Implications of the spatiotemporal distribution of CO2 on indoor air quality: A field study with reduced-order modeling

We conducted a field study to monitor CO2 concentrations spatiotemporally in a lecture theatre, to explore its implications for Indoor Air Quality (IAQ), particularly in relation to airborne pathogen transmission. It is widely recognized that ensuring adequate ventilation in buildings can reduce the probability of airborne transmission, with indoor CO2 levels serving as a valuable indicator of ventilation effectiveness. While the temporal evolution of CO2 concentrations has been well-documented in the literature, to the best of our knowledge, the spatiotemporal distribution remains less understood, especially in large spaces (>10 m) that are poorly ventilated (air change rates below approximately 1.0 h(-)(1)) and air-conditioned buildings. Hence, we analyzed spatiotemporal CO2 variations across four cases with different occupancy levels and seating arrangements using field study data. Our data reveal how factors such as number of people and their seating configurations, asymmetrical airflow vents in a tiered seating-designed room, and buoyancy-driven ventilation flow through an open doorway influenced spatiotemporal CO2 variations for a given room geometry of our testbed. Moreover, we developed a spatiotemporal reduced-order model that can simulate the spatiotemporal distribution of pathogen quanta using real-world data of CO2 concentrations. This derived model presented a linear relationship between CO2 concentrations and pathogen dispersion. Moreover, we explore the IAQ-energy trade-off by using airborne infection probability as a proxy for health outcomes and sensible ventilation load as a proxy for energy demand. Based on this analysis, we propose design guidelines that aim to balance IAQ with energy.