From 1 January 2020, the limit for sulphur in fuel oil used on board ships operating outside designated emission control areas is reduced to 0.50% m/m (mass by mass), down from 3.50% m/m (a limit that was in effect since 1st January 2012).
The rules governing this are the regulations for the Prevention of Air Pollution from Ships (Annex VI) under the international MARPOL Convention. Annex VI seeks to control airborne emissions from ships (sulphur oxides (SOx), nitrogen oxides (NOx), ozone depleting substances (ODS), volatile organic compounds (VOC) and shipboard incineration) and their contribution to local and global air pollution, human health issues and environmental problems.
The date of 1 January 2020 was set in the regulations adopted in 2008. However, a provision was adopted, requiring IMO to review the availability of low sulphur fuel oil for use by ships, to help Member States determine whether the new lower global limit on sulphur emissions from international shipping shall come into effect on 1 January 2020 or be deferred until 1 January 2025. IMO’s Marine Environment Protection Committee (MEPC 70), in October 2016, decided that the 0.50% limit should apply from 1 January 2020.
Further information is found in this useful IMO Q&A – here.