Dynamic analysis of indoor carbon dioxide concentrations on a campus

Indoor air quality (IAQ) has become an emerging public health concern, particularly in densely occupied educational environments. This study investigated the temporal dynamics of indoor carbon dioxide (CO₂) concentrations in a university classroom and quantified ventilation conditions and human CO₂ emission rates under controlled and real occupancy scenarios. Continuous CO₂ monitoring was performed in three controlled experiments and five actual class sessions. The controlled experiments were conducted with seven occupants under fixed ventilation conditions, in which air conditioning was operating, windows were slightly opened, and the door was closed. Background CO₂ levels ranged from 430 to 450 ppm. After occupants entered, the indoor CO₂ concentrations increased to 610–720 ppm (1,117–1,318 mg/m³) and returned to baseline when the room was vacated.Air exchange rates (a) were calculated from the decay phase of CO₂ time-series data, yielding values between 1.60 and 1.79 h⁻¹ (mean: 1.69 ± 0.09 h⁻¹). Total CO₂ emission rates (S) were derived from the rising segment of the time-series data, resulting in values of 162–208 g/h, corresponding to per-person emission rates (SPs) of 23.1–29.5 g/h/person (mean: 25.9 ± 3.3 g/h/person), consistent with light-intensity activity.During the five monitored lectures (42–52 occupants), background CO₂ levels ranged from 440 to 470 ppm, while peak CO₂ concentrations reached 1,000–1,450 ppm (1,830–2,653 mg/m³), exceeding the regulatory limit of 1,000 ppm. The average air exchange rate during teaching sessions was 2.45 ± 0.78 h⁻¹, comparable to that in the controlled scenarios. The mean per-person CO₂ emission rate during actual classes was 20.38 ± 4.42 g/h/person, corresponding to mild activity such as sitting and listening. These findings demonstrate inadequate ventilation performance in the evaluated classroom and highlight the need for improved IAQ management in higher education institutions. This work provides actionable guidance for improving IAQ management in higher education environments.