Experimental study of environmental factors affecting particle infiltration in buildings

Ambient particles infiltrate indoor environments through cracks in the building envelope, deteriorating indoor air quality and posing risks to human health. This study investigates the factors influencing particle infiltration in controlled laboratory settings, utilizing an orthogonal experimental design. The effects of outdoor particle concentration (C_out), crack structure factor (q), indoor temperature (T_in), and indoor relative humidity (RH_in) on indoor particle concentration (C_in) and infiltration factor (F_inf) are quantified using multivariate regression analysis. Particle mass and number concentrations were measured in sixteen experimental scenarios to characterize infiltration behavior and particle size distribution. Results demonstrate that C_in increases predominantly with C_out, such that a 1 μg m⁻³ increase in C_out leads to a 0.382 μg m⁻³ increase in C_in, assuming all other factors remain constant. Regression modeling identifies optimal conditions for C_in at C_out = 50 μg m⁻³, RH_in = 30 %, and U-shaped cracks. Meanwhile, F_inf rises with q and RH_in but decreases with increasing T_in, achieving its minimum at RH_in = 30 %, T_in = 30 °C, and U-shaped cracks. Size-resolved analysis shows infiltration peaks for 0.4–0.5 μm particles at RH_in = 90 %, suggesting that particles smaller than 0.5 μm undergo hygroscopic growth and coagulate into this range. By incorporating temperature and humidity variables, this study establishes predictive models for particle infiltration, providing actionable strategies for optimizing indoor air quality management while balancing energy efficiency. These findings advance the understanding of particle infiltration in buildings and inform the formulation of targeted design codes.