When the regulations were debated in 2006-2010, it was said that particles caused 50.000 premature deaths per annum only in Europe and shipping had become a major contributor compared to land-based activities that had succeeded in reducing particulate emission. As for the land-based industry, it was found that the most efficient measure would be to remove the SOx and NOx gases forming a large portion of the particles when released to the atmosphere.

Shipping has for several decades been propelled by High Sulfur Fuel Oil (HSFO) – the last liquid cut in the refinery process. The large bore low-speed propulsion engines onboard ships are ideal machinery for burning HSFO and as such shipping is a very complementary user of low-end products from the oil refinery industry.

The high sulfur content in HSFO stems from the refining process. As lighter fractions are taken out the concentration of sulfur increases and end up in the HSFO. When IMO decided to reduce the sulfur emission they recognized it would be challenging and decided to open up for “all roads to Rome” – desulfurization  of HSFO making LSFO (Low Sulfur Fuel Oil), reformation of HSFO to lighter distillates, other fuel type (LNG, LPG, Methanol etc) and EGCS (Exhaust Gas Cleaning System) or so-called scrubbers. For the existing fleet LSFO, MDO/MGO (Marine Diesel Oil/Marine Gas Oil) and EGCS are the most relevant alternatives.

The three alternatives have pros et cons when compared:

Air emissions

LSFO: Ash and soot particles as of today when burning HSFO without EGCS

MDO/MGO: Less particle mass, but a larger number of nanocarbon particles. Recent research has identified increased human tissue toxicity from distillate emissions when compared to HSFO emissions.

EGCS: Ash and Soot particles are partly emitted to air and partly captured by the EGCS

Water and land emission:

LSFO: The air born particles will eventually end in the sea or on land

MDO/MGO: The air born particles will be widely spread and eventually end up in the sea or on land

EGCS: The air born particles will eventually end in the sea or on land. The particles captured by the EGCS will end up in the sea close to the ship. Sulfur dioxide captured from the exhaust ends up as harmless sulfate in the sea. pH in discharge water drops to about 3 at the outlet but is subsequently raised to 6,5 at 4m from the ship side.

Additional CO2 footprint:

Photo: @mikes1978

LSFO: Large scale desulfurization of HSFO is energy and resource-demanding irrespective if being a hydro process (consuming hydrogen) or other catalysts/oxidation/mechanical excitation processes. The higher CO2 footprint and consume of precious hydrogen (hydro process), make this alternative less favorable energy-wise, than the ready to use HSFO.

MDO/MGO: Reformation of HSFO to distillate is an energy-intensive process and approximately 350 kg of CO2 is generated when converting a ton of HSFO to distillate. Forced processing of more crude to produce more distillate may yield 1-2% extra CO2

EGCS: The extra CO2 footprint is in the region 3% of treated fuel. Caused by the power to run EGCS and the SO2/CO2 swap in Sea Water.

A recent study by Chief Scientist Dr. Elizabeth Lindstad, published by Norway’s SINTEF, concludes that HFO with a scrubber is the most environmentally beneficial means of meeting GHG emissions targets even when taking into account LNG as an alternative fuel. Her study concluded that “With new modern refineries set up to convert crude into higher-priced products, high sulfur fuel oil (HSFO) will, from 2020, be delivered from existing refineries where its share of energy consumption can be considered to be next to nothing. The explanation is that the heavy bunker oil coming out from the refinery is the bottom of the barrel. If we acknowledge the lower energy consumption in delivering HSFO and deduct the refining we get nine to 10g of CO2 equivalent per MJ for HFO, rather than 13 to 15 of CO2 equivalent per MJ for LSFO/MGO.” The industry body Clean Shipping Alliance 2020 Executive Director Ian Adams said the industry has long realized that there is an energy penalty differential in the production of fuels. “Using higher sulfur fuels with an exhaust gas cleaning system will have a beneficial impact on the global reduction of sulfur and nitrogen oxides emissions and also on greenhouse gas (GHG) emissions.”

Resource utilization

LSFO: Costly process with high consumption of energy, Hydrogen, and Catalysts.

MDO/MGO: Shipping becomes a competitor to road transport and agriculture. If shipping will be 100% propelled by distillate about 10% of the world’s diesel pool will go to shipping. More crude will have to be produced and more HSFO needs to find other users.

EGCS: As per today, shipping is the complementary taker of the last liquid cut from the refinery process.


LSFO: Large investment in refinery processes. Medium to high fuel cost.

MDO/MGO: High fuel cost.

EGCS: High investment cost onboard. Low fuel cost.


LSFO: Compatibility issues threatening the safe operation of the ship. Bunkers will have to be segregated to avoid compatibility issues. Fuels from unusual streams and even unsuitable streams will be used as cutter stocks.

MDO/MGO: Viscosity and compatibility issues if switching between the two fuel alternatives LSFO and MDO/MGO to meet both 0,5% and 0,1% limits (ECAs)

EGCS:Safe operation as of today. Sensitive areas can be shielded from emission to water through a temporarily closed-loop operation.

All these alternatives come with some “pain” while meeting the objective to reduce health damages caused by particulate matters. They are all needed to achieve a global regulation together with alternatives like LPG/LNG, Methanol, hybrid solutions which are more relevant for new buildings. Collectively the efforts and extra costs to comply with Annex VI, do spur the research and development of alternative energy carriers which paves the road also for CO2 emission reductions called for. As such, none of the alternatives should be discarded. And when EGCS is accused of “transferring an air pollution problem to the sea”, then this is true for all combustion processes emitting exhaust that eventually ends up in the ocean or on land.

The difference is the capture of SO2 and the subsequent emission of sulfate to sea. When IMO considered the EGCS as an equivalent measure, thorough studies were made regarding emissions to sea and particularly the discharge of sulfate. The ocean contains large amounts of sulfate which also is a prerequisite for all life. The additional sulfate if all vessels in the world should have EGCS was found to be insignificant and absolutely harmless. The lowering of the pH in discharge water following the capturing of sulfur dioxide (SO2) is mainly a local issue which is countered by the regulation to raise pH > 6,5 at 4-meter distance from the outlet. Any discharge of low pH water is unwanted in view of the ongoing acidification when the ocean takes up CO2. But the contribution by EGCS in this context is truly negligible. When comparing the pros et cons there is no reason to say that EGCS is more “painful” than other alternatives. It simply does its job, contributing to saving the thousands of premature deaths caused by particulate matters.