Spatiotemporal variability of PM2.5 infiltrations in higher education buildings: A multizone air-thermal co-simulation analysis

Exposure to outdoor-sourced PM2.5 infiltration poses significant health risks to occupants of Higher Education Institution (HEI) buildings. Unlike residential settings, HEI buildings are complex and heterogeneous, presenting unique challenges for comprehensive Indoor Air Quality (IAQ) assessment. This study addresses this gap by employing a novel high-resolution multizone air-thermal co-simulation approach to investigate PM2.5 infiltration dynamics across 2,729 zones from an HEI building stock, which is crucial when consistent long-term monitoring data is unavailable. Hourly time series data reveal significant spatial and temporal variations in indoor PM2.5 concentrations and air change rates (ACHINF), underscoring the necessity of room-level resolution for accurate assessment in HEI environments. Our results demonstrate a clear positive impact of improving building airtightness (Q50) on indoor PM2.5 levels. For instance, reducing Q50 from 13 m3/h/m2 (leaky) to 3 m3/h/m2 (well-sealed) significantly decreased zones exceeding the WHO 2005 guideline (10 μg/m3) from 82% to merely 1%. Crucially, the study also revealed that outdoor PM2.5 background concentrations in the study location already frequently exceeded WHO 2005 annual guidelines (e.g., an average of 17.04 μg/m3 during the heating season). Consequently, even with well-sealed buildings (Q50=3 m3/h/m2), a significant proportion (approaching 88%) of zones still exceeded the more stringent WHO 2021 guideline of 5 μg/m3. These findings underscore the critical interplay between building airtightness and ambient pollution levels in determining indoor air quality and highlight the limit of what airtightness alone can achieve in highly polluted outdoor environments.