Ship exhaust emissions change clouds’ behaviour, study finds

Newly published research from The University of Manchester shows that some ships in the open ocean were emitting large amounts of sulphates from traces of sulphur in the fuel, with a strong potential to alter clouds’ behaviour and pollute coastal areas.

The main concerns are particulates, made of a mixture of soot and sulphates, which have long been known to alter the behaviour of clouds in the open ocean, creating lines of brighter clouds behind ships that can been seen from space (ship tracks), similar to the contrails often seen behind aeroplanes.

The brighter clouds are partly caused by exhaust plumes containing pollutants from burning fossil fuels to power the ships. Scientists and shipping organisations are now studying the impact of increased regulations on the environmental cost of global shipping.

Now, the UKRI-funded ACRUISE (Atmospheric Composition and Radiative forcing changes due to UN International Ship Emissions regulations) project is designed to study the change this has, both on emissions and its impact on the environment. The project was designed to run in two phases, to deliver a ‘before and after’ picture.

These results are quite remarkable. Traditionally, ship fuel has been one of the dirtiest forms of fossil fuels in use, but these results give an insight into what kind of a change the new regulations can have. It will be very interesting to see what differences we will find in the second phase of the experiment.

states Dr James Allan.

The results represent the ‘before’ measurements of the particulates from ocean-going cargo ships. While work has been published previously on ship emissions, these have tended to be in laboratory test rigs, which may not represent ‘real’ emissions, or in territorial waters or ports, where controls are already established.

The Manchester scientists used the UK Facility for Airborne Atmospheric Measurement (FAAM) Bae-146 large research aircraft to fly directly through the exhaust plumes of cargo ships in the busy Atlantic shipping lanes off the Portuguese coast in 2019, before the new controls were enacted.

The ACRUISE project is currently ongoing, and in 2021, the team will return to repeat the measurements, to assess how much of an impact the new controls have made. These will be combined with satellite data and atmospheric models to determine how much of a change this has made to air quality and climate.

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