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

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This calculator requires JavaScript to compute its result. The formula, symbols, and regulatory sources are shown in the Formula section below.

Formula, assumptions, and limits

L^{(I)}(n) = \begin{cases} 17.0 \& n < 130 \ 45 n^{-0.2} \& 130 \le n < 2000 \ 9.8 \& n \ge 2000 \end{cases}

Symbol	Meaning	Unit
$L^{(t)}$	Maximum NOₓ rate at tier $t$	g/kWh
$n$	Rated engine speed	rpm

Source: MARPOL Annex VI Regulation 13; IMO NOx Technical Code 2008 (MEPC.177(58))

In short

Look up NOₓ emission limits per MARPOL Annex VI Reg 13 based on engine speed and certification tier, plus annual-mass estimate.

Learn the theory Engine Performance Monitoring: PMI Systems