Indoor particle dynamics in schools: Determination of air exchange rate,size-resolved particle deposition rate and penetration factor in real-life conditions

Abstract

Indoor and outdoor airborne particles, CO, CO₂ levels and comfort parameters were monitored at two naturally ventilated elementary schools (S1 and S2). This paper studies the variation of ventilation rate during lectures, recreations, lunchtime and after class. Additionally, mass balance equations were used to estimate the particle deposition rates and penetration factors for different particle size fractions. The originality of the present work resides in taking advantage of occupants’ activities as sources of indoor particles and tracer gas CO₂ used to simultaneously estimate the above-mentioned parameters in different scenarios. This simple approach makes the determination of indoor particle dynamics more effective, and allows reducing the cost of indoor air quality studies. During the class, the ventilation rates at S1 and S2 fluctuated largely from day to day, with respective average values of 10.08 m³/h/p and 7.92 m³/h/p, significantly lower than the ASHRAE acceptable value (18 m³/h/p) in classrooms. The particle deposition loss rate coefficients for 0.3–10 µm particles dramatically increased from 0.16–0.18 h⁻¹ for the 0.3–0.5 µm fraction to 1.81–2.31 h⁻¹ for the 7.5–10 µm fraction, while their corresponding penetration factors declined from 0.94 to 0.30, respectively. The difference in deposition rate between schools was probably associated to discrepancies in particle density.