International regulations to control harmful emissions from ships’ exhausts enter into force on 19 May 2005.
Regulations for the Prevention of Air Pollution from Ships are contained in Annex VI of the MARPOL Convention  and were adopted in the 1997 Protocol to that Convention.
The Annex VI regulations set limits on sulphur oxide (SOx) and nitrogen oxide (NOx) emissions from ship exhausts and prohibit deliberate emissions of ozone-depleting substances.
Sulphur content of fuel
The Annex includes a global cap of 4.5 percent by mass (% m/m) on the sulphur content of fuel oil and calls on IMO to monitor the worldwide average sulphur content of fuel once the Protocol comes into force.
Annex VI contains provisions allowing for special “SOx Emission Control Areas” (SECAs) to be established with more stringent controls on sulphur emissions. In these areas, the sulphur content of fuel oil used
onboard ships must not exceed 1.5% m/m.
Alternatively, ships must fit an exhaust gas cleaning system or use other methods to limit SOx emissions. The regulation requires such alternative methods to be approved by the Administration (flag State). Draft Guidelines on on-board exhaust gas-SOx cleaning systems have been developed and are expected to be approved by IMO’s Marine Environment Protection Committee
(MEPC) when it meets for its 53rd session in July 2005.
The Baltic Sea Area is designated as a SECA in the Protocol. However, the regulation allows for a 12-month period from the date of entry into force before the limits in a SECA can be enforced
In March 2000, the MEPC approved a proposed amendment to Annex VI to also include the North Sea as a SECA. The aim is to adopt the amendment once MARPOL Annex VI enters into force. It is anticipated that the MEPC will adopt amendments to Annex VI, including the proposed North Sea SECA, at its 53rd session to be held from 18-22 July 2005. The entry into force date is anticipated to be November 2006, with a 12 month period after that date before full implementation of the North Sea SECA.
Monitoring of sulphur content
IMO has been monitoring the worldwide average sulphur content of residual fuel supplied for use on board ships since 1999 following the adoption of resolution MEPC.82(43) Guidelines for monitoring the world wide average sulphur content of residual fuel supplied for use on board ships . The monitoring is based on bunker reports around the world representing more than 60 per cent of all bunkers delivered to ships. The worldwide average for 2004 has been calculated to be 2.67% m/m sulphur content. This figure has been almost constant since 1999 (the variation is less than +/- 0.02 % m/m).
Annex VI prohibits deliberate emissions of ozone-depleting substances, which include halons and chlorofluorocarbons (CFCs). New installations, such as refrigeration and fire-fighting systems, containing ozone-depleting substances, are prohibited on all ships, but new installations containing hydro-chlorofluorocarbons (HCFCs) are permitted until 1 January 2020.
Emissions of nitrogen oxides
Annex VI also sets limits on emissions of nitrogen oxides from diesel engines. A mandatory NOx Technical Code establishes procedures for the testing, survey and certification of marine diesel engines which will enable engine manufacturers, shipowners and Administrations to ensure that all applicable marine diesel engines comply with the relevant limiting emission values of NOx as specified in regulation 13 of Annex VI.
The Annex also prohibits the incineration aboard ship of certain products, such as contaminated packaging materials and polychlorinated biphenyls (PCBs), which have previously been used in a number of industrial materials.
Greenhouse gas policy
In November 2003, IMO adopted resolution A.963(23) IMO Policies and practices related to the reduction of greenhouse gas emissions from ships. The MEPC is developing draft Guidelines on the CO2 Indexing Scheme and has recognized that IMO guidelines on greenhouse gas emissions have to address all six greenhouse gases covered by the Kyoto Protocol: carbon dioxide (CO2); methane (CH4); nitrous oxide (N2O); hydrofluorocarbons (HFCs); perfluorocarbons (PFCs); and sulphur hexafluoride (SF6).