Regulations for the Prevention of Air Pollution from Ships are set to enter into force on 19 May 2005, following the ratification of Annex VI of the International Convention for the Prevention of Pollution from Ships (MARPOL). Annex VI has now been ratified by states with 54.57% of world merchant shipping tonnage. It sets limits on sulphur oxide and nitrogen oxide emissions from ship exhausts and prohibits deliberate emissions of ozone-depleting substances.

Annex VI contains provisions allowing for special "SOx Emission Control Areas" to be established with more stringent controls on sulphur emissions. In these areas, the sulphur content of fuel oil used on board ships must not exceed 1.5% m/m. Alternatively, ships must fit an exhaust gas cleaning system or use any other technological method to limit SOx emissions. The Baltic Sea Area is designated as a SOx Emission Control area in the Protocol. Annex VI prohibits deliberate emissions of ozone depleting substances, which include halons and chlorofluorocarbons (CFCs). New installations containing ozone-depleting substances are prohibited on all ships. But new installations containing hydro-chlorofluorocarbons (HCFCs) are permitted until 1 January 2020. Annex VI also sets limits on emissions of nitrogen oxides (NOx) from diesel engines and prohibits the incineration on board ships of certain products, such as contaminated packaging materials and polychlorinated biphenyls (PCBs).