Experimental investigation of vessel emission dispersion and exposure levels

Pollutant dispersion from vessel emissions is investigated in an atmospheric boundary layer wind tunnel using a generic geometry representative of an offshore service vessel. The vessel model is exposed to neutral maritime flow conditions and densimetric Froude number similarity to the real-world configuration is enforced to realistically replicate buoyancy-driven plume dynamics. Time-averaged concentration levels are assessed at 1.5 m above deck for three wind directions, i.e., γ = 0° (headwind) and γ = ±15°, two Maximum Continuous Rating (MCR) engine loads (25% and 75%), and two approach flow velocities (10 m/s and 20 m/s at exhaust height). An analytical framework is proposed to relate measured concentration fields to potential exposure levels. Long-term and short-term exposure levels are investigated for the most critical wind direction (γ = −15°). Results demonstrate that deck-level exposure is governed by the interaction between buoyant plume dynamics, vessel-induced wake structures, and exhaust momentum. For γ = 0° and −15°, plume–wake interaction causes pollutant trapping and elevated deck-level concentrations, whereas for γ = 15° exhaust momentum and wind direction transport pollutants away from the vessel. Increasing engine load enhances exhaust momentum, enabling the plume to escape recirculation regions and reducing on-deck concentrations. It is further shown that hazardous gas exposure can exceed occupational limits, but exhaust gas after-treatment systems and low-sulfur fuel effectively reduce exposures, enhancing occupational safety and mitigating potential health impacts on deck. Overall, this work shows that controlled wind-tunnel measurements combined with exposure-oriented analysis can translate vessel-scale dispersion behavior into safety-relevant metrics.