HomeCalculatorsNOₓ Tier I / II / III Limits

NOₓ Tier I / II / III Limits

Maximum permitted NOₓ emissions per MARPOL Annex VI Regulation 13 and the IMO NOx Technical Code. Tier depends on the engine's construction date; Tier III applies only in NECAs.

PollutantsMARPOL VI Reg 13

Rated engine speedrpmTierEngine power (for mass estimate)kWAnnual operating hoursh

NOₓ limit

14.40g/kWh

Tier II limit at 100 rpm.

Maximum annual NOₓ at limit

691.2t

NOₓ limits from MARPOL Annex VI Reg 13

Tier I:  17.0 (rpm<130), 45·n^(-0.2) (130≤rpm<2000), 9.8 (rpm≥2000)
Tier II: 14.4 (rpm<130), 44·n^(-0.23)(130≤rpm<2000), 7.7 (rpm≥2000)
Tier III: 3.4 (rpm<130), 9·n^(-0.2) (130≤rpm<2000), 2.0 (rpm≥2000)

Tier I - ships built 1 Jan 2000 to 31 Dec 2010.
Tier II - ships built ≥ 1 Jan 2011 (global).
Tier III - ships built ≥ 1 Jan 2016 operating in NOx Emission Control Areas (North America, US Caribbean from 2016; Baltic + North Sea from 2021).

Tier III outside NECAs can operate under Tier II. SCR or EGR equipment is typically needed for Tier III compliance.

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