# Experimental Device to Evaluate Aerosol Dispersion in Venues
## 4 Discussion
### Features and Advantages of the Measurement System  
A major advantage of the measurement system is its wide range of applications. In contrast to other available measurement methods, it is not limited to clean rooms. The  
\begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Displacement Ventilation Venue** & **Mixing Ventilation Venue** & **Natural Ventilation Venue** \\ \hline Aerosol distribution & Aerosol plume pulling backwards over the emitter & No dominant room air flow, depending on boundary conditions Dispersion in the entire venue & Aerosol plume pulling backwards over the emitter \\ \hline Positions with high aerosol exposure & Along the aerosol plume & Forecast only possible to a limited extent & Along the aerosol plume Prediction only possible to a limited extent \\ \hline Aerosol load of the venue & Low outside of the aerosol plume & Medium, depending on the distance to the aerosol generator & High in the whole venue and highest inside of the aerosol plume \\ \hline \hline \end{tabular}
\end{table}
Table 7: Summary of the characteristics of the three investigated venues based on experimental measurements and CFD analyses.  
measurement system can perform in variously sized and shaped indoor environments, with or without audience. If the measurements are conducted without an audience, heat sources are used, ensuring a higher reproducibility compared to measurements with a human audience. It needs to be emphasized that parameters such as room temperature, relative humidity, and fluid turbulence influence the range and time aerosols are suspended in air [27; 31; 34]. For these reasons, measurement results can vary with the slightest change in the boundary conditions. However, this also applies to dispersion of pathogenic aerosol in a real case. This paper focuses on fully occupied venues where the occupants are static most of the time. The measurement system can also be used in other ways, but the results are less reproducible if the air flow is influenced by a strong movement of people.  
Since a NaCl solution is used as a tracer, the system is not harmful when used with an audience. A limitation might occur in environments where the air contains a certain concentration of conductive particles similar to the emitted tracer solution. Nevertheless, the background concentration of particles is measured anew for each measurement. Whether a room has been fully ventilated after a measurement or whether a background concentration is present can be deduced from a change in the increase in conductivity during the lead-in time, which is then subtracted from the total increase.  
To obtain the most meaningful measurement output, the positioning of the absorbers and aerosol generator at the venue is essential. Whether a tracer reaches a certain absorber in a certain time depends on the flow field. To obtain a good first impression of the global air flow for application in rooms with complex air flow, it is helpful to perform a smoke dispersion analysis before the measurements. Subsequently, particularly critical areas can be analysed by the aerosol generator and the absorbers. The measuring system can also be used to investigate the influence of hygiene measures [18], to show the influence of the supply air volume flow and to show the effect of the occupancy of an venue [19].