River Geomorphology Shapes the Pollution Intensity and Chemical Fingerprints of Inland Shipping VOC Emissions

Inland shipping is a critical source of volatile organic compounds (VOCs), but emission inventories rely on spatially averaged load factors that fail to capture localized transient events. We addressed this gap through an 800-km high-frequency mobile measurement campaign along the Yangtze River. The observations revealed a striking spatial anomaly: the most intense pollution hotspots (>50 ppbV) were spatially decoupled from the high-traffic Wuhan megacity, clustering instead within the remote, sinuous Jingjiang channel. Chemical forensics explicitly ruled out topographical trapping. Unlike steady cruising plumes, these hotspots exhibited exceptionally high toluene-to-benzene ratios (∼13.0) and enriched unburned fuel tracers. High-frequency GPS tracking confirmed that this distinct fingerprint is driven by a 4.2-fold increase in vessel speed fluctuation variance, proving that hydrodynamic resistance in tortuous channels compels vessels into inefficient transient combustion regimes. We conclude that navigational complexity acts as an invisible stressor creating localized pollution risks evaded by regional traffic-based models.