Sphagnum palustre moss bags as sentinels to monitor indoor air PAHs in university libraries

Indoor air quality in libraries impairs user health and productivity. This study first employed Sphagnum palustre moss bags as low-cost sentinels to monitor indoor polycyclic aromatic hydrocarbons (PAHs) across three university libraries differing in age and location. Moss bags were deployed for 45 days during the non-heating (autumn) and heating (winter) periods in study rooms, electronic reading rooms, stack rooms, and outdoors. Total PAH concentrations ranged from 487.20 to 1,049.86 µg/kg in autumn and 734.60 to 3,167.35 µg/kg in winter, with phenanthrene, naphthalene, pyrene, and fluoranthene as dominant congeners. Indoor-to-outdoor ratios indicated indoor sources at some sites in autumn, but outdoor infiltration in winter. Diagnostic ratios revealed petrogenic origins in autumn and mixed petrogenic/pyrogenic inputs in winter at the study room of older libraries, influenced by domestic heating. The levels, profiles, and sources of indoor PAHs varied with room function, building age and location, outdoor air quality, and season. These findings demonstrate that S. palustre moss bags are effective sentinels for detecting spatial and seasonal variations in indoor PAHs, offering a practical alternative for high-density indoor air quality monitoring.