• Critical transition from density- to turbulence-dominated gas dispersion identified. • Maximum gas dispersion deviation drops from 10.42% to <1% beyond critical Re. • Particle deposition shifts from near-source to downwind inertial impaction with Re . • Rooftop PV soiling risk concentrates at windward building edges. The fugitive emissions from urban industrial buildings pose significant environmental and health risks and also constrain the performance of building-integrated photovoltaic systems. This study quantitatively reveals the dispersion and deposition of fugitive industrial gases and particles within industrial areas and adjacent residential areas through numerical simulations. The results indicate that the dispersion distance of gaseous pollutants is primarily determined by the flow regime transitions driven by the Reynolds number ( Re ). At Re ≤ 2 . 5 × 1 0 4 , gas dispersion is influenced by density differences, with high-density gases migrating farther downstream. At Re ≥ 5 . 1 × 1 0 4 , inertial effects reduce this influence, leading to a more confined and convergent dispersion pattern (relative deviation < 1%). Particle deposition shows spatial variations in deposition. Within the industrial area, street-canyon ground strongly retains large particles (40–50 μm) under low- Re conditions ( Re = 1 . 2 × 1 0 4 ), yielding a deposition rate of 16.39%. The critical particle sizes for rooftop deposition increase from 20 μm to 30 μm with increasing Re . In residential areas, particles on rooftops and building facades exhibit a characteristic enrichment along the upwind edges, while ground-level deposition extends farther downstream as Re increases. Elevated deposition rates of coarse particles on street-canyon ground indicate heightened health risks for ground-level occupants. Meanwhile, localized rooftop deposition, particularly the edge-accumulation phenomenon, poses potential threats to photovoltaic module performance. This study elucidates the critical transition mechanisms of pollutant dispersion and deposition, and quantitatively characterizes their risk distribution in the built environment.
Cao et al. (Fri,) studied this question.