# Experimental Device to Evaluate Aerosol Dispersion in Venues
###### Abstract  
The COVID-19 pandemic has focused attention on the importance of understanding and mitigating the airborne transmission of pathogens in indoor environments. This study investigated the aerosol distribution in different indoor venues with varying ventilation concepts, including displacement, mixed, and natural ventilation. A measurement system was developed to investigate venue-specific aerosol distribution patterns using a sodium chloride solution as a tracer. To analyse the spatial dispersion of aerosols, Computational Fluid Dynamics (CFD) simulations were conducted in addition to experimental investigations. The investigations indicated the lowest aerosol load for the venue with displacement ventilation and the highest for the naturally ventilated venue. The measurement system developed in this study provides a useful tool for assessing the effectiveness of ventilation measures in reducing airborne transmission of pathogens in indoor environments. It also proved its wide range of applications, as it can be used in variously sized and shaped indoor environments, with or without an audience. a 2024 24 June  
air in the occupied lower part of the room, and warm waste air in the unoccupied upper part of the room. Natural convection generates a cooling effect for the occupants, as the cool air rises and adsorbs the heat from them, which is then expelled from the room [13]. In a mixing ventilation system, fresh air is supplied to the room with a high initial mean velocity, creating a high turbulence intensity to promote good mixing of fresh and polluted air and an even distribution of temperature and pollutants throughout the venue [12; 14]. Natural ventilation is a ventilation method where natural forces, such as wind and thermal buoyancy, drive outdoor air through purpose-built building envelope openings [15]. It is a ventilation method with very low investment and operating costs compared to mechanical ventilation systems. In addition, the effectiveness of natural ventilation on the infection risk potential and climatic conditions in the room is highly dependent on the outside temperature, the wind direction, and the user [16]. Developing methods to assess the risk of airborne pathogen transmission is essential to ensure that technologies used to control and improve air quality work effectively and efficiently [1]. For individualized considerations and high levels of accuracy, experimental studies must be conducted to examine the efficacy of ventilation measures [9]. Several strategies have been proposed for investigating aerosol distribution in indoor venues, each with its own advantages and limitations. One method to directly detect SARS-CoV-2 in the air is active indoor air sampling followed by polymerase chain reaction (PCR) detection, as recently shown by [PERSON] et al. [17]. While this method attempts to capture the actual viral load under real-world conditions, it does not provide controlled boundary conditions. Another method to evaluate the spread of aerosols is the use of tracer gases. A tracer gas is emitted into the venue and local concentrations are measured using infrared spectrometers [9]. This measurement technique is convenient for both small and large venues with outside air exchange. However, the room needs to be completely free from the tracer gas of potential previous measurements to avoid contamination. Also, tracer gases cannot be filtered, making this method unsuitable for evaluating air purifiers that rely on filtration [9]. A third method to observe how particles are transported in indoor environments is the surrogate particle method, where a particle generator is used for the emission of surrogate particles. Using optical particle counters or scanning mobility particle sizes at several positions allows the spatial and temporal measurement of particle numbers, concentration, and size distribution. For this, the room to be studied needs to be initially free of particles and all potential sources of particles, including humans.