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US EPA proposes emission standards for large marine diesel engines

7 May 2002

On 30 April 2002, the US Environmental Protection Agency (EPA) signed proposed emission standards for large marine diesel engines. The proposal affects “Category 3” engines of over 30 liters of displacement per cylinder, such as those used for propulsion power on oceangoing container ships, tankers, bulk carriers, and cruise ships.

In 1999, the EPA adopted emission standards for new commercial marine diesel engines. The largest “Category 3” engines, however, were left unregulated in an expectation that they would comply with the internationally negotiated MARPOL Annex VI limits for nitrogen oxides (NOx) emissions, as adopted by the International Maritime Organization (IMO). This triggered a law suit against the EPA by an environmental organization called the “Earth Island Institute”. Eventually a court settlement was reached which required the EPA to propose NOx emission limits for Category 3 engines no later than 30 April 2002. The court settlement did not specify the stringency of the limits, which was up to the EPA to decide.

Three sets of standards are considered by the proposal: (1) first tier standards, (2) second tier standards, and (3) voluntary low-emission engine standards. The first tier standards would be equivalent to the internationally negotiated NOx limits (the MARPOL Annex VI limits vary from 9.8 to 17 g/kWh NOx, depending on the engine speed). They would be enforceable under US law for new engines built in 2004 and later. These limits would be achieved by engine-based controls, without the need for exhaust gas aftertreatment. A subsequent second tier of standards, which would reflect additional reductions that can be achieved through engine-based controls, would apply to new engines built after 2006 or later. The voluntary low-emission engine standards reflect advanced NOx emission control technologies. Meeting these standards would likely require the use of technologies such as selective catalyst reduction, water-based emission reduction techniques, or fuel cells.

According to EPA estimates, emissions from all marine diesel engines at or above 30 liters per cylinder, regardless of flag of registry, currently account for about 1.5% of US national mobile source NOx emissions. This contribution can be significantly higher on a port-specific basis (5 to 25% of mobile source emissions in certain key ports by the year 2020). The proposed NOx standards, which would apply only to new engines on US flag vessels, are expected to reduce these national emissions by about 11% by 2030. The contribution of these engines to national mobile source hydrocarbon (HC) and carbon monoxide (CO) inventories is small (< 0.1%). The EPA is considering HC and CO standards to ensure that these emissions do not increase on a engine-specific basis.

The contribution of these engines to the national mobile source particulate matter inventory is about 2.6%. Reductions in particulate emissions could be obtained from setting a sulfur content standard for the fuels that are used by these engines. EPA estimates that fuels used today in oceangoing vessels have sulfur content up to 45,000 ppm (4.5%); the global average sulfur concentration is currently about 27,000 ppm, though fuel sold in the US has sulfur levels somewhat above the average. Operating on fuels with such high sulfur contents results in high SOx and direct sulfate PM emissions. The EPA requested comment on whether fuel standards should be adopted and, if so, what level of sulfur should be allowed.

The EPA also proposed proposing new requirements for engines at or above 2.5 liters per cylinder but less than 30 liters per cylinder. The Tier 2 standards finalized for these engines in the 1999 marine diesel engine rule apply beginning in 2007. Under the proposal, engine manufacturers would be required to certify these engines to the Tier 1 standards, starting in 2004.

The proposed standards would apply to engines installed on vessels flagged in the USA. The EPA has requested comment on whether the proposed standards and existing Category 1 and Category 2 standards should also apply to marine engines on foreign vessels entering US ports. It is currently not clear if the US government has the authority to impose such standards for foreign ships, which present the vast majority of vessels entering US ports.

The proposal was severely criticized by the environmental lobby for its very limited emission reduction targets. In particular, the Tier 1 standards bring almost no environmental benefit. The MARPOL Annex VI limits, which must be considered relaxed, are already met by most currently built marine engines. The proposal was praised by the ship industry who lobbied against adopting US standards that would be more stringent than those outlined in the international agreements.

The final rule is due by 31 January 2003. The EPA will hold a public hearing on 13 June 2002 in Long Beach, CA. Written comments on the proposed rule will be accepted by 16 July 2002. Contact: Margaret Borushko, EPA, (734) 214-4334; borushko.margaret@epa.gov.

Download the proposal

Source: EPA