Route level and mode resolved emission dispersion analysis of tugboat operations along offshore terminal routes: implications for coastal air quality

Abstract

This study investigates the potential coastal air quality implications of tugboat operations associated with offshore mooring-buoy routes in Trabzon Port (Black Sea, Türkiye) through a route-level and mode-resolved integrated assessment combining an activity-based emission inventory, AERMOD dispersion modeling, and non-parametric statistical analysis. Harbor craft operating within port basins represent a localized yet influential emission source that may affect both coastal urban air quality and adjacent marine environments. Emissions of NOx, CO, SO 2 , PM, and HC were estimated for two operational routes under cruising and maneuvering modes using a Tier-3 time-in-mode methodology. Annual emissions associated with the shared Route B corridor reached 6.54 t NOx and 2.62 t CO, approximately 18% higher than the corresponding Route C totals. This difference reflects the route-accounting structure because the Port–B segment is traversed by both B-bound operations and C-bound operations continuing toward the more distant offshore terminal. Receptor-based analysis showed that offshore concentrations exceeded land concentrations for both routes, with a stronger offshore-to-land contrast along Route C. Statistical analyses confirmed significant differences between routes (p < 0.05) and highlighted autumn as the most critical period. Overall, the findings emphasize the importance of jointly evaluating emission totals and modeled dispersion patterns when assessing potential air quality relevance. This study provides a route-level and mode-resolved framework for evaluating tugboat emissions associated with offshore terminal routes and enables the development of spatially targeted mitigation strategies for supporting coastal air quality management in port environments.