Indoor and outdoor microbiological air quality in naturally and mechanically ventilated university libraries

Microbiological air pollutants i.e. airborne bacteria and fungi in public libraries are a potential risk to human health and paper heritage. The present study aims to investigate the variation of indoor and outdoor microbial air quality in the libraries of a public university in relation to ventilation system type, microenvironmental conditions and outdoor microbial concentrations. To determine the bacterial and fungal concentrations, air samples were collected on TSA and PDA media respectively. Fungal and bacterial concentrations ranged within 20-250 CFU/m3 and 20-230 CFU/m3 in indoor and 280-510 CFU/m3 and 20-100 CFU/m3 in the outdoor, respectively. Indoor/Outdoor ratio was lower than 1 for fungi and exceeded 1 for bacteria, indicating that outdoor (plants, soil, waste food, etc.) is the main source of fungi whereas, for bacteria, it is indoor (occupants and their activities). Penicillium spp. (43.6%), Cladosporium spp. (30.5%), and Aspergillus spp. (13%) were found as the dominant fungal genera whereas Bacillus spp. (35%), Staphylococcus spp. (23%), and Micrococcus spp. (18%) were prevailing in monitored libraries. Considering much higher (almost 15 times) occupancy in the library with central mechanical heating ventilation and air conditioning (HVAC) system, the airborne bacterial and fungal concentrations were expected to be higher accordingly. However, the concentration were comparable to those in the buildings facilitated with natural ventilation which indicate that better performance of centralized HVAC system helped neutralizing the effect of higher occupancy on air quality..

Automated summary

The study found a difference in indoor and outdoor microbial air quality in public university libraries, with bacteria and fungi mainly originating from indoor activities and outdoor environments respectively. The indoor/outdoor ratio was less than 1 for fungi and higher than 1 for bacteria.