MARPOL Annex VI sets limits on air pollution from ships — primarily sulphur oxide (SOx) and nitrogen oxide (NOx) emissions, along with other air pollutant controls.
The Global Sulphur Cap
Since 2020, MARPOL Annex VI has capped fuel sulphur content at 0.5% globally (down from the previous 3.5%), with a stricter 0.1% limit inside designated Emission Control Areas (ECAs) covering parts of Europe, North America, and other sensitive regions. This forced a major industry shift: switching to low-sulphur fuel oil, installing exhaust gas scrubbers to continue using cheaper high-sulphur fuel while meeting emission limits, or adopting alternative fuels entirely.
NOx Emission Limits (Tiers)
Nitrogen oxide limits apply in tiers based on the engine’s build date and operating area — progressively stricter standards (Tier I, II, III) apply to newer engines, with Tier III specifically required in NOx Emission Control Areas, driving adoption of technologies like Selective Catalytic Reduction (SCR) and Exhaust Gas Recirculation (EGR).
Compliance Verification
Bunker Delivery Notes (BDN) documenting fuel sulphur content, along with the vessel’s IAPP (International Air Pollution Prevention) Certificate, are checked during Port State Control inspections — non-compliant fuel or falsified BDN records is a genuine, actively enforced violation with real financial and legal consequences.
Exam Relevance
MARPOL Annex VI’s sulphur cap, ECA requirements, and NOx tier system are core, current-events-relevant topics in deck and engineering officer competency exams.