MIT study warns on health risks associated with switch to ammonia fuel

A new study led by the Massachusetts Institute of Technology (MIT) has warned over the health risks from shipping’s switch to using ammonia as its future fuel. 

Ammonia combustion generates nitrous oxide (N2O), a greenhouse gas that is about 300 times more potent than carbon dioxide, the study points out. It also emits nitrogen in the form of nitrogen oxides (NO and NO2, referred to as NOx), and unburnt ammonia may slip out, which eventually forms fine particulate matter in the atmosphere.

The study indicates that, under current legislation, switching the global fleet to ammonia fuel could cause up to about 600,000 additional premature deaths each year. However, with stronger regulations and cleaner engine technology, the switch could lead to about 66,000 fewer premature deaths than currently caused by shipping emissions, with far less impact on 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 decarbonise,” said Anthony Wong, a postdoc in the MIT Center for Global Change Science and lead author of the study. Researchers from Imperial College London, the University of Orléans, and the Hong Kong University of Science and Technology also participated in the study.

The researchers considered two ship engines. The first burns pure ammonia, which generates higher levels of unburnt ammonia but emits fewer nitrogen oxides. The second engine technology involves mixing ammonia with hydrogen to improve combustion and optimise the performance of a catalytic converter, which controls both nitrogen oxides and unburnt ammonia pollution.

They also considered three policy scenarios: current regulations, which only limit NOx emissions in some parts of the world; a scenario that adds ammonia emission limits over North America and Western Europe; and a scenario that adds global limits on ammonia and NOx emissions.

The researchers used a ship track model to calculate how pollutant emissions change under each scenario and then fed the results into an air quality model. The air quality model calculated the impact of ship emissions on particulate matter and ozone pollution. Finally, they estimated the effects on global public health.

In the end, they found that with no new regulations and ship engines that burn pure ammonia, switching the entire fleet would cause 681,000 additional premature deaths each year.