volume sufficiently, leading to two imperfectly mixed zones with an average air-exchange efficiency of 39 % in the lower zone, corresponding to a mixing factor of 1.7.

Airflow characteristics were studied with asymmetrically distributed heat load and diffuse ceiling ventilation. The heat load was gradually increased from 40 to 80 W/floor-m 2 while the target temperature of exhaust air was kept at 26±0.5°C. Experiments were carried out in a test room by conducting measurements with omnidirectional anemometers, data loggers and marker-smoke visualizations. The heat load consisted of two opposite workstations next to heated window panels in the perimeter area. The other side of the room was an open area describing a corridor zone. The workstation had a seated test dummy with laptop and monitor. The results indicate that asymmetrical heat load distribution creates a large-scale circulating airflow pattern from the heat sources to the opposite side of the room. Furthermore, the mean air speed and the airflow fluctuation increased with heat load and supply airflow rate. Consequently, also the turbulent kinetic energy and the turbulence dissipation increased. However, heat load had only a small effect on the turbulence intensity and the fluctuation energy ratio. Therefore, draught rate increased significantly with mean air speed. The observed results agree mainly with the symmetrical results otherwise, except for the systematic large-scale circulation that was not found in the symmetrical test case. The maximum draught rate was 18-21 % indicating the category B-C of thermal

The influence of occupants'’ movements should be considered when analysing local thermal comfort. This study presents the effect of human movement on airflow characteristics and local thermal conditions with diffuse ceiling ventilation by experimental studies. A simulated person moving was used to study the human movement in an office. In these experiments, three moving speeds were studied: 0.3, 0.6 and 1.0 m/s. The simulated person moved in four cycle patterns: continuous moving and with 5 s, 10 s and 15 s interval breaks between each turn. Three heat gain levels of 40, 60 and 80 W/m2 were evaluated in the chamber. The results indicate that the human movement decreased vertical temperature gradient compared with the steady-state condition. Instead, the moving intervals would have no effect on the vertical air temperature gradient. The power spectral density was increased by 90% due to the person movement compared with the steady-state condition. The moving person would create different micro-environments close to work stations than close to the moving area.