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.”