Dynamic wind patterns and indoor/outdoor pollutant dispersion in the simplified building array: Statistical and spectral analyses from scaled outdoor experiments

Abstract

In real urban environments, dynamic changes in wind significantly influence the pollutant dispersion within building complexes. To investigate the impact of urban-like wind conditions on the pollutant transmission, this study conducted a scaled outdoor experiment using a three-dimensional (3D) 3×3 building array model in a sub-urban area of Guangzhou, with a humid subtropical climate. Tracer gas (CO₂) was continuously released to simulate the pollutant dispersion in the indoor and outdoor environment within the array. Wind speed, wind direction, and tracer gas concentrations were monitored simultaneously. Both statistical and spectral analyses were employed to evaluate the dynamic variation characteristics of the wind, while the air change rate (ACH) and reentry ratio $\left(R_k\right)$ were used to assess ventilation performance and pollutant dispersion. Based on the real-time wind conditions, the results indicated that the standard deviation (SD) of wind direction within the building arrays were higher than those in open areas, while the velocity power spectrum exponent (${\beta }_v$) was lower, below 1.1, suggesting intense high-frequency fluctuations. Wavelet coherence (WTC) analysis indicates significant correlations between the variations in airflow and pollutant concentration, particularly in the vertical direction. The results of tracer gas concentrations demonstrated that the dynamic airflow influenced the dispersion pathways over time. Airflow within the building arrays exhibited a strong capacity for dispersing pollutants, with the average $R_k$ for all units being below 4 %. This study provides realistic, transient insights into winds effects on pollutant dispersion within the building arrays, and the generated dataset offers a validation benchmark for future numerical simulations.