British scientists to track down sulphur cap cheats by peering into the clouds

British researchers have developed a method to track down ships flouting the sulphur cap next year by watching clouds.

The study, published today in Geophysical Research Letters, was led by researchers from Imperial College London, together with University College London and the University of Oxford.

Satellite tracking was used to show the relationship between cloud properties and the sulphur content of shipping fuels, something researchers say could help monitor compliance with the International Maritime Organization’s sulphur regulations that come into force on January 1.

Emissions from ships contain several chemicals, including sulphate aerosols – small particles of sulphur and oxygen. The aerosols can act as seeds around which water droplets accumulate, causing changes in cloud properties that are visible to satellites.

This means that ships can change clouds, leaving lines – known as ship tracks (such as these pictured in the North Pacific) – in the clouds behind them as they sail.

The research team studied more than 17,000 ship tracks from satellite observations and matched them to the movements of individual ships using their onboard GPS.

The study period covered the introduction of emission control areas around the coast of North America, the North Sea, the Baltic Sea and the English Channel, which restricted sulphur in ship fuel to 0.5%, leading to fewer sulphate aerosol emissions.

The researchers found that in these areas, ship tracks nearly completely disappeared compared to before the restrictions, under similar weather conditions.

This shows that sulphate aerosols have the most significant impact on cloud formation, as opposed to other components of the ship exhaust, such as black carbon.

The result also means that a ship not in compliance with the sulphur cap regulations, by burning the current high-sulphur fuels without exhaust treatment, could be detected because it would create a measurable difference in the satellite-observed cloud properties.

Co-author Dr Tristan Smith from UCL Energy Institute, and a regular Splash contributor, said: “Currently, it is hard for regulators to know what ships are doing in the middle of the ocean. The potential for undetected non-compliance with the 2020 sulphur regulations is a real risk for shipping companies because it can create commercial advantage to those companies who do not comply.

“This study shows that science and technology are producing significant advancements in the transparency of shipping, and helping to reduce risks and unfairness for responsible operators.”

Sam Chambers

Starting out with the Informa Group in 2000 in Hong Kong, Sam Chambers became editor of Maritime Asia magazine as well as East Asia Editor for the world’s oldest newspaper, Lloyd’s List. In 2005 he pursued a freelance career and wrote for a variety of titles including taking on the role of Asia Editor at Seatrade magazine and China correspondent for Supply Chain Asia. His work has also appeared in The Economist, The New York Times, The Sunday Times and The International Herald Tribune.


  1. Very interesting:
    One must think about the influence of clouds on sunlight: Clouds reflect sunlight, so that the surface temperature of the earth will be lower. On the other hand at night, they hinder cooling down (infrared radiation). Probably the absence of clouds and sunlight on the surface of the earth will lead to higher surface temperature in the winter time, but since daylight is shorter than nighttime the final effect will be that the earth cooles down more at night than it warms up at daytime? Less clouds above oceans might lead in the winter time to lower temperatures?
    It is not written under what circumstances these ship track clouds appear, probably not in the summertime, in absence of cold layers of air, but with more daylight hours than nighttime hours? Would like to hear more about this !

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