Development and Calibration of a Multizone CONTAM Model for Indoor PM2.5 Dynamics in Central Asian Social Housing Under High Ambient Pollution

Indoor air quality in Central Asian social housing remains understudied despite high ambient air pollution and growing concern over housing-related health inequalities. This study developed and calibrated a multizone CONTAM model to simulate hourly indoor PM2.5 dynamics in a representative, naturally ventilated, occupied social housing apartment in Almaty, Kazakhstan, during the winter heating season. The model included measured outdoor PM2.5 concentrations, local meteorological data, construction drawings, literature-derived leakage values, and occupancy schedules based on household interviews. Calibration was performed iteratively across 360 model versions, and performance was evaluated using ASTM D5157-19 model-evaluation criteria. The final calibrated model met NMSE and FB (NMSE = 0.21, FB = 0.08) criteria with FS just outside the |FS| ≤ 0.50 limit (FS = −0.51), but not the correlation, slope or intercept criteria (r = 0.86, M = 0.66, b = 43% of the mean observed concentration). Baseline simulations showed significant spatial and seasonal variation in PM2.5 concentrations. During winter, simulated average PM2.5 concentrations were 41.81 µg/m³ in the living room and 220.59 µg/m³ in the kitchen, with cooking peaks exceeding 1000 µg/m³. Warmer season simulations indicated weaker stack-driven ventilation and greater interzonal pollutant transfer. These findings show that calibrated multizone modelling can characterize PM2.5 transport in occupied social housing and provide a basis for evaluating retrofit and policy interventions to reduce PM2.5 exposure among vulnerable populations.