Determination of the optimal penetration factor for evaluating the invasion process of aerosols from a confined source space to an uncontaminated area.

Due to the outbreak and spread of COVID-19, SARS-CoV-2 has been proven to survive in aerosols for hours. Virus-containing aerosols may intrude into an uncontaminated area from a confined source space under certain ventilated conditions. The penetration factor, which is the most direct parameter for evaluating the invasion process, can effectively reflect the penetration fraction of aerosols and the shielding efficiency of buildings. Based on the observed concentrations of aerosols combined with a widely used concentration model, four numerical calculations of the penetration factor are proposed in this study. A theoretical time-correction Pest was applied to a size-dependent Pavg by proposing a correction coefficient r, and the error analysis of the real-time P(t) and the derived Pd were also performed. The results indicated that Pavg supplied the most stable values for laboratory penetration simulations. However, the time-correction is of little significance under current experimental conditions. P(t) and Pd are suitable for rough evaluation under certain conditions due to the inevitability of particles detaching and re-entering after capture. The proposed optimal penetration factor and the error analysis of each method in this study can provide insight into the penetration mechanism, and also provide a rapid and accurate assessment method for preventing and controlling the spread of the epidemic.