A new study supported by the MIT Climate and Sustainability Consortium indicates that, under current legislation, switching the global fleet to ammonia fuel could cause up to 600,000 additional premature deaths each year.
However, the “Climate and Air Quality Impact of Using Ammonia as an Alternative Shipping Fuel” finds that with stronger regulations and cleaner engine technology, the switch could lead to about 66,000 fewer premature deaths than currently caused by maritime 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 decarbonize.
… said Anthony Wong, a postdoc in the MIT Center for Global Change Science and lead author of the study.
Greener, cleaner ammonia
Traditionally, ammonia is made by stripping hydrogen from natural gas and then combining it with nitrogen at extremely high temperatures. This process is often associated with a large carbon footprint. The maritime shipping industry is betting on the development of “green ammonia,” which is produced by using renewable energy to make hydrogen via electrolysis and to generate heat.
“In theory, if you are burning green ammonia in a ship engine, the carbon emissions are almost zero,” Wong says.
But even the greenest ammonia generates nitrous oxide (N2O), nitrogen oxides (NOx) when combusted, and some of the ammonia may slip out, unburnt. This nitrous oxide would escape into the atmosphere, where the greenhouse gas would remain for more than 100 years. At the same time, the nitrogen emitted as NOx and ammonia would fall to Earth, damaging fragile ecosystems. As these emissions are digested by bacteria, additional N2O is produced.
NOx and ammonia also mix with gases in the air to form fine particulate matter. A primary contributor to air pollution, fine particulate matter kills an estimated 4 million people each year.
“Saying that ammonia is a ‘clean’ fuel is a bit of an overstretch. Just because it is carbon-free doesn’t necessarily mean it is clean and good for public health,” Wong says.
The researchers aimed to comprehensively evaluate the environmental and public health impacts of transitioning the global shipping fleet to ammonia fuel. They considered two engine technologies: one that burns pure ammonia, resulting in high unburnt ammonia but low nitrogen oxides (NOx), and another that mixes ammonia with hydrogen, optimizing catalytic converter performance to reduce both NOx and unburnt ammonia. They examined three policy scenarios: current regulations, new ammonia emission limits for North America and Western Europe, and global limits on both ammonia and NOx emissions.
Using a ship track model and an air quality model, the researchers estimated the changes in pollutant emissions and their effects on particulate matter, ozone pollution, and global public health. Due to the absence of real-world data from ammonia-powered ships, they utilized experimental combustion data to inform their models.
The findings revealed that without new regulations and using pure ammonia engines, the switch could cause an additional 681,000 premature deaths annually. Cleaner engine technology, even without new regulations, could reduce premature deaths to about 80,000, and with global regulations, deaths could be further reduced by about 66,000.
The study underscored the critical need for concurrent technological advancements and policy developments to mitigate ammonia’s potential dangers while leveraging its benefits for climate and air quality. The impacts of ammonia emissions would be most severe in East Asia, where shipping volume is high, and air quality regulations are less stringent, exacerbating the formation of particulate matter.
A recent study commissioned by The Society for Gas as a Marine Fuel (SGMF), had also highlighted that given ammonia’s toxic nature, ensuring safety in its handling, both onboard ships and during bunkering operations, is crucial. While existing infrastructure for ammonia transport and storage exists, additional safety measures tailored to marine applications are necessary, the report pointed out.
