Unraveling the impact of operational parameters and environmental conditions on the quality of viable bacterial aerosols

Viable pathogen-laden droplets of consistent quality are essential for reliably assessing the protection offered by facemasks against airborne infections. We identified a significant gap in guidance within standardized tests for evaluating the filtration efficiencies of facemask materials using viable bacteria-laden aerosol droplets. An aerosol platform, built according to the American Society for Testing and Materials standard F2101-19, was used to validate and standardize facemask filtration test procedures. We utilized this platform to investigate the impact of varying five operating parameters, namely suspension media composition, relative humidity, pathogen concentration, and atomizer airflow and feed flow rates, on the aerosol quality of viable bacteria-laden aerosols. We achieved consistent generation of 1,700 to 3,000 viable bacteria-laden droplets sized between 2.7 and 3.3 µm under the following optimized test conditions: 1.5% w/v peptone water concentration, ≥80% relative humidity at 24 ± 2 °C, 1 × 10⁵ CFU/mL bacterial concentration, 1.5 L/min atomizer airflow rate, and 170 μL/min feed flow rate. We also explored the consequence of deviating from these optimized test parameters on viable bacteria-laden aerosol quality. These results highlight the importance of controlling these parameters when studying airborne transmission and control.