Study Finds Major Drop in Ship Sulfur Emissions Following IMO Regulations

An academic team led by researchers at the UK’s National Centre for Atmospheric Science completed a first in-depth study looking at sulfur emissions at sea and found “fairly good compliance” with the IMO regulations introduced in 2020. The group looked at compliance both in the European Sulfur Emission Control Areas (SECAs) and ships in the open ocean.

The team found that the average sulfur content in ship fuel dropped nearly tenfold in open ocean areas following the International Maritime Organization’s 2020 regulation, which capped sulfur content in marine fuel at 0.5 percent. Before the change, many ships exceeded the previous 3.5 percent limit. After 2020, they reported that only a small number of ships were found to breach the new standard.

In European Sulfur Emission Control Areas (SECAs), such as the English Channel and the Port of Tyne, sulfur levels were even lower. They said it was well below the stricter 0.1 percent limit, and interestingly, ports outside these zones, like Valencia in Spain, also showed low sulfur levels. They said this was likely due to the European Union’s rules, which also require cleaner fuel when ships are docked for extended periods.

The research, published in Environmental Science: Atmospheres, used aircraft and ground-based instruments to measure sulfur dioxide and nitrogen oxides emitted by ships in the North-East Atlantic and European coastal waters between 2019 and 2023. They noted that this was the first study to use aircraft-based measurements and predictions from the Ship Traffic Emission Assessment Model (STEAM3) to assess ship emissions outside of sulfur control zones since the 2020 regulation came into effect.

The use of aircraft was a critical component, as the regulations are different in ports and inland waterways compared to the open ocean. The authors said that an aircraft was the only way to get the open ocean measurements.

While the findings support the widely held view that ships now emit around seven times less sulfur than before the rule change, they noted that compliance is far from universal.

“It’s a big reduction, largely in line with the change in regulations,” said Professor James Lee, an atmospheric chemist at NCAS and the University of York.

However, the research found that in the open ocean, five ships out of 78 breached the 0.5 percent sulfur content limit in 2021 and 2022. The researchers noted that their project had a limited sample size, which made it difficult to draw any conclusions about what might cause a ship to breach the limit, e.g. its age or its tonnage.

“That’s quite a substantial proportion of the observed fleet,” noted Professor Hugh Coe, atmospheric composition research scientist at NCAS and the University of Manchester. “While it’s reasonable to assume the fleet’s average is below the 0.5 percent limit, there could be a significant number of outlier ships breaching that limit, potentially having a large effect on local air quality.”

The research said that more measurements would be needed to investigate the cause of the outlier ships. They also recommended that policymakers keep a careful eye on the ships and the challenges to introduce alternative fuels. They said it is important to make sure that any change that might be beneficial from a carbon reduction point of view does not have unexpected and adverse air quality implications.