Assessing the Environmental Impact of Exhaust Gas Cleaning System (EGCS) Discharges from Seagoing Ships

Following the new limits on the sulfur content in fuel oil and reduction of air emissions of sulfur oxide (SOx) set forth by the 2020 Sulfur Cap, open-loop EGCSs are being installed onboard vessels to achieve regulatory compliance. The open-loop EGCS redirects sulfur oxides and other constituents in engine exhaust gas into the ocean, thus triggering investigations of the potential risk of ECGS effluent to the marine environment. This study presents two stochastic models (near-field and far-field) to compute the dilution and mixing of the effluent at different spatial scales (e.g., open seas, harbors). The near-field model computes the 3D, steady-state concentration distribution resulting from the EGCS effluent discharged by a fleet of ships in busy open waters such as straits and canals. The far-field model addresses the cumulative equilibrium wash water concentration in enclosed waterbodies such as bays and ports, where background build-up of effluent due to poor flushing (water exchange) could be significant. The models are applied to key global shipping routes to assess impacts on these regions.