Mitigating traffic pollution alongside elevated roads: Insights into vertical emission transmissions

Elevated roads heighten traffic emissions and alter airflow patterns, posing unresolved questions regarding their impact on roadside air pollution compared to flat roads. This study utilized drone-based monitoring and machine learning to analyze vertical traffic pollution levels to inform elevated road design. Results revealed that roads elevated about 8 m above ground significantly raised black carbon (BC) levels, strongly associated with diesel vehicle emissions, at heights of 20–40 m. Under-bridge closures caused notable changes in all particle types, including PM_2.5 and PM_1.0, up to heights of 60 m. Elevated traffic emissions also intensified ozone (O₃) vertical gradients. The resilient random forest model further found strong correlations between particle vertical structures and boundary layer height, alongside significant relationships with local temperature, humidity, and solar radiation. Pollution mechanisms varied within 0–20 m compared to higher elevations, particularly extending to 40 m for BC near the closed under-bridge road, suggesting the necessity for tailored control measures.