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Updated: Apr 20, 2026
Composition and Distribution Analysis of Bioaerosols Under Different Environmental Conditions
Published on: January 7, 2019
Characterizing airborne fungal and bacterial concentrations and emission rates in six occupied children's classrooms
D Hospodsky1, N Yamamoto1,2, W W Nazaroff3
1Department of Chemical and Environmental Engineering, Yale University, New Haven, CT, USA.
Unlabelled:
Baseline information on size-resolved bacterial, fungal, and particulate matter (PM) indoor air concentrations and emission rates is presented for six school classrooms sampled in four countries. Human occupancy resulted in significantly elevated airborne bacterial (81 times on average), fungal (15 times), and PM mass (nine times) concentrations as compared to vacant conditions. Occupied indoor/outdoor (I/O) ratios consistently exceeded vacant I/O ratios. Regarding size distributions, average room-occupied bacterial, fungal, and PM geometric mean particle sizes were similar to one another while geometric means estimated for bacteria, fungi, and PM mass during vacant sampling were consistently lower than when occupied. Occupancy also resulted in elevated indoor bacterial-to-PM mass-based and number-based ratios above corresponding outdoor levels. Mean emission rates due to human occupancy were 14 million cells/person/h for bacteria, 14 million spore equivalents/person/h for fungi, and 22 mg/person/h for PM mass. Across all locations, indoor emissions contributed 83 ± 27% (bacteria), 66 ± 19% (fungi), and 83 ± 24% (PM mass) of the average indoor air concentrations during occupied times.
Practical Implications:
An extensive data set of bacterial and fungal size-distributed indoor air concentrations and emission rates is presented. Analysis of these data contributes to an understanding of how indoor bacterial and fungal aerosols are influenced by human occupancy. This work extends beyond prior culture and DNA-based microbiome studies in buildings to include quantitative relationships between size-resolved bacterial and fungal concentrations in indoor air and building parameters such as occupancy, ventilation, and outdoor conditions. The work indicates that occupancy-associated emissions (e.g., via resuspension and shedding) contribute more to both bacterial and fungal indoor air concentrations than do outdoor sources for the occupied classrooms investigated in this study.
Insights
Human occupancy significantly increases indoor airborne bacteria, fungi, and particulate matter (PM) in classrooms. Occupant emissions contribute substantially more to indoor air concentrations than outdoor sources.
Area of Science:
- Environmental Science
- Microbiology
- Air Quality
Background:
- Indoor air quality is influenced by various factors, including human activity.
- Understanding the sources and characteristics of indoor aerosols is crucial for public health.
Purpose of the Study:
- To quantify size-resolved bacterial, fungal, and particulate matter (PM) concentrations and emission rates in occupied and vacant school classrooms.
- To investigate the impact of human occupancy on indoor aerosol levels and characteristics.
Main Methods:
- Sampling of size-resolved bacteria, fungi, and PM in six school classrooms across four countries.
- Comparison of aerosol concentrations and size distributions during occupied versus vacant conditions.
- Calculation of indoor emission rates per person for bacteria, fungi, and PM mass.
Main Results:
- Human occupancy significantly elevated airborne bacteria (81x), fungi (15x), and PM mass (9x) compared to vacant conditions.
- Occupancy increased indoor/outdoor ratios for all measured aerosols.
- Indoor emissions accounted for 83% of bacterial, 66% of fungal, and 83% of PM mass concentrations during occupied times.
Conclusions:
- Human occupancy is a dominant factor influencing indoor bacterial and fungal aerosol concentrations in classrooms.
- Occupancy-associated emissions (shedding, resuspension) contribute more to indoor air levels than outdoor sources.
- This study provides quantitative data linking indoor aerosols to human occupancy and building parameters.
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