Airborne Measurements Reveal the Underestimated Impact of Black Carbon Emissions from Ships

The impacts of black carbon (BC) emissions on climate change, human health, and the environment are well-documented in scientific literature. In response, efforts have been made to reduce BC emissions, particularly in sectors such as energy production, industry, and road transport. However, the maritime shipping industry has largely been exempt from stringent BC emission regulations. While the International Maritime Organization (IMO) has established emission limits for pollutants such as SOx, NOx, and VOCs, as of today, BC emissions from ships are still unregulated at the international level. Whereas the IMO expected that BC emissions would be reduced with the adoption of the SOx regulations, especially within the sulphur emission control areas, this study found that these goals remain largely unmet. This research analyzes real-world BC emissions based on 886 measurements from ships operating in the southern North Sea. Results show that observed BC emission factors (EFs) are significantly higher than previously reported in the literature and those applied by the IMO. In particular, ships equipped with exhaust gas cleaning systems (EGCS) demonstrate increased BC emissions, raising concerns about the environmental benefits of EGCS as a sustainable technology. Non-compliance with sulfur regulations also results in elevated BC emissions, underscoring the need for effective enforcement measures for the existing sulfur emission limits. Furthermore, BC EFs were found to be highly load-dependent, with ships emitting substantially more BC at lower engine loads. This is especially worrying as low engine loads are frequently used in the North Sea for navigation and strategic planning. While slow steaming is increasingly adopted for fuel efficiency at global level. These findings emphasize the significant leverage that the implementation of BC regulations and the development of BC abatement systems could represent for the maritime industry in its ambition to significantly reduce its climate impact.