Regulation 13 of MARPOL Annex VI limits NOx emissions from marine diesel engines. The limits (g/kWh) for the different Tiers are a function of the engine rated speed n (rpm):

• For n < 130 rpm (slow-speed engines): Tier I = 17.0, Tier II = 14.4, Tier III = 3.4 g/kWh.
• For 130 to < 2000 rpm: the limit is interpolated logarithmically; at 130 rpm the value is as above and at 2000 rpm the applicable limit is Tier I 9.8, Tier II 7.7, Tier III 2.0 g/kWh.
• For n >= 2000 rpm (high-speed engines): Tier I = 9.8, Tier II = 7.7, Tier III = 2.0 g/kWh.

Applicability by date/construction:

• Tier I: engines installed on ships constructed (keel laid or major conversion) after 1 January 2000.
• Tier II: engines installed on ships constructed after 1 January 2011.
• Tier III: engines installed on ships constructed after the NECA operative date (North America and United States Caribbean Sea ECAs from 1 January 2016; Baltic Sea and North Sea ECAs from 1 January 2021), and which are operated only within those Emission Control Areas. Outside the ECAs Tier II applies. Some engine types (e.g. those for emergency use, or engines on ships whose boundary is restricted) may be exempted. All such engines must be certified under the NOx Technical Code and carry an EIAPP Certificate.

(Refer to detailed answer above: purpose to document the engine particulars and the settings/configuration by which NOx compliance is achieved, so surveyors/regulators can verify; contents: engine design data, rated speed/power, the certified NOx value and limit, description of the emission control technology and parameters, the "engine configuration" / adjustment values, the retrofit and setting-up procedure, and maintenance/records, plus a record of engine adjustments and any modifications.)

(Refer to detailed answer above: check EIAPP and NOx Technical File validity and engine particulars; confirm the engine configuration matches the Technical File (no unauthorised adjustment); carry out an operational NOx verification test against the NOx Technical Code; verify any SCR/EGR/water-in-fuel emission control devices are functional and consumables available in ECAs; review engine adjustment/log and modification records; enforce correction and re-certification where a non-conformity is found; and align with port/fuel sampling and the flag/port inspection records.)