| Summary: | This study investigates the diel cycle of airborne microorganisms indoors and its role as a proxy for indoor air quality. Using metagenomic analysis, 124 air samples were collected and analyzed on phylum, genus, and species level classifications. The study includes samples from two offices (Office 1 and Office 2) and an outdoor setting, each taken over six days and nights. Results show a clear day-night cycle for indoor bioaerosols in Office 1, distinct from the outdoor environment, with human-associated taxa dominating during the day. Office 2, considered polluted with mold, displays a divergent taxonomic profile lacking bacterial taxa. The study highlights the influence of mechanical ventilation on indoor bioaerosol dynamics, with night-time infiltration of outdoor air leading to the equilibration of indoor and outdoor air microbiomes. Furthermore, the study examines the effect of outdoor temperature on indoor air microbiome composition, observing disruptions in the outdoor diel cycle during a period of unusually low temperatures. Finally, the efficacy of mold removal and sanitation efforts is confirmed through follow-up air sampling, indicating significant reductions in Aspergillus versicolor and airborne fungal copy numbers. This comprehensive metagenomic survey sheds light on the role of indoor bioaerosol dynamics in instigating health related issues. Inclusion of such highly-resolved bioaerosol monitoring effort into the currently established air quality standards shall provide invaluable insights on improving indoor air quality through ventilation and sanitation efforts.
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