The Environmental Protection Agency (EPA) participates on the U.S. delegation to the International Maritime Organization (IMO), which is part of the United Nations. The Marine Environment Protection Committee (MEPC) is a group of member states within IMO that works on maritime safety and security and the prevention of marine pollution. The resulting global standards are embodied in the International Convention on the Prevention of Pollution from Ships, a treaty called "MARPOL." In particular, MARPOL Annex VI defines engine and vessel requirements related to air pollution.
The first round of standards under MARPOL Annex VI, adopted in 1997 and entered into force in 2005, involved maximum allowable sulfur concentrations in marine fuels, and maximum oxides of nitrogen (NOx) emission rates in engine exhaust. MARPOL Annex VI was amended in 2008, most importantly to set more stringent fuel sulfur limits and more stringent NOx emission standards, especially for vessel operation in designated Emission Control Areas (ECAs).
Per the EPA report:
Together with Canada and France, the U.S. Government successfully petitioned the International Maritime Organization to designate the North American Emission Control Area for both fuel-sulfur standards and NOx emission standards. This area includes most coastal waters up to 200 nautical miles from the coasts of the continental United States and large portions of coastal waters around Alaska and Hawaii, in addition to significant portions of the Canadian coasts and the French Islands of Saint Pierre and Miquelon.
The U.S. Government later successfully petitioned the International Maritime Organization to also designate the U.S. Caribbean Sea Emission Control Area for both fuel-sulfur limits and NOx emission standards. This area includes waters surrounding Puerto Rico and the U.S. Virgin Islands.
- Fuel-sulfur concentrations may not exceed 0.10 weight percent, or vessels may use an approved equivalent method (such as SOx scrubbers, also known as exhaust gas cleaning systems).
- Engines above 130 kW installed on vessels built (or modified) since 2000 must be certified to meet appropriate emission standards corresponding to the vessel's build date (or modification date). As of January 1, 2016, engines installed on new and modified vessels are subject to the Annex VI Tier III NOx standards while those engines are operating in the ECA.