Tier II/Tier III NOx

Tier II and Tier III are NOx emission limits for marine diesel engines under MARPOL Annex VI Regulation 13, set as grams of NOx per kWh on a curve that tightens as rated engine speed falls. Tier II applies worldwide to engines on ships built on or after 1 January 2011 and is about a 20% cut from Tier I. Tier III applies to ships built on or after 1 January 2016 when operating inside a designated NOx Emission Control Area, and is about an 80% cut from Tier I. Tier III usually needs selective catalytic reduction, exhaust gas recirculation, or water injection to meet the limit.