UK-based researchers have released a study claiming that ships breaking the sulphur cap from January 2020 will be trackable by looking at the content of clouds.
The study, from Geophysical Research Letters, was led by researchers from Imperial College London, together with University College London and the University of Oxford.
Satellite tracking showed a relationship between cloud properties and the sulphur content of shipping fuels. The study said that this could help monitor compliance/non-compliance with the 0.50% sulphur cap, which comes into effect on January 1st.
The study said that emissions from ships contained several chemicals, including sulphate aerosols. The aerosols can act as seeds, around which water droplets accumulate, causing changes in cloud properties that are visible to satellites.
Ships can leave lines known as ship tracks 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 data obtained from 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, the study said, showed that sulphate aerosols had the most significant impact on cloud formation, as opposed to other components of the ship exhaust, such as black carbon.
The result also meant that a ship which was not complying with the sulphur cap regulations would be detectable because it would create a measurable difference in the satellite-observed cloud properties.