MARPOL Annex VI — Prevention of Air Pollution

Annex VI fuel, engine and emission requirements, with distinct scopes and dates for NOx, SOx, SEEMP, DCS and CII.

Operational Explanation

MARPOL Annex VI governs the prevention of air pollution from ships: sulphur oxides (SOx) and fuel quality, nitrogen oxides (NOx), ozone-depleting substances (ODS), volatile organic compounds (VOCs), on-board incineration, and — from Chapter 4 — energy efficiency and greenhouse gas emissions (EEDI, EEXI, SEEMP, CII, IMO DCS).

To use this framework on the ship, start with the route, engines and installed equipment: identify the applicable branch and connect it to the certificate, approved configuration and relevant records. Keep onboard checks distinct from data to be reported, coordinating bridge, engine department and Company under their respective procedures. The following sections organise these areas and refer to specific operational topics, including Fuel Oil Changeover and Incinerator Operations.

NOx: Regulation 13 and the three Tiers

Regulation 13 concerns marine diesel engines >130 kW within its scope, subject to exclusions and specific regimes. Cycle-weighted emissions are expressed in g/kWh NO₂ equivalent and depend on n, rated speed in rpm. The table summarizes limits, not the applicability assessment.

The Tier depends on engine, ship, date and area, not ship age alone. Distinguish original engine, identical/non-identical replacement, additional engine and other major conversions (13.2, amended by MEPC.385(81), also covering diesel engines replacing a steam system). Check the intervention date, any recognized exemption, EIAPP and Technical File. A 2005 ship with its original engine does not automatically become Tier II; a later non-identical engine is not assessed solely against 2005.

Where 13.5.3 applies, record Tier and on/off status on entering/leaving the NOx ECA and at status changes within it, with date, time and position. The SOx fuel-change log does not replace these NOx records.

Exclusions. Regulation 13 does not apply to engines intended solely for emergencies, nor to engines installed in lifeboats, nor to engines on ships engaged solely on voyages within waters under the sovereignty or jurisdiction of the flag State, provided the engine is subject to an alternative NOx control measure established by the Administration. Excluded from Tier III only are, in addition, recreational craft of less than 24 metres in length specifically designed and used solely for recreation, and ships with a combined nameplate propulsion power of less than 750 kW that demonstrate to the Administration that they cannot comply because of design or construction limitations. Regulation 13.5.2.3 also excludes from Tier III engines on ships built before 1 January 2021, below 500 GT, with length L of at least 24 m, specifically designed and used solely for recreation. There is finally a regime of its own (Reg. 13.7) for engines with a power output of more than 5000 kW and a per-cylinder displacement at or above 90 litres installed on ships constructed on or after 1 January 1990 and prior to 1 January 2000: for those, where certified, an Approved Method applies.

“ECA” is not one single thing: Regulation 14 for SOx and particulate matter, Regulation 13 for NOx

This is the confusion that derails a voyage plan. Annex VI has two lists of areas, in two different Regulations, with different perimeters and different dates. Regulation 14 — whose full title is “Sulphur oxides (SOx) and particulate matter” — lists the areas where the 0.10% m/m sulphur limit applies. Regulation 13 separately lists the “NOx Tier III emission control area”. An area may sit in one list, in the other, or in both.

It is not correct to say that the Mediterranean is an ECA for sulphur only: the Regulation 2 definition knows three combinations, not four, and names them thus: “air pollution from NOx or SOx and particulate matter or all three types of emissions”. SOx and particulate matter travel together, always. Every Regulation 14 area is an ECA for sulphur AND for particulate matter, the Mediterranean included; the official name of the Mediterranean area is in fact “Mediterranean Sea Emission Control Area for Sulphur Oxides and Particulate Matter”. The real difference is another: the Mediterranean is the only area that sits on the Regulation 14 list and not on the Regulation 13 one.

One fact surprises anyone looking for a number: Annex VI sets no numerical limit for particulate matter. PM appears in the title of Regulation 14, in the Regulation 2 definition and in the designation criteria, but it has neither g/kWh nor mg/m³. It is controlled indirectly, through the sulphur content of the fuel or an equivalent means approved under Regulation 4. The contrast with NOx is sharp: there the numbers exist, and they are those in the table above.

Chapter 4: respect regulation 19 exclusions and relevant categories. SEEMP Part I has its own scope; DCS/Part II concerns the ≥5,000 GT branch of regulation 27; CII/Part III concerns only the ≥5,000 GT categories listed in 28.1, not all DCS ships. Part II Confirmation, IAPP and annual Statement are different documents. Circ.913 distinguishes early 2025 implementation, ordinary existing-ship collection from 2026 and ships delivered on or after 1 August 2025 with enhanced granularity from delivery; see the DCS page for plan revision/verification.

The Net-Zero framework remains unadopted. Resumption of the extraordinary session proposed for 4 December 2026 is subject to confirmation at MEPC 85; it is not an entry-into-force date.

Regulatory Reference

For the North-East Atlantic ECA, the adopted text of MEPC.407(84), annex 3 to the MEPC 84 report, is available. The IMO Knowledge Centre entry consulted on 16 October 2026 still states “awaiting certification”: availability of the adopted text and the status of that entry are distinct information. Read the future timetable and applicable conditions in the instrument without anticipating its effect.

