Effects of portable air filtration on submicrometer- and micrometer-sized particle deposition and concentration in a natural ventilated skilled nursing facility

Older adults are highly vulnerable to respiratory diseases. Effective engineering controls are critical to reduce transmission risk via airborne particles, particularly in spaces where older adults reside (e.g., skilled nursing facilities; SNF). We thus investigated how recirculating portable air filtration (PAF) units and natural ventilation influenced airborne particle travel via the direct aerosol (i.e., representing airborne transmission) and indirect aerosol (i.e., representing fomite transmission) routes. A breathing simulator atomized fluorescein-tagged submicrometer- (0.6–0.7 μm) and micrometer-sized (2 μm) particles simultaneously utilizing a physiologically-correct inhalation-exhalation waveform, with the breathing simulator outlet connected to an anatomically-correct respiratory manikin. Experiments involved two SNF resident rooms, the ‘infector’ and ‘susceptible’ rooms, with the former room containing the breathing simulator (i.e., proxy infected resident) and the latter room representing a susceptible resident's room. Observations revealed that despite PAF units enhancing deposition velocities for submicrometer- and micrometer-sized particles, effective deposition fluxes of submicrometer-sized particles were significantly lower during PAF use versus the Baseline Condition. Further, PAF units increased the effective air exchange rate by ∼3.7–4.5x for submicrometer- and micrometer-sized particles, respectively, resulting in significantly lower particle concentrations (>60%) for these particle sizes versus the Baseline Condition. While natural ventilation significantly reduced submicrometer- and micrometer-sized particle concentration and deposition, cross contamination between rooms was identified when natural ventilation was the singular ventilation solution. Observations validated our previous studies in that particle deposition is non-negligible in smaller rooms with poor ventilation and that PAF units are recommended to supplement natural ventilation and best limit airborne particle concentration and deposition.