Unveiling infrastructure-induced vertical environmental inequity near elevated roads via drone-based measurements

Elevated roads can alter near-road airflow and redistribute traffic-related air pollution vertically, creating height-dependent exposure for residents in adjacent high-rise buildings. In this study, drone-based vertical profiling was conducted in Fuzhou, China, yielding over 100,000 valid 10-second measurements of PM_1.0, PM_2.5, and black carbon (BC) concentrations along an elevated roadway, together with concurrent microclimate observations across 0-200 m altitude. Following calibration against regulatory-grade reference instruments, the height-resolved dataset was integrated into an inhalation-pathway health risk framework to derive outdoor, height-stratified exposure metrics. Compared with at-grade road sections, elevated-road sites exhibited non-monotonic vertical pollution structures consistent with a lid effect, characterized by enhanced retention within 0-20 m and higher concentrations on the densely built leeward side; vertical gradients were generally stronger in winter than in summer. Under the conventional EPA's inhalation risk assessment framework for site-specific pollutants, PM_2.5 posed a substantial non-carcinogenic risk in winter: children's hazard quotient (HQ) exceeded 1 across all height layers, while adults' HQ surpassed 1 mainly at upper residential heights (∼100-120 m). For BC, HQ remained below 1, whereas the estimated lifetime cancer risk ranged from 10^-6 to 10^-4 (moderate risk), indicating non-negligible long-term risk in specific vertical zones. Incorporating temperature-dependent ventilation further modified height- and season-specific patterns, amplifying winter risk indicators at upper residential heights and demonstrating that reliance on ground-level concentrations and constant inhalation rates may underestimate winter exposure potential at these elevations. These findings support height-aware assessment and mitigation strategies for elevated-road corridors, including improved under-bridge ventilation and height-stratified exposure management for nearby high-rise residences.