Development and validation of a controlled aerosol chamber to evaluate air purifiers’ efficiency against live viral aerosols

During the COVID-19 pandemic, air-purifying devices were utilized to clear airborne viral aerosols in multi-occupancy spaces. While these devices are typically tested in confined spaces against various particulate matter, their efficiency in inactivating and removing viral aerosols has yet to be adequately assessed. Several standard methods have been published on this matter. However, this study aims to present an aerosol chamber and a novel method for evaluating the efficacy of air purifiers, specifically against viruses. MS2 bacteriophage was aerosolized inside a 19.32 m³ chamber with controlled air exchange. Viruses were sampled directly onto TSA plates, previously inoculated with MS2’s host strain, using two Slit-to-Agar devices. Particle concentrations were measured using an APS. Air exchange rates were calculated from concentration decay using APS data and culture-based methods, following ASTM-E741 standards. Comparisons were made with and without the air purifier to assess both method validity and purifier efficiency. Five sampling positions were also analyzed to evaluate chamber homogeneity. Other studies have used STA samplers and Impingers to determine the efficiency of portable air cleaners; however, these rely on multiple samplers to obtain time-dependent data. The method described in this paper enables time-dependent decay using 2 STA samplers simultaneously, thereby reducing the number of samples, testing time, and sample processing. Both viral decay and measured air exchange rates were consistent with the use of the air purifier. However, viral decay did not mirror particle decay patterns. Air exchange rates were determined by CO2 (previously) and SF6 monitoring. These differed from particle and viral decays.