The Ship Emissions Assessment (SEA) produced the first geographically resolved, global inventory of emissions from commercial ship engines operating internationally. This inventory shows that ship engine combustion is an important source for several air pollutants, including oxides of nitrogen (NOx), and oxides of sulfur (SOx). For example, we estimated annual NOx and SOx emissions from ships to be 3.08 Tg (1012 grams) as N, and 4.24 Tg as S, respectively [Corbett and Fischbeck, 1997; Corbett et al., 1998b]. In other words, international ship emissions represent more than 14 percent of nitrogen emissions from global fuel combustion sources and more than 16 percent of sulfur emissions from world petroleum use [Corbett and Fischbeck, 1997]. Using the SEA inventory, we showed that nearly 70% of ship emissions occur within 400 km of land regions, that 85% occur north of the equator, and that ship air pollution can be of regional importance where they may be of the same order or greater than adjacent land-based emissions. We also showed that globally ship sulfur emissions equal about 20-25% of the global ocean dimethylsulfide (DMS) emissions, but can equal or exceed DMS flux in the mid-latitudes of the Northern Hemisphere and other regions where shipping is intense[Corbett et al., 1998b]. By including our work in global chemical transport models, we showed that sulfur emissions from ships account for 70-100% of the SO2 concentration and 10-30% of the SO4 concentration in the remote marine boundary layer [Capaldo et al., in preparation; Corbett et al., 1998a]. Near land regions, our model predictions showed that ship emissions contribute 5-30% to the ambient sulfur concentrations near many populated land regions [Capaldo et al., in preparation]. (Similar global modeling analyses are underway to quantify the contribution of nitrogen emissions to NOx and ozone concentrations in both remote ocean and coastal regions.) Other air pollutants and carbon dioxide were estimated in the SEA, which has contributed to the fundamental understanding of the remote ocean atmosphere, and to the applied science of regional air pollution.

On a regional level, our research also produced the first comprehensive national inventory of commercial ship emissions for the United States [Corbett and Fischbeck, 1998a; Corbett and Fischbeck, in preparation], improving upon earlier attempts [Davis, 1995; EPA, 1991]. By combining an engineering analysis of ship engine operations with trade data describing the tons of cargo moved over the nation's navigable waterways, we estimated ship emissions in U.S. waters to be more than three times as great as earlier calculations. For example, our estimates for NOx emissions from ships (foreign and domestic) in U.S. waters is 747 thousand metric tons [Corbett and Fischbeck, 1998a; Corbett and Fischbeck, in preparation], compared to the 236 thousand metric tons reported in the Transportation Energy Data Book: Edition 15 [Davis, 1995]. Moreover, our results indicate that emissions from ships on U.S. inland rivers equal about 70% of the emissions from ships on all three U.S. coastlines combined ­ despite the fact that three times as many miles of the U.S. navigable waterways extend along coastal borders [Corbett and Fischbeck, 1998a]. Because of this work, ship emissions in U.S. waters can be more accurately included in nationwide and regional air quality studies.
However, our research is not limited to the assessment of ship air emissions and their impacts. We also address some of the alternatives to reduce these emissions. We examine various NOx control strategies, including engineering alternatives and policy options, to develop a current feasibility assessment that ranks these strategies according to a weighted-combination of multiple criteria (to be completed by February 1999). These rankings will be tailored to three different potential policy scenarios: 1) Control of emissions during 100% of vessel operation; 2) Control of emissions when ships are considered within range of pollution transport; and 3) Harbor/port area control within some legal boundary of jurisdiction. Additionally, our research considers the environmental implications regulatory and/or economic changes that may result in a modal shift of cargo transport between ship, rail, and truck.