Why reducing sulphur in shipping is vital
Mediterranean Sea named emission control area in effort to combat air pollution and impact on human health
Since the adoption of the MARPOL Convention in 1973, the IMO has played a central role in mitigating the environmental impact of shipping, particularly pollution caused by operational and accidental discharges.
While progress has been incremental, the regulatory framework has steadily evolved to address emerging environmental and public health concerns.
One of the most impactful milestones occurred on 1 January, 2020, when the global sulphur cap in marine fuel oil was reduced from 3.5% to 0.5% under MARPOL Annex VI. This initiative was designed to curtail sulphur oxide (SOx) emissions, thereby improving air quality and reducing associated health risks, particularly in densely populated coastal areas.
Building on this, the IMO designated the Mediterranean Sea as an Emission Control Area (Med SOx ECA), effective 1 May, 2025. Within this zone, marine fuels will be required to contain no more than 0.1% sulphur—a significant tightening of standards intended to further reduce air pollution and its impact on human health and the marine environment.
Price of fuel remains a major consideration
Both LSFO (Low Sulfur Fuel Oil) and VLSFO (Very Low Sulphur Fuel Oil) comply with the 0.5% sulphur limit, while Ultra-Low Sulphur Fuel Oil (ULSFO) and Low-Sulphur MGO (Marine Gas Oil) meet the stricter 0.10% requirement.
However, it’s important to note that despite meeting sulphur content thresholds, cheaper fuels such as VLSFO and ULSFO—being less refined—may contain higher levels of harmful substances including heavy metals, polycyclic aromatic hydrocarbons (PAHs), and mercury.
The use of exhaust gas cleaning systems (scrubbers) has enabled compliance with sulphur limits, but these systems often result in direct discharge of pollutants into the sea, when scrubbers are cleaned.
Additionally, the combustion of heavier fuel oils like VLSFO and ULSFO contributes significantly to particulate matter and black carbon emissions—pollutants with well-documented short-term climate and health effects.
In the Mediterranean, the transition to the more expensive MGO has produced observable improvements. Vessels previously required frequent deck washing to remove soot and ash (often discharged overboard), whereas ships now operating on MGO maintain cleaner decks for extended periods. This suggests a substantial reduction in particulate emissions, beyond the gains attributed solely to lower sulphur content.
Epidemiological data further support the benefits of emission controls. For instance, port city studies in Ancona, Italy have linked elevated levels of NO₂ and particulate matter to increased mortality rates. However, there remains a significant gap in research on the long-term health effects on seafarers, particularly regarding exposure based on onboard work location.
The Med SOx ECA demonstrates the tangible environmental and occupational health benefits of transitioning to cleaner fuels like MGO. While costlier, the use of highly refined fuels yields immediate reductions in both airborne and marine pollution.
A global shift toward the widespread use of MGO in the shipping sector—though not without financial implications—could deliver profound benefits for climate stability, environmental protection, and human health. Continued international collaboration and robust policy leadership are essential to ensure the sustainability of maritime operations in the decades to come.
This article represents the views and thoughts of the author, and not necessary of IMarEST.
Patrick Lyne primarily works with NGOs and the wider industry as a marine scientist and consultant in baseline data acquisition and mitigation as well as environmental assessment.
The Ship Energy and Environment Special Interest Group is looking for a chair and/or co-chair, and committee members to drive discussions and initiatives on energy efficiency and environmental performance in the maritime sector.
Image: scrubber operation on container vessel. Credit: Shutterstock.
