7 Finally, there is growing concern that ship emissions of NOx and HC may be associated with global climate change. Although these pollutants are not among the direct greenhouse gases of primary concern to the United Nations Framework Convention on Climate Change (UNFCCC), NOx is an ozone precursor that may interact with hydrocarbons (HC) to increase the production of ozone, which is a greenhouse gas. While the contribution of ships to global HC emissions is much lower than other pollutants, some researchers have suggested that the effect of these HC emissions may be notable, particularly in the remote ocean where significant NOx emissions from ships make ozone production "HC limited" (i.e., the amount of HC emitted may effectively cap the potential for ozone formation in remote locations). Research is currently underway to better define how tropospheric ozone formation may contribute to global warming and how ship-generated NOx, as well as HC, emissions may affect this scenario.
Inventory impacts of marine diesel engines and expected regulation 13 NOx reductions
8 At the time the Regulation 13 emission limits were drafted, NOx emissions from marine diesel engines were not well understood and the international community had actual emissions data from only a very few engines on which to base the standards. Since that time, more engine emission data has become available for all sizes of marine diesel engines, including a test program carried out by Lloyds Register, as well as various marine engine manufacturers. 1
9 Some studies estimate the total contribution of marine diesel engines to NOx inventories at 4 percent or higher. A recent study by Corbett and Fischbeck estimates that these engines may contribute as much as 14 percent of world-wide nitrogen emissions from fossil fuels annually.2 This is as much as 42 percent of the annual NOx emissions of North America, 50 percent of the annual NOx emissions of the United States, and 74 percent of the annual NOx emissions of OECD Europe. As illustrated in Table 1, below, the majority of these emissions, approximately 64 percent, are from bulk cargo and general cargo ships.
1J. S. Carlton, et al., Marine Exhaust Emissions research Program. Lloyds Register Engineering Services, London, 1995; Marine Exhaust Emissions Research Programme: Steady State Operation including Slow Speed Addendum. Lloyds Register of Shipping, London, 1990.
2J.J. Corbett and P. Fischbeck, "Emissions from Ships." Science, Volume 278, pages. 823-825 (1997).
