If IMO 2020 was the headline, MARPOL Annex VI is the rulebook behind it. This is the international convention chapter that governs air pollution from ships — and in 2026 it reaches well beyond sulphur into nitrogen oxides and, increasingly, greenhouse gases. Every operator trading internationally needs to understand what it requires.
What MARPOL Annex VI Covers
Annex VI of the International Convention for the Prevention of Pollution from Ships (MARPOL) sets limits on the main air pollutants from ship exhaust and machinery. Its scope breaks into a few pillars:
- Sulphur oxides (SOx) — the 0.50% global cap and 0.10% ECA limit on fuel sulphur.
- Nitrogen oxides (NOx) — tiered engine emission standards (Tier I, II and the strict Tier III inside NOx ECAs).
- Ozone-depleting substances — controls on certain refrigerants and fire-fighting agents.
- Volatile organic compounds (VOCs) — particularly for tankers.
- Energy efficiency & greenhouse gases — EEXI, the SEEMP, and the operational CII rating.
NOx Tiers in Plain English
Marine diesel engines must meet NOx limits based on when the ship was built and where it operates. Tier I and II apply globally by build date; Tier III applies to newer engines operating inside designated NOx Emission Control Areas and demands roughly an 80% reduction versus Tier I — usually achieved with selective catalytic reduction (SCR) or exhaust gas recirculation (EGR).
The Certificate That Proves Compliance
A ship demonstrates Annex VI compliance with the International Air Pollution Prevention (IAPP) Certificate, supported by the engine's technical file and NOx Technical Code documentation. Port state control will check it, and an invalid or missing certificate is a detainable deficiency.
The Greenhouse-Gas Layer (EEXI & CII)
Since 2023, Annex VI also drives decarbonisation. The Energy Efficiency Existing Ship Index (EEXI) is a one-time technical requirement, while the Carbon Intensity Indicator (CII) gives ships an annual operational rating from A to E. Ships rating poorly must produce a corrective action plan. In 2026 this is where most operator attention sits, because a weak CII trajectory can affect charter attractiveness and, eventually, trading freedom.
What Operators Should Do
- Keep the IAPP certificate and technical file current and accessible;
- Buy compliant fuel and sample every stem (see our IMO 2020 guide);
- Track CII performance through the year, not just at the annual reckoning;
- Maintain SCR/EGR and scrubber systems so they pass survey and actually perform.
Procurement's Role
Clean compliance starts with what you buy — compliant fuel, certified equipment, and the consumables that keep emission-control systems running. The GDS platform connects operators with verified suppliers for compliant fuel and marine equipment, with documentation kept in one place. Register your fleet to simplify compliant procurement.
