Influence of kindergarten dormitory bed layout on the proximity propagation characteristics of exhaled pollutants

Kindergarten dormitories are indoor napping areas where preschool children spend extended periods nearby, making them high-risk environments for the transmission of respiratory diseases. To understand the transmission characteristics of respiratory pollutants, particularly CO₂ and simulated cough aerosols between adjacent beds, two common bed layouts in kindergartens were investigated: three beds of staggered height (TBSH) and three beds of uniform height (TBUH). The experiments measured CO₂ and PM_2.5 concentrations (using liquid aerosols generated by an ultrasonic nebulizer as surrogates for cough particles) in the breathing zone of mannequins under different ventilation modes (on and off) and sleeping postures (lying face up and on the right side). The results showed that when ventilation was off, CO₂ concentration near the head of each bed reached nearly 1,000 ppm within 60 min. When ventilation was on, CO₂ concentration was diluted to ambient levels within 3.3 min. However, when the ventilation was on, aerosols exhibited different propagation characteristics compared to CO₂. While CO₂ was rapidly diluted, aerosols accumulated downstream and formed high-concentration zones at adjacent downstream beds. These findings visualize the potential aerosol transmission pathways between beds in kindergarten dormitories and highlight the limitations of using CO₂ as an aerosol transmission tracer. The study found that increasing bed heights along the ventilation airflow direction effectively reduced downstream aerosol concentrations and compensated for the insufficient horizontal distance in kindergarten dormitories. Kindergarten design standards should consider local dilution efficiency in the breathing zone, and bed layouts should be integrated with the ventilation system to ensure air velocities exceed 0.01 m/s near the head, thereby reducing the residence time of pollutants in the breathing zone.