Amendments to MARPOL Annex VI (regulations for the prevention of air pollution from ships) to establish the North American ECA entered into force on 1 August 2011, with a 12-month period before becoming effective.

There are now three designated ECAs in effect globally, the other two being sulphur-oxide ECAs in the Baltic Sea area and the North Sea area.

A fourth area, the United States Caribbean Sea ECA, covering certain waters adjacent to the coasts of Puerto Rico and the United States Virgin Islands, was designated under MARPOL amendments adopted in July 2011, with expected entry into force on Jan. 1, 2013, with the new ECA to take effect 12 months later on Jan. 1, 2014.

In practice, within an ECA ships must burn fuel oil of a lower sulphur-oxide content. Alternatively, the ship may use any "fitting, material, appliance or apparatus or other procedures, alternative fuel oils, or compliance methods," which are at least as effective in terms of emissions reductions, as approved by MARPOL.

With regard to nitrogen-oxide emissions, marine diesel engines installed on a ship constructed on or after Jan. 1, 2011, must comply with the "Tier II" standard set out in regulation 13 of MARPOL Annex VI. Marine diesel engines installed on a ship constructed on or after Jan. 1, 2016, will be required to comply with the more stringent Tier III nitrogen-oxide standard, when operated in a designated nitrogen-oxide ECA.

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