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

• n < 130 rpm: Tier I = 17.0; Tier II = 14.4; Tier III = 3.4 g/kWh.
• 130 <= n < 2000 rpm: applicable value is interpolated logarithmically between the end points (the formula) - e.g. at n=2000 the limit for Tier II is 7.7 g/kWh, at n=130 it is 14.4.
• n >= 2000 rpm: Tier I = 9.8; Tier II = 7.7; Tier III = 2.0 g/kWh.

Dates:

• Tier I applies to engines installed on ships constructed after 1 January 2000.
• Tier II applies to engines installed on ships constructed after 1 January 2011.
• Tier III applies to engines installed on ships constructed after the NECA in-force date: North America and US Caribbean Sea Emission Control Areas from 1 January 2016; Baltic Sea and North Sea areas from 1 January 2021, when operating within those Emission Control Areas (ECA). Outside ECAs, Tier II remains the applicable limit.
• Any engine to which a NOx control method (e.g. an approved NOx reducing device) fitted must have the device certified and remain in compliance; operating methods that defeat emission control are prohibited.
• The NOx Technical Code prescribes survey and certification (EIAPP certificate) and the procedures to verify compliance.

Purpose: The NOx Technical File is a document (issued under the NOx Technical Code) that provides the necessary data and technical information to verify that a marine diesel engine complies with the applicable NOx emission limit under MARPOL Annex VI, and describes the components, settings and procedures by which compliance is achieved and maintained. It also enables the engine's NOx emission value to be verified during survey and investigation.

Key contents:

• Engine identification: manufacturer, model, engine number, rated power, rated speed and identification of the engine as installed.
• The applicable NOx emission limit (the limiting value) and the certified NOx emission value from the pre-certification test.
• A description of the emission control system/technology applied (e.g. in-built timing, injection adjustment, supercharging arrangement) and the "engine configuration parameter" (values that, if changed, invalidate compliance), as well as the "approved framework" (alternative method).
• The components and settings which define the emission level (the "adjusted certificates" - the set of engine components/settings).
• Instructions for the operator regarding controls, calibrations, adjustment, retrofit and the record of the engine's adjustments (the engine adjustment record use logs).
• On-board maintenance and the procedures to maintain compliance.
• Records of any modifications, with a section log to record major modifications that may affect emissions.

The file is maintained on board, and any modification that affects the NOx emission value must be recorded and re-verified appropriately.

• Verifying that the EIAPP (Engine International Air Pollution Prevention Certificate) and the NOx Technical File are on board and valid, and noting the engine particulars.
• Confirming the engine configuration is as documented in the NOx Technical File: check that the components and settings (rails, fuel injection timing, turbocharger, etc.) correspond to the certified design; check that no unauthorised adjustment has been made.
• Carrying out a practical NOx verification test (e.g. a test on an engine following the NOx Technical Code simplified emissions measurement/verification procedure) at the surveyor's request; this may sample the exhaust, using the engine test cycle to measure NOx (for example with a portable NOx analyser) comparing with the certified value.
• Confirming that any NOx reduction device (e.g. SCR, urea system) is functioning as required and that consumables (urea) are available and used when entering an ECA.
• Reviewing the NOx Technical File, the engine adjustment/use log and any record of modifications; also confirming compliance by fuel consumption and engine behaviour consistent with the certified settings.
• Where a vessel is found non-compliant (e.g. an altered setting), the flag/port state enforcement includes requiring the engine to be adjusted/certified again; record of the non-conformity is made.
• Periodic/port state checks by the regulatory authorities and the "NOx verification" under the NOx Technical Code Annex (the engine manufacturer verification).