Historic Background

The issue of controlling air pollution form ships - in particular, noxious gases from ships' exhausts - was discussed in the lead up to the adoption of the 1973 MARPOL Convention. However, it was decided not to include regulations concerning air pollution at the time.

Meanwhile, air pollution was being discussed in other arenas. The 1972 United Nations Conference on the Human Environment in Stockholm marked the start of active international cooperation in combating acidification, or acid rain. Between 1972 and 1977, several studies confirmed the hypothesis that air pollutants could travel several thousand kilometres before deposition and damage occurred. This damage includes effects on crops and forests.

Most acid rain is caused by airborne deposits of sulphur dioxides and nitrogen oxides. Coal and oil-burning power plants are the biggest source of sulphur dioxides while nitrogen oxides come from car, truck - and ship - exhausts.

In 1979, a ministerial meeting on the protection of the environment, in Geneva, resulted in the signing of the Convention on Long‑range Transboundary Air Pollution by 34 governments and the European Community. This was the first international legally binding instrument to deal with problems of air pollution on a broad regional basis. 

Protocols to this Convention were later signed on reducing sulphur emissions (1985); controlling emissions of nitrogen oxides (1988); controlling emissions of volatile organic compounds (1991) and further reducing sulphur emissions (1994).

During the 1980s, concern over air pollution, such as global warming and the depleting of the ozone layer, continued to grow, and in 1987 the Montreal Protocol on substances that Deplete the Ozone Layer was signed.

The Montreal Protocol is an international environmental treaty, drawn up under the auspices of the United Nations, under which nations agreed to cut consumption and production of ozone-depleting substances including chlorofluorocarbons (CFCs) and halons in order to protect the ozone layer. 

A Protocol was adopted in London in 1990 - amending the original protocol and setting the year 2000 as the target completion date for phasing out of halons and ozone-depleting CFCs. A second Protocol was adopted in Copenhagen in 1992, introducing accelerated phase-out dates for controlled substances, cutting short the use of transitional substances and the introduction of phase-out dates for HCFCs and methyl bromide (a pesticidal gas which depletes the ozone layer).

CFCs have been in widespread use since the 1950s as refrigerants, aerosol propellants, solvents, foam blowing agents and insulants. In shipping, CFCs are used to refrigerate ship and container cargo, insulate cargo holds and containers, air condition crew quarters and occupied areas and refrigerate domestic food storage compartments.

Halons, manufactured from CFCs, are effective fire extinguishers used in portable fire extinguishers and fixed fire prevention systems.

IMO Begins Work on Air Pollution

At IMO, the Marine Environment Protection Committee (MEPC) in the mid-1980s had been reviewing the quality of fuel oils in relation to discharge requirements in Annex I and the issue of air pollution had been discussed.

In 1988, the MEPC agreed to include the issue of air pollution in its work programme following a submission from Norway on the scale of the problem. In addition, the Second International Conference on the Protection of the North Sea, held in November 1987, had issued a declaration in which the ministers of North Sea states agreed to initiate actions within appropriate bodies, such as IMO, "leading to improved quality standards of heavy fuels and to actively support this work aimed at reducing marine and atmospheric pollution".

At the next MEPC session, in March 1989, various countries submitted papers referring to fuel oil quality and atmospheric pollution, and it was agreed to look at the prevention of air pollution from ships - as well as fuel oil quality - as part of the committee's long-term work programme, starting in March 1990.

In 1990, Norway submitted a number of papers to the MEPC giving an overview on air pollution from ships. The papers noted:

  • Sulphur emissions from ships' exhausts were estimated at 4.5 to 6.5 million tons per year - about 4% of total global sulphur emissions. Emissions over open seas are spread out and effects moderate, but on certain routes the emissions create environmental problems, including English Channel, South China Sea, Strait of Malacca.
  • Nitrogen oxide emissions from ships were put at around 5 million tons per year - about 7% of total global emissions. Nitrogen oxide emissions cause or add to regional problems including acid rain and health problems in local areas such as harbours.
  • Emissions of CFCs from the world shipping fleet was estimated at 3,000-6,000 tons - approximately 1% to 3% of yearly global emissions. Halon emissions from shipping were put at 300 to 400 tons, or around 10% of world total.

Adoption of Resolution

Discussions in the MEPC and drafting work by a working group, led to the adoption in 1991, of an IMO Assembly Resolution A.719(17) on Prevention of Air Pollution from Ships. The Resolution called on the MEPC to prepare a new draft Annex to MARPOL on prevention of air pollution.

The new draft Annex was developed over the next six years - and was finally adopted at a Conference in September 1997. It was agreed to adopt the new Annex through adding a Protocol to the MARPOL Convention, which included the new Annex. This enabled specific entry into force conditions to be set out in the protocol.

The Protocol of 1997 (MARPOL Annex VI)

The Protocol adopted in 1997 included the new Annex VI of MARPOL, which entered into force on 19 May 2005.

MARPOL Annex VI sets limits on sulphur oxide and nitrogen oxide emissions from ship exhausts and prohibits deliberate emissions of ozone depleting substances. The annex includes a global cap of 4.5% m/m on the sulphur content of fuel oil and calls on IMO to monitor the worldwide average sulphur content of fuel.

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 any other technological method to limit SOx emissions. The Baltic Sea Area is designated as a SOx Emission Control area in the Protocol. The North Sea was adopted as SOx Emission Control Area in July 2005.

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. A mandatory NOx Technical Code, which defines how this shall be done, was adopted by the Conference under the cover of Resolution 2. The Annex also prohibits the incineration onboard ship of certain products, such as contaminated packaging materials and polychlorinated biphenyls (PCBs).