Respiratory particles exhaled when an individual speaks and breathes can facilitate respiratory virus transmission. Portable air purification units can potentially reduce transmission risk by decreasing the overall infectious particle concentration in a room. This is particularly important for rooms with an inability to be ventilated with adequate amounts of filtered or outdoor air. While the efficacy of portable air filtration units on particle concentrations has been well-studied, the impact of portable air purification units on particle deposition and, hence, indirect aerosol transmission, has received lesser study but may be important for smaller spaces with greater surface area-to-volume ratios. We conducted a series of experiments in a simulated, small conference room (34.4 m3, mimicking a common office meeting room) assessing (1) particle removal rates and (2) changes in deposition rate owing to the presence of a low-cost box fan air purifier (BFAP). To mimic an infectious aerosol source, a breathing simulator manikin was utilized in these experiments, which ejected fluorescein tagged particles in the 1–3 μm size range throughout each experimental condition, with a prescribed, periodic, breathing waveform mimicking human exhalation. We measured deposition flux on upward- and downward-facing horizontal surfaces throughout the room and determined aerosol mass concentrations using impingers; combined, these data enabled estimates of surface-specific deposition velocities. Aerosol size distributions within the room were also quantified using an optical particle spectrometer. CFD simulations and theoretical calculations were simultaneously conducted for comparison to the experimental data. Results suggested the BFAP unit, which had an effective clean air delivery rate of 540 m3 h−1, increased the effective air exchange rate by 4.4x over baseline (20.1 vs. 4.5 h−1). Notably, BFAP unit operation introduced greater deposition to surfaces near the breathing simulator manikin vs. baseline, with deposition velocities within 2 m of the breathing simulator being 100 cm s−1 during BFAP operation, compared to 10−2 cm s−1 during baseline. Deposition velocities and air exchange rates generated from the CFD and theoretical calculations largely agreed with those derived from experiments. Taken together, data suggest that in smaller rooms, such as conference rooms, deposition is not negligible as a mechanism of aerosol clearance, even for particles near 1–3 μm in diameter.
Bibliographical noteFunding Information:
We wish to thank William Clark from Mayo Clinic Respiratory Care for allowing use of the respiratory manikin as well as Eric Heins, Well Living Lab Director of Building Operations, for assisting with continued acquisition of materials for these experiments. This specific study was funded by Delos Living LLC and Ford Motor Company, as one of the Well Living Lab's Alliance members. Delos Living LLC had no input on the study design, data collection, data analysis, or publication of this study. Ford Motor Company consulted on several technical aspects of the study given their development of the box fan air purifier described while also providing access to supercomputing resources for the CFD analyses performed. They otherwise had no input on the data collection, data analysis, or publication of this study.
The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Zachary C. Pope reports financial support was provided by Delos Living LLC . Linhao Li reports financial support was provided by Delos Living LLC . Meng Kong reports financial support was provided by Delos Living LLC . Zachary C. Pope reports financial support was provided by Ford Motor Company . Linhao Li reports financial support was provided by Ford Motor Company . Meng Kong reports financial support was provided by Ford Motor Company . Jiarong Hong reports financial support was provided by Ford Motor Company . Ruichen He reports financial support was provided by Ford Motor Company .
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