4 December 2007

The US Environmental Protection Agency (EPA) has issued an Advance Notice of Proposed Rulemaking (ANPR) which outlines the agency’s plan to propose new emission standards for new Category 3 (≥ 30 liters per-cylinder displacement) marine diesel engines. Such engines are typically used in large oceangoing vessels.

In January 2003, the EPA adopted Tier 1 emission standards for new Category 3 engines, which are equivalent to the internationally negotiated International Maritime Organization (IMO) MARPOL Annex VI limits for NOx emissions. The MARPOL Annex VI standards, considered rather relaxed, range from NOx = 9.8 to 17 g/kWh depending on the engine speed, with higher limits for slower engines. They can be met by in-cylinder control methods.

The EPA is conducting the rulemaking process simultaneously with negotiations for a new tier of international marine diesel engine standards. The emission standards discussed in the ANPR are based on a proposal submitted by the US EPA to the 11th meeting of the IMO Subcommittee on Bulk Liquids and Gases, held in April 2007. The standards under consideration consist of two tiers of NOx emission standards and performance-based SOx and PM standards:

  • Tier 2 NOx standards, which could begin as early as 2011, would achieve a 15 to 25% NOx reduction below the current Tier 1 emission levels. These standards would be met through optimized in-cylinder controls.
  • Tier 3 NOx standards, which could begin as early as 2016 and would apply while ships are operated in specially designated areas, would reduce NOx 80% below the Tier 2 standards. These standards could be met by using SCR catalysts or water injection technologies.
  • Performance-based SOx and PM standards would also apply while ships are operating in those special areas and could begin as early as 2011. These performance-based standards could be met through the use of low-sulfur distillate fuel, on the order of 1,000 ppm, or through the use of exhaust aftertreatment technologies such as SOx scrubbers.

The program also contains NOx limits that would apply to engines on existing vessels that would reduce their emissions by 15 to 20%.

Category 3 engines provide a substantial contribution to air pollution, which is expected to grow in the future. Based on EPA’s new emission inventory analysis, these engines contributed nearly 6% of mobile-source NOx, more than 10% of mobile-source PM2.5, and about 40% of mobile-source SO2 in 2001. These contributions are predicted to increase to about 34% of mobile-source NOx, 45% of mobile-source PM2.5, and 94% of mobile-source SO2 by 2030 without further controls on these engines.

The EPA was originally under obligation to finalize the Tier 2 emission standards for Category 3 engines by April 2007, but it delayed the deadline to December 17, 2009. This triggered a lawsuit by the Friends of the Earth environmental group.

The EPA will accept public comments on the ANPR until February 29, 2008.

Source: US EPA