6 December 1999

The US EPA signed the final rule regulating emissions from new marine diesel engines of above 37 kW (50 hp). This rulemaking follows a proposed rule published in December 1998. The final rule includes several changes from the earlier proposal that were suggested during the public discussion process.

The adopted standards for small- and medium-size marine engines, up to 30 liters displacement per cylinder, are based on the land-based standard for nonroad engines, while the largest engines are expected (but not required by the EPA) to comply with the MARPOL Annex VI limits. The regulation sets emission limits for NOx+THC, PM, and CO. Numerical values of the limits are listed in the US marine engine emission standards page.

The regulation will be implemented between 2004 and 2007, depending on the engine category. It applies for engines that are used for propulsion and auxiliary power on commercial vessels in a variety of marine applications, including fishing boats, tug and towboats, dredgers, coastal and Great Lakes cargo vessels, and ocean-going vessels. They also apply to drill rigs with propulsion capabilities, while stationary drilling facilities remain regulated by land-based nonroad engines regulations.

Auxiliary engines covered by the marine rule are defined as those that are installed on a marine vessel, i.e., if their fuel, cooling, or exhaust system are an integral part of the vessel or require special mounting hardware. All other auxiliary engines are considered to be portable and therefore subject to the existing land-based nonroad engine emission regulation.

Major exemptions from the marine rule include engines used in recreational vessels (which will be subject to a separate regulation at a later time), engines used for the purpose of national security (such as military vessels), and competition (i.e., racing) engines.

Standards adopted by the final rule are somewhat relaxed compared to the EPA proposal of December 1998. For example, while the proposed NOx+HC standard for all regulated engines was 7.2 g/kWh, the final regulation adopts standards between 7.2 and 11.0 g/kWh, depending on the engine size. PM standards and implementation dates have also been relaxed for some engine categories. The proposal called for a more stringent Tier 3 standard to be implemented between 2008 and 2010, which has not been adopted in the final rule. EPA, however, said it would issue the Tier 3 marine standard in a separate rulemaking.

Emissions from the largest ocean-going ships with engines of above 30 liters per cylinder were left unregulated. These engines are covered by the International Maritime Organization (IMO) MARPOL Annex VI NOx limits. The Annex VI is not yet in force, pending ratification by a number of member states, including the USA Once adopted, the Annex VI limits will apply retroactively, effective 1 January 2000. Therefore, ocean vessel operators worldwide are expected to install complying engines starting in the year 2000. Some marine engine manufacturers (see Caterpillar) already announced introducing MARPOL Annex VI compliant diesel engines.

The EPA also stated that if manufacturers continue to sell engines with emissions above MARPOL levels or if the Annex VI is not ratified by the United States or does not go into effect internationally, the need to adopt emission limits for the largest ships under the Clean Air Act will be revisited.

According to the EPA, emissions from marine diesel engines account for about 4.4% of total mobile source NOx emissions nationwide and about 1% of PM emissions. The final marine engine rule is expected to lead to a 24% reduction in NOx emissions and a 12% reduction in PM emissions in 2030 when the program is fully phased-in. These emission reductions will be especially important in the areas around commercial ports and heavily populated coasts.

Until now, marine engines emissions remained unregulated. With the adoption of this rule, emissions from all categories of diesel engines, with only a few minor exceptions, are regulated in the USA.