Biodiesel use in shipping can reduce black carbon emissions by as much as 81% compared with marine gas oil, according to real-world operating data generated by Project CLEANSHIP and submitted to the International Maritime Organization (IMO).

The measurements were carried out on the Uni-Tankers A/S vessel Falstria Swan during normal commercial operations while running on B100 fatty acid methyl ester (FAME) biodiesel. Emissions were monitored in real time using an online black carbon sensor developed by Green Instruments in collaboration with the Danish Technological Institute.

The data showed that black carbon reductions were most pronounced at lower engine loads, a finding that researchers described as particularly relevant for vessels operating in coastal and emission-sensitive regions. Black carbon, a component of soot, is recognised for its disproportionate warming effect, its role in accelerating Arctic ice melt, and its contribution to local air quality.

Simon Martin Spangenberg Bastrupberg, consultant and measurement specialist in alternative fuels and emission reduction at Danish Technological Institute, said: "We expected that biofuel would lead to cleaner combustion, but the magnitude of the reduction, especially at lower engine loads, is a very positive surprise. This demonstrates that biodiesel can reduce not only net CO₂, but also black carbon, which is highly significant for the shipping sector's total climate footprint."

From an operator perspective, Uni-Tankers said the findings provide practical insight into the emissions profile of biodiesel use at sea. Troels Reppien, technical director at the company, stated: "The latest real-world sailing data on biodiesel (B100) give us a clear picture of both the black carbon footprint and actual CO₂ emissions. This insight is crucial for achieving our own reduction targets, while also contributing to better, data-driven recommendations for reducing emissions across the shipping industry."

Project CLEANSHIP noted that while biodiesel demonstrates clear emissions benefits, current global biofuel production is only capable of supplying a limited share of total shipping energy demand. Further work under the project will focus on refining recommendations for reducing black carbon and other pollutants across different vessel types and operating profiles.

The findings have been submitted to the IMO in the form of a white paper and are scheduled for consideration at the 13th session of the Sub-Committee on Pollution Prevention and Response, to be held from 9–13 February 2026.