A recent study by Massachusetts Institute of Technology shows that replacing diesel fuel with ammonia in marine vessels would significantly reduce current emissions, but without more stringent regulations on ammonia emissions would theoretically prove even more hazardous to health.
Shipping is responsible for 3% of global greenhouse gas emissions. Major shipping companies such as Maersk have been moving the industry toward more sustainable alternatives such as ammonia, made by stripping hydrogen from natural gas and combining it with nitrogen at extremely high temperatures. Green ammonia, produced with renewable energy, would have almost no emissions.
In December, Maersk announced that it had ordered up to 10 very large ammonia carriers (VLACs) from Hyundai Samho Heavy Industries. The announcement said the Korean-built vessels will have a capacity of 93,000 cubic meters and that the first four vessels would be delivered from late 2026.
However, the announcement said Maersk would wait for “regulatory and customer” support before making a decision to install ammonia-capable engines.
Now MIT researchers report that new regulations are required to make the transition to ammonia a net positive for the environment. Ammonia combustion generates nitrous oxide (N2O), a greenhouse gas (GHG) that is about 300 times more potent than carbon dioxide. It also emits nitrogen in the form of nitrogen oxides (NO and NO2, referred to as NOx). According to the report, this NOx would escape into the atmosphere, where it would remain for more than 100 years. Nitrous oxide and ammonia would fall to Earth, damaging fragile ecosystems. As these emissions are digested by bacteria, additional N2O is produced.
The researchers also postulated that unburnt ammonia particles could slip out forming fine matter in the atmosphere that could be inhaled and create health problems.
Researchers’ models indicated that burning pure ammonia in ships could lead to 600,000 more premature deaths per year.
However, the team said that if ammonia was mixed with hydrogen it would improve combustion and optimize the performance of a catalytic converter, which controls both nitrogen oxides and unburnt ammonia pollution. And implementing cleaner engine technology in tandem with strengthening regulations on ammonia emissions–currently unregulated in many parts of the world–could result in 66,000 fewer premature deaths than currently caused by maritime shipping emissions, with far less contribution to global warming.
“Not all climate solutions are created equal. There is almost always some price to pay. We have to take a more holistic approach and consider all the costs and benefits of different climate solutions, rather than just their potential to decarbonize,” says Anthony Wong, a postdoc in the MIT Center for Global Change Science and lead author of the study.
