Assessment of Aerosol Persistence in ICUs via Low-cost Sensor Network and Zonal Models

Abstract

Abstract The COVID-19 pandemic heightened public awareness about airborne particulate matter (PM) due to the spread of infectious diseases via aerosols. The persistence of potentially infectious aerosols in public spaces, particularly medical settings, deserves immediate investigation; however, a systematic approach to characterize the fate of aerosols in most clinical environments has not been reported. This paper presents a methodology for mapping aerosol propagation using a low-cost PM sensor network in ICU and adjacent environments and the subsequent development of the data-driven zonal model. Mimicking aerosol generation by a patient, we generated trace NaCl aerosols and monitored their propagation in the environment. In positive (closed door) and neutral-pressure (open door) ICUs, up to 6% or 19% respectively of all PM escaped through the door gaps, however, the outside sensors did not register an aerosol spike in negative-pressure ICUs. The K-means clustering analysis of temporospatial aerosol concentration data suggests that ICU can be represented by three distinct zones: (1) near the aerosol source, (2) room periphery, and (3) the outside region. These zones inform two-phase aerosol plume behavior: dispersion of the original aerosol spike throughout the room and an evacuation phase where "well-mixed" aerosol concentration in the ICU decayed uniformly. Decay rates were calculated in positive, neutral, and negative modes, with negative-pressure rooms clearing out nearly twice as fast. The aerosol concentration decay followed the trends in the air exchange rates. This research demonstrates the methodology for aerosol persistence monitoring in medical settings; however, it is limited by a relatively small data set and is specific to small-size ICU rooms. Future studies need to evaluate medical settings with high risks of infectious disease transmission and optimize hospital infrastructure.