10 While the contribution of marine diesel engines to world-wide NOx levels has been estimated at 4 to 14 percent, it is important to note that a disproportionate share of these emissions may occur along coastlines and in commercial ports, many of which are located in highly populated, industrial settings and many of which are already experiencing serious air pollution. Corbett estimates that approximately 70 percent of these emissions occur within 400 kilometers from shore. Depending on prevailing traffic and wind patterns, and other variables, these emissions can have an important effect on land-side ozone levels.
11 Because the Annex VI NOx limits are so close to average uncontrolled emission levels, the contribution of these engines to NOx inventories is not expected to be greatly reduced. For example, using available domestic data, US EPA estimated the expected reductions from the Regulation 13 emission limits for the U.S. domestic marine diesel NOx inventory, assuming the Regulation 13 standards are implemented as planned beginning 1 January 2000.3 These results, set out in Table 2, indicate that the Regulation 13 emission limits are expected to result in only a 6 percent reduction in marine diesel NOx emissions in the United States by 2020, and increasing to 7 percent by 2030. Again, while these estimates are only for the United States, they suggest the modest NOx reductions that can be expected world-wide from the current standards.
When only propulsion systems on very large ocean-going vessels are considered, the Regulation 13 emission limits are expected to achieve a somewhat higher reduction in marine diesel NOx emissions. For example, US EPA estimated the marine diesel NOx reductions from large marine diesel engines (those above 30 l/cyl displacement) at 13.5 percent in 2020 (see Table 3). These estimates are based on the assumption that the Regulation 13 emission limits are phased in as planned, beginning 1 January 2000.
3Final Regulatory Impact Analysis: Control of Emissions from Marine Diesel Engines. United States Environmental Protection Agency, Office of Air and Radiation, Office of Mobile Sources, Engine Programs and Compliance Division, November 1999.
