Spatiotemporal Variations of Indoor PM_2.5 Concentrations in Nanjing, China

Indoor fine particulate matter (PM_2.5) is important since people spend most of their time indoors. However, knowledge of the spatiotemporal variations of indoor PM_2.5 concentrations within a city is limited. In this study, the spatiotemporal distributions of indoor PM_2.5 levels in Nanjing, China were modeled by the multizone airflow and contaminant transport program (CONTAM), based on the geographically distributed residences, human activities, and outdoor PM_2.5 concentrations. The accuracy of the CONTAM model was verified, with a good agreement between the model simulations and measurements (r = 0.940, N = 110). Two different scenarios were considered to examine the building performance and influence of occupant behaviors. Higher PM_2.5 concentrations were observed under the scenario when indoor activities were considered. Seasonal variability was observed in indoor PM_2.5 levels, with the highest concentrations occurring in the winter and the lowest occurring in the summer. Building characteristics have a significant effect on the spatial distribution of indoor PM_2.5 concentrations, with multistory residences being more vulnerable to outdoor PM_2.5 infiltration than high-rise residences. The overall population exposure to PM_2.5 in Nanjing was estimated. It would be overestimated by 16.67% if indoor exposure was not taken into account, which would lead to a bias in the health impacts assessment.