Aerodynamic Size Distribution of Bacterial Aerosols in a Classroom and Its Implications for Indoor Air Quality Assessment

Educational buildings, where occupants spend a significant part of the day, require particular attention with regard to microbiological indoor air quality. In addition to determining the concentration of airborne bacteria, the analysis of the aerodynamic size distribution of bacterial aerosols is a key component of indoor air quality assessment, as it provides information on the potential deposition of particles within different regions of the respiratory tract. The aim of this study was to characterize the aerodynamic size distribution of bacterial aerosols in classroom air during normal occupancy and to evaluate the significance of the obtained results for indoor air quality assessment.
Air samples were collected in a classroom before, during, and after classes using a six-stage Andersen cascade impactor. Bacterial concentrations were expressed as colony-forming units per cubic meter (CFU/m³), and the respirable fraction was determined based on the distribution of bacterial aerosols across the individual impactor stages.
The respirable fraction accounted for 67 76% of the total concentration of culturable bacteria, making it the dominant fraction of the bacterial aerosol. Total culturable bacterial concentrations ranged from 452 to 1062 CFU/m³, whereas the concentration of the respirable fraction ranged from 306 to 797 CFU/m³, depending on the sampling location.
Changes in particle size distribution were also observed during classroom occupancy, suggesting the influence of occupant presence and activity on the emission and resuspension of bacterial aerosols.
The findings indicate that the analysis of the aerodynamic size distribution of bacterial aerosols is an important component of indoor air quality assessment and may constitute an integral part of microbiological indoor air quality evaluation. However, further validation in different educational buildings under varying occupancy scenarios is warranted.