The IMO addresses air pollution through MARPOL Annex VI, regulating sulphur oxides (SOx), nitrogen oxides (NOx), and particulate matter from ships.

Since January 1, 2020, the global sulphur limit for marine fuel was reduced from 3.50% to 0.50% by mass (m/m). However, some regions, known as Emission Control Areas (ECAs), enforce stricter limits of 0.10% sulphur content. A list of special areas, including those under Annex VI, can be found here.

To meet the stricter limits, ships must flush their fuel system and use compliant 0.10% sulphur fuel before entering an ECA. This requires a ship-specific calculation based on system volume, sulphur contents and current consumption to determine changeover time. Fuel changeover details—including quantities, date, time, and position—must be logged. Switching back from compliant fuel should only begin after exiting the ECA.

Not all countries enforce sulphur content limits on ships because some have not ratified MARPOL Annex VI. A list of ratified countries can be found here.
What if a country has not ratified a MARPOL annex?

In non-ratifying countries we suggest shipowners consult local regulations and/or their flag state to determine the applicable sulphur cap. Similarly, ratifying countries may impose stricter local regulations than those outlined in MARPOL.

When higher sulphur fuels are allowed under local legislation, ensure sufficient changeover time before re-entering a MARPOL area, as lower fuel consumption at anchorage or port can extend the full system flush time.

Scrubber Use

In many ECAs, vessels can use exhaust gas cleaning systems (scrubbers) to meet the IMO 2020 global sulphur cap. Scrubbers remove sulphur from exhaust gases with wash water as a byproduct, allowing the use of higher-sulphur fuels when operated and maintained according to IMO guidelines in MEPC.340(77).

Scrubbers can be used in open-loop (discharging wash water directly into the sea) or closed-loop (treating and recirculating the wash water) modes. Local regulations vary by country, so shipowners should consult specific guidelines on open or closed-loop usage, our resource here can be used as a guide.

New ECA areas

The Mediterranean Sea has recently joined the list of ECAs, effective from 1 May 2025, details can be found here.

MEPC 82 introduced the Canadian Arctic and Norwegian Sea as new ECAs, targeting NOx emissions from March 1, 2026, and SOx emissions from March 1, 2027.
Source: North Standard