D. Application of Provisions to Marine Diesel Engines Less than 37 kW
Marine diesel engines less than 37 kW were included in the rulemaking for nonroad diesel engines and are subject to the emission control program contained in 40 CFR Part 89. That program has two tiers of emission limits, phased in from 1999 to 2000 for Tier 1 and 2004 to 2005 for Tier 2. In general, marine diesel engines less than 37 kW are subject to the same certification and compliance program as land-based nonroad diesel engines. Exceptions to this general approach include the duty cycle (E3, but with a C1 option), ABT program restrictions (land-based credits cannot be used to offset marine diesel emissions), and implementation flexibility provisions that allow post-manufacture marinizers to phase in compliance with Tier 1 emission limits according to the schedule extended to nonroad equipment manufacturers.
We intend eventually to consolidate the smaller engines in a general marine diesel engine regulation. Consolidating existing requirements without reopening those issues may, however, cause confusion. Commenters did not feel strongly that there would be an advantage to combining programs, so we are not consolidating them at this time. We will likely pursue the next tier of emission standards (i.e., Tier 3) for all marine diesel engines together. This way we will be able to integrate the requirements for varying engines sizes in the most sensible way.
E. Category 3 Engines
State and environmental organization commenters have made clear in their comments that they are eager to see greater emission reductions from Category 3 engines, including PM emissions. These commenters are particularly concerned that the MARPOL NOx limits are not stringent enough to appreciably reduce NOx inventories and ozone levels. Chapter 5 of the Final RIA describes the expected NOx reductions from the MARPOL Annex VI limits in more detail. There is enough foreign vessel traffic in U.S. ports that these engines contribute substantially to local air pollution in port areas. However, imposing separate national requirements on foreign-flagged ships that use U.S. ports raises sensitive concerns relating to international trade and policy. Consequently, we will recommend that the United States urge the International Maritime Organization to consider and adopt more stringent NOx limits as well as PM limits for marine diesel engines. Technologies currently under development for very large marine engines hold a lot of promise for reducing their emissions in the future. The emission standards finalized in this final rule for engines capable of burning heavy fuels (15 L/cyl and larger) also suggest that emission improvements can be obtained from slow- and medium-speed engines. Finally, the standards in this final rule for smaller marine diesel engines will provide a good starting point for a new tier of international standards for those engines.
VII. Projected Impacts
A. Environmental Impacts
Chapter 5 of the Final Regulatory Impact Analysis provides a detailed explanation of the methodology we used to determine the environmental benefits from marine diesel engines associated with this final rule. The following discussion gives a general overview of the methodology and the results.
1. Category 1 Engines
For the purposes of the inventory analysis, Category 1 commercial engines were divided into commercial propulsion and auxiliary categories. Annual emissions were then calculated using engine populations, load factors, annual hours of use, rated power, emission factors, turnover, and growth rates. The sources for and the values of these factors are provided in the Final RIA. Note that we received some indication that the annual use for recreational engines may be lower than assumed in the inventory analysis and calculations (Table 5-2 of the Final Regulatory Impact Analysis).
Table 6 presents the projected emissions inventory from Category 1 commercial propulsion and auxiliary marine engines with and without the new emission standards. Table 6 also presents the anticipated effects of the MARPOL Annex VI standards on the Category 1 NOx inventory. The CO standard places a cap on existing emission levels, so no benefits are claimed here.
TABLE 6.―CATEGORY 1 COMMERCIAL PROPULSION AND AUXILIARY EMISSIONS INVENTORY (THOUSAND SHORT TONS PER YEAR)
2. Category 2 Engines
We developed baseline emission inventories for Category 2 marine engines under contract with Carnegie Mellon University.10 For the purposes of this analysis, emissions are included from all Category 2 engines operated in the Great Lakes, inland waterways, and coastal waters up to 320 kilometers (200 miles) offshore. Emissions from U.S.-flagged vessels were determined using ship registry data, fuel consumption, rated power, operation assumptions, and fuel specific emission factors. Emissions from foreign-flagged vessels were developed based on cargo movements and waterways data, vessel speeds, average dead weight tonnage per ship, and assumed cargo capacity factors.
10 Corbett, J., Fischbeck, P., "Commercial Marine Emissions Inventory and Analysis for United States Continental and Inland Waterways," Carnegie Mellon University, Order No. 8A-0516-NATX, September 1998 (Docket A-97-50; document II-A-01).
To model the benefits of the new standards, we applied an engine replacement schedule and new engine standards to the baseline inventory. In this case, no emission reductions are expected beyond the already low levels of HC. Also, the PM and CO standards are intended as caps, and no benefits are claimed for those pollutants. Table 7 shows the projected emissions for