Predicting multiple indoor air quality parameters from spatial factors, occupant behaviours, and external conditions in single-zone urban residential units: a case study in Bangkok

Indoor Air Quality (IAQ) plays a crucial role in safeguarding occupant health and comfort, particularly in compact urban residences that lack dedicated mechanical ventilation systems and rely instead on occupant-driven ventilation practices and outdoor environmental conditions. In large tropical cities such as Bangkok, this challenge is further intensified by deteriorating outdoor air pollution, rising temperatures, and shifting indoor activity patterns in the post-pandemic era. This study introduces an integrated diagnostic framework to predict the risk of exceedance of four key IAQ parameters—temperature, relative humidity (RH), carbon dioxide (CO₂), and fine particulate matter (PM 2.5 )—based on spatial factors, real-life occupant behaviors and external climatic conditions. Field data were collected from 30 single-zone studio apartments through continuous IAQ monitoring, tracer gas decay tests, and occupant behavior logs. Analyzed models were applied to quantify the influence of different factors and classify high- and low-risk scenarios. The results indicate that keeping windows closed while operating air conditioners and air purifiers effectively maintains acceptable indoor temperature and PM 2.5 levels; however, CO₂ accumulates during periods of higher occupancy, highlighting the need for supplemental outdoor air intake. Conversely, window opening helps reduce CO₂ concentration but elevates risks of overheating, excessive humidity, and PM 2.5 exposure—particularly during the winter season when outdoor PM 2.5 levels are high. Nonetheless, nighttime during the rainy season emerges as the most favorable period for safe and energy-efficient natural ventilation. These findings provide essential empirical evidence to inform building design and operational practices, guide policy interventions, and establish a data foundation for developing adaptive ventilation strategies to sustainably improve IAQ in tropical urban environments.