Reduction in Sulphur Oxides Emissions – Legislative Intervention Reaps Positive Results

Reduction in Sulphur Oxides Emissions – Legislative Intervention Reaps Positive Results

Author: Matthew Cassar


Indisputably, ships play a major role in world trade (as 90% of world trade is carried out on sea). Proportionately ships are responsible for the release of certain emissions impacting marine environment and global health generally. As world trade inherently depends on the shipping industry, international bodies face increased responsibility to augment global maritime regulations to ensure minimal environmental impact by the industry as a whole and the safeguarding of human health.

The utilisation of marine fuel is one of the major offenders impacting global environmental and human health. A biproduct of burning marine fuel, which fuel is generally composed of a mixture of heavy fuel oil and diesel oil, is the emission of significant amounts of particulate matter such as sulphur oxides (SOx). Particularly, marine fuels with a high sulphur content produce considerable sulphur dioxide which is emitted from a ship’s exhaust gas. Amongst the multifaceted health hazards associated with the release of sulphur dioxide in the atmosphere, sulphur dioxide can have profound harmful effects on the human health particularly the respiratory system whilst it is also one of the prime instigators of the universally harmful acid rain. It is estimated that around 300,000 premature deaths per year are attributable to chronic exposure to fine particulate matter. Additionally, a recent study has estimated that ship-related pollution is responsible globally for around 14 million childhood asthma cases.

Legislative Intervention

Taking cognizance of all these facts, the International Maritime Organisation (IMO), which organisation is responsible for, amongst a plethora of other matters, overseeing ship safety and security and the prevention of water and sea pollution from ships. On 26th October 2017 they decided to intervene legislatively with the intent to reduce the amount of sulphur dioxide generated by the shipping industry. The legislative intervention came in the form of the implementation of a sulphur content limitation, which meant that a 0.50% mass by mass (m/m) sulphur content cap on all marine fuel, outside designated emission control areas, was to be enforced by 2020. Keeping its promise, on 1 January 2020, the limit on sulphur content was enacted into law following an amendment to Annex VI of the International Convention for the Prevention of Pollution from Ships (MARPOL).

The significance of this legislative intervention, termed “IMO 2020”, cannot be overstated. Marine fuels containing heavy fuels oils, which have a considerably higher sulphur content compared to other fuels, have been the backbone of the shipping industry for a considerable number of years. “IMO 2020” has effectively scaled back the acceptable sulphur content limit of all marine fuel by a not so insignificant 3% from the previous 3.5% mass by mass (m/m) sulphur content cap to 0.5%, for context purposes, the sulphur content of fuels used in trucks or passenger cars must not exceed 0.001%. The shipping industry has had to react decidedly to ensure compliance with the legislative limitation. Compliance has generally taken two forms: the utilisation of marine fuel which complies with the sulphur cap introduced by “IMO 2020” or through the installation of emission abatement technology (scrubbers) on board vessels, which essentially clean the emissions before they are released into the atmosphere. Scrubbers effectively function by reacting acidic exhaust gases produced by ships with an alkaline scrubbing material to ensure that sulphur emissions match mandated levels.

Significant Results        

On the 7th of September 2022, IMO stated that since 1 January 2020 and the entry into force of “IMO 2020”, and therefore the implementation of the sulphur cap, an estimated 77% drop in overall sulphur oxide emissions in ships was recorded. This translates to an estimated reduction of 8.5 million metric tonnes of sulphur oxides, in short, a roaring success for “IMO 2020” and the safeguarding of our global environment and human health. And the success story does not stop there (as “IMO 2022” seems to be best thing since sliced bread!). In October 2022, NASA (National Aeronautics and Space Administration) shared the results of a study it carried out which indicated that “ship-track clouds” dropped dramatically in 2020, the first year of the implementation of “IMO 2020”.

Ship-tracks (or as they are defined by NASA, “ghostly fingerprints”) are the result of water vapour coalescing around small particles of pollution (aerosols) in ship exhaust. These droplets, which are far more full-bodied in comparison to droplets of normal water vapour, have the effect of scattering rays of light and thereby illuminating to a greater degree when compared to marine clouds which are not polluted. The success of “IMO 2020” can be measured in that NASA’s study found that in 2020 ship-track density decreased significantly in every major shipping lane. One could argue that this reduction may be a direct result of the disruptions caused to the shipping industry due to the COVID-19 pandemic. Fortuitously, data has indicated that this is not the scenario at hand as ship tracking data indicated that global shipping traffic decreased by only 1.4% for a few months and this decrease could not account for the significant decrease in observed ship-tracks.

Extending Designated Emission Control Areas

The year 2022 has brought with it a further important milestone in the reduction of sulphur emissions. Not willing to rest on its laurels in terms of safeguarding marine environment and human health, the IMO has this year agreed to designate the entire Mediterranean Sea as an emission control area. This means that ships will from 2025 have to comply with more stringent controls on sulphur oxide emissions. Emission control areas are designated areas wherein a 0.10% mass by mass (m/m) sulphur content cap is applicable. Currently the Baltic Sea area, the North Sea area, the North American area (covering designated coastal areas off the United States and Canada), and the United States Caribbean Sea area (around Puerto Rico and the United States Virgin Islands) are the only emission control areas and with IMO’s decision through MEPC 78, the Mediterranean Sea set to join this list in 2025. This assuredly augurs well for the future of marine environment and human health.

Possible Pitfalls

Whilst “IMO 2022” has resulted in quantifiable positive impact on global environment and human health as a whole, it is not without its possible pitfalls. Concerns and controversies have arisen with respect to the use of scrubbers and emission abatement technology. The root of the concern and controversy stems from ships having “open-loop systems” onboard which effectively means that harmful emissions are treated with a scrubbing medium, generally seawater, following which this scrubbing medium or treated seawater is released into the sea. Understandably, stakeholders are concerned that as a result of a lack of proper treatment of the scrubbing medium and/or the illegal discharge of the said medium into sea water “IMO 2020” might result in the unintentional rise in sea pollution. Essentially this would shift the problem elsewhere without resolving it.


IMO is understandably buoyant with the positive and successful results brought about by “IMO 2022” as these results are unmistakably a cause for celebration. The future augurs well for similar legislative interventions. Whilst IMO continues to strengthen its legislative reach with respect to safeguarding the environment and human health it would do well to address any possible pitfalls. On the balance of things however it would appear that positive strides forwards have been made.

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