The effectiveness of using personalized ventilation (PV) in mitigating airborne transmission risk was found to be easily affected by multiple factors. The aim of this study was hereby to evaluate the impacts of several important factors on the performance of PV in airborne disease control for closely ranged occupants. Orthogonal experiments were designed for CFD simulations under different levels of four selected factors. Results indicated that the order of significance of these four factors affecting the intake fraction (IF) of the exposed occupant was as follows: mode of PV use > relative distance between occupants > PV airflow volume > background ventilation. The best combination of the four tested factors was PV of 15 L/s for both the infected source and the exposed occupant, with a relative distance of 2 m between them and mixing ventilation, which would yield an IF of merely 0.0246%. The worst combination was PV of 6 L/s for the exposed occupant only, with a relative distance of 0.86 m under displacement ventilation, indicating an elevated IF of 0.2919%. The increase of PV air volume and relative separation distance both contributed to lower exposure risk, but they were not as influential as the mode of PV use. PV integrated with mixing ventilation and utilized for both infected and susceptible occupants were recommended. The findings in this study will be helpful to provide guidance for the implementation of PV in indoor environment for airborne infection control.

Origin of differently sized respiratory droplets is fundamental for clarifying their viral loads and the sequential transmission mechanism of SARS-CoV-2 in indoor environments. Transient talking activities characterized by low (0.2 L/s), medium (0.9 L/s), and high (1.6 L/s) airflow rates of monosyllabic and successive syllabic vocalizations were investigated by computational fluid dynamics (CFD) simulations based on a real human airway model. SST k–ω model was chosen to predict the airflow field, and the discrete phase model (DPM) was used to calculate the trajectories of droplets within the respiratory tract. The results showed that flow field in the respiratory tract during speech is characterized by a significant laryngeal jet, and bronchi, larynx, and pharynx–larynx junction were main deposition sites for droplets released from the lower respiratory tract or around the vocal cords, and among which, over 90% of droplets over 5 μm released from vocal cords deposited at the larynx and pharynx–larynx junction. Generally, droplets’ deposition fraction increased with their size, and the maximum size of droplets that were able to escape into external environment decreased with the airflow rate. This threshold size for droplets released from the vocal folds was 10–20 μm, while that for droplets released from the bronchi was 5–20 μm under various airflow rates. Besides, successive syllables pronounced at low airflow rates promoted the escape of small droplets, but do not significantly affect the droplet threshold diameter. This study indicates that droplets larger than 20 μm may entirely originate from the oral cavity, where viral loads are lower; it provides a reference for evaluating the relative importance of large-droplet spray and airborne transmission route of COVID-19 and other respiratory infections.