Base text MEPC.328(76) with relevant amendments: MEPC.385(81) (fuels/DCS), MEPC.392(82) and MEPC.407(84) (ECAs). NOx: regulation 13 and Technical Code 2008; SOx/PM: 4 and 14; ODS: 12; VOC: 15; incineration: 16; BDN: 18; efficiency/data: chapter 4.

For SOx/PM check compliant fuel or a regulation 4 approved equivalent for the consumers covered. The >0.50% fuel-for-use carriage ban does not exclude the approved-equivalence route and does not concern the product carried as cargo. Merely having an EGCS that is not approved/applicable or operational is insufficient; also check local restrictions on its discharges.

Scope of Application

The Annex has differentiated requirements: IAPP under 5–6; NOx by engine/13; EEXI for the specified ≥400 GT categories; DCS and CII with distinct scopes. Belonging to one branch does not establish applicability of all the others.

Regulation 12 — ozone-depleting substances (ODS). Deliberate emissions are prohibited, subject to the regulation’s limited qualifications. New installations containing non-HCFC ODS have been prohibited under the 19 May 2005 branch and new HCFC installations under the 1 January 2020 branch. Removed substances and equipment must go to appropriate reception facilities. Every ship subject to Regulation 6.1 must maintain a list of ODS-containing equipment; where rechargeable systems are present, it must also maintain an ODS Record Book and promptly record quantities in kilograms for recharge, repair/maintenance, deliberate or non-deliberate release to atmosphere, landing to reception facilities and supply to the ship.

Procedure / How to Complete It

1. For ODS, verify the equipment list and installation dates, prevent deliberate emissions, use the ODS Record Book for rechargeable systems, record each Regulation 12.7 event promptly in kilograms and retain evidence of landing removed substances/equipment to an appropriate reception facility.
2. Check the ship’s IAPP and survey calendar. For relevant engines check EIAPP, identity/configuration, approved Technical File, changes and in-service verification method: do not assign an IAPP-like five-year renewal to the EIAPP.
3. For the voyage, connect each consumer with compliant fuel or the approved equivalent that covers it. Check actual configuration and operation, area limits and local EGCS restrictions; use the specific procedure when a changeover is needed.
4. For each relevant engine, establish its identity and the date and type of intervention and compare them with the regulation 13.2 branch and EIAPP/Technical File. Distinguish the original engine, identical or non-identical replacement, additional engine and other major conversions.
5. Where 13.5.3 applies, record Tier and on/off status on entering/leaving the NOx ECA and at status changes within it, with date, time and position. The SOx fuel-change log does not replace these NOx records.
6. Check BDN and samples by fuel regime; do not apply conventional sampling to gas/low-flashpoint fuels.
7. Separate SEEMP/DCS checks from CII checks: verify regulation 19 exclusions, relevant tonnage and categories, the plan and applicable Confirmation. For collection granularity and timing use Circ.913 cited above and the DCS topic, keeping the annual Statement distinct.

Practical Example

The two SECAs do not touch. The Mediterranean ends at the western entrance to the Strait of Gibraltar, on a line joining Cape Trafalgar and Cape Spartel. The North Sea begins, to the west, only at “the English Channel and its approaches eastwards of longitude 5° W and northwards of latitude 48°30' N”. In between lie the Gulf of Cadiz, the Iberian Atlantic coast and the Bay of Biscay: waters where the global 0.50% m/m limit applies today, not 0.10%.

In September 2026 a Mediterranean–Northern Europe route may cross two SOx transitions. This does not require two switches: one 0.10% fuel, separate fuels and an approved equivalent have different routes. A company may voluntarily use cleaner fuel outside an ECA.

From 1 September 2028 NE Atlantic SOx/PM limits create continuity on routes remaining within its official boundary and adjacent ECAs. Applicable Tier III starts with entry into force on 1 September 2027 subject to its conditions. Do not infer limits for an entire route from its destination alone.

What Typically Goes Wrong

Common Mistakes Mistake Library

What the PSCO Checks

A PSCO may compare relevant certificates/documents, actual configuration, Technical File, data and operational records. IAPP, EIAPP, SEEMP Confirmation and annual Statement retain distinct roles and processes.

Operational Tips

• Include ODS equipment, recharge, maintenance, releases, supply and landing in the Annex VI control.
• Keep SOx and NOx maps/dates separate.
• Check engine, interventions and Technical File, not just ship age.
• Check Tier/status records where required.
• Apply DCS and CII only within their respective scopes.

Preparation checklist

Educational checklist. This summary supports learning and preparation only. It does not replace the vessel’s approved procedures, manuals, statutory documents, company SMS, or applicable official requirements. Completing it demonstrates neither compliance nor readiness for an inspection: it shows that a list has been read, not that the ship is in order. Always verify the current documents carried on board.

• ODS equipment list and, for rechargeable systems, Record Book and kilogram entries checked
• IAPP and ship surveys checked
• EIAPP/Technical File/configuration and engine interventions checked
• SOx: compliant fuel or approved equivalence for consumers covered
• NOx: area, dates, engine branch and 13.5.3 records
• BDN/samples according to fuel type
• SEEMP II/DCS and III/CII checked separately with relevant Confirmations

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Certified substantive revision: 16 October 2026 · page fingerprint 5f726b7a1f1d