Benefits of Two Mitigation Strategies for Container Vessels: Cleaner Engines and Cleaner Fuels

Emissions from ocean-going vessels (OGVs) are a significant health concern for people near port communities. This paper reports the emission benefits for two mitigation strategies, cleaner engines and cleaner fuels, for a 2010 container vessel. In-use emissions were measured following International Organization for Standardization (ISO) protocols. The overall in-use nitrogen oxide (NOx) emission factor was 16.1 +/- 0.1 gkW(-1) h(-1), lower than the Tier 1 certification (17 gkW(-1) h(-1)) and significantly lower than the benchmark value of 18.7 gkW(-1) h(-1) commonly used for estimating emission inventories. The in-use particulate matter (PM2.5) emission was 1.42 +/- 0.04 gkW(-1) h(-1) for heavy fuel oil (HFO) containing 2.51 wt % sulfur. Unimodal (similar to 30 nm) and bimodal (similar to 35 nm; similar to 75 nm) particle number size distributions (NSDs) were observed when the vessel operated on marine gas oil (MGO) and HFO, respectively. First-time emission measurements during fuel switching (required 24 nautical miles from coastline) showed that concentrations of sulfur dioxide (SO2) and particle NSD took similar to 55 min to reach steady-state when switching from MGO to HFO and similar to 84 min in the opposite direction. Therefore, if OGVs commence fuel change at the regulated boundary, then vessels can travel up to 90% of the distance to the port before steady-state values are re-established. The transient behavior follows a classic, nonlinear mixing function driven by the amount of fuel in day tank and the fuel consumption rate. Hence, to achieve the maximum benefits from a fuel change regulation, fuel switch boundary should be further increased to provide the intended benefits for the people living near the ports.