Ammonia may be a nearly carbon-free marine fuel, but without new emissions regulations, its impact on air quality could greatly affect human health.

A new study by MIT scientists shows that burning ammonia in ship engines could contribute to ozone pollution while having serious impacts on air quality. When city-block-sized container ships move cargo across oceans, large diesel engines emit large amounts of air pollutants that contribute to climate change and affect human health. The shipping industry is estimated to account for about 3% of global carbon dioxide emissions. Also, the industry’s negative impact on air quality causes about 100,000 premature deaths each year.

The International Maritime Organization is the United Nations agency that regulates maritime transport. It aims to reduce these harmful effects by decarbonizing shipping. One potential solution is to switch the global fleet from fossil fuels to sustainable fuels. Such as ammonia, which could be nearly carbon-neutral given its production and use.

However, in a new study, an interdisciplinary team of researchers from MIT. Elsewhere warns that burning ammonia as a marine fuel could worsen air quality and lead to devastating public health impacts unless it’s adopted in conjunction with tightened emissions regulations.

How Does It Happen?

Ammonia combustion produces nitrous oxide (N2O), a greenhouse gas that’s about 300 times more potent than carbon dioxide. It also emits nitrogen in the form of nitrogen oxides (NO and NO2, or NOx), and unburned ammonia can escape, eventually forming fine particulate matter in the atmosphere. These small particles can be inhaled deep into the lungs, causing health problems such as heart disease, stroke, and asthma.

The new study suggests that switching the global fleet to ammonia fuel could cause about 600,000 premature deaths yearly under current legislation. However, with stricter regulations and cleaner engine technology. Such a switch could result in about 66,000 fewer deaths than currently caused by shipping emissions and with far less impact on global warming.

“Not all climate solutions are equal, and we have to take a more holistic approach and consider all the costs and benefits of different climate solutions, not just their ability to remove carbon,” says Anthony Wong, a postdoctoral researcher at the MIT Climate Change Center and the study’s lead author.

Its co-authors include Noelle Selin, a professor at MIT’s Institute for Data, Systems, and Society and the Department of Earth, Atmospheric, and Planetary Sciences (EAPS); Sebastian Eastham, a former principal research scientist and now a senior lecturer at Imperial College London; Christine Monem Roussel, a professor at the University of Orleans, France; Weiqi Zhang, a researcher at the Hong Kong University of Science and Technology; and Florian, a research scientist in MIT’s Department of Aeronautics and Astronautics. Allrögen. The study was published this week in Environmental Research Letters.

Ammonia Is Greener And Cleaner.

Traditionally, ammonia is made by removing 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 shipping industry is betting on the development of “green ammonia.” Which is produced by using renewable energy to make hydrogen through electrolysis and heat.

“In theory, if green ammonia is burned in a ship’s engine, carbon emissions are almost zero,” Huang said.

However, even the most environmentally friendly ammonia produces nitrous oxide (N2O) and nitrogen oxides (NOx). When it burns, some ammonia may escape without burning. This nitrous oxide escapes into the atmosphere, where it will remain as a greenhouse gas for more than 100 years. Meanwhile, the nitrogen released in the form of nitrogen oxides and ammonia falls to the ground, damaging fragile ecosystems. When bacteria digest these emissions, additional nitrous oxide is produced.

Nitrogen oxides and ammonia also mix with gases in the air to form fine particles. Fine particulate matter is a major cause of air pollution. Causing 10,000 deaths with an estimated 10,000 deaths400 million tons yearly.

“To say ammonia is a ‘clean’ fuel is a bit of an exaggeration,” Wong said. “Just because it’s carbon neutral doesn’t necessarily mean it’s clean and good for public health.”

Multifaceted Model

The researchers wanted to paint a full picture of the environmental and public health impacts of switching to ammonia fuel for the global fleet. To do so, they designed scenarios to measure how the impact of pollutants would change under certain technology and policy assumptions.

From a technical perspective, they are considered engines for ships. The first burns pure ammonia, producing higher levels of unburned ammonia but emitting less nitrogen oxides. The second engine technology involves mixing ammonia with hydrogen to improve combustion and boost catalytic converter performance. Thereby controlling nitrogen oxide and unburned ammonia pollution.

They also considered three policy scenarios. Current regulations limit nitrogen oxide emissions only in certain parts of the world. This scenario increases ammonia emission limits in North America and Western Europe. It also increases global limits on ammonia and nitrogen oxide emissions.

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

One of the biggest challenges was the lack of real-world data. Since there are currently no ammonia-powered ships sailing at sea. Instead, the researchers relied on experimental ammonia combustion data provided by collaborators to build their model.

“We had to come up with some clever ways to make this data useful and informative for both the technical and regulatory scenarios,” he said.

One set of results

Ultimately, they found that replacing the entire fleet would lead to 681,000 premature deaths per year without new regulations and marine engines burning pure ammonia.

“While the scenario without new regulations is unlikely to be realistic, it serves as a good warning of the dangers of ammonia emissions, “Unlike nitrogen oxides, ammonia emissions from shipping are currently unregulated,” Huang said.

However, even without new regulations, the use of clean engine technology could reduce premature deaths to about 80,000, about 20,000 fewer than those currently caused by shipping emissions. With stricter global regulations and cleaner engine technology, deaths from air pollution from shipping could fall by 66,000.

“The results of this study show the importance of developing policies in parallel with new technologies,” said Selin. “Ammonia in shipping has the potential to be beneficial for climate and air quality, but this requires regulations to be designed to address the full range of potential impacts, including climate and air quality. ”

Future / Impact of Ammonia

The impacts of ammonia on air quality do not affect the same areas around the world. Addressing them adequately requires coordinated strategies across settings. Most premature deaths occur in East Asia, where air quality regulations are less stringent. Current high levels of air pollution lead to more particulate matter from ammonia emissions. Additionally, shipping volumes in East Asia are much greater than anywhere else on Earth, exacerbating these negative effects.

In the future, the researchers hope to continue to improve their analysis. They hope to use these findings as a starting point to get the marine industry to share engine data so that air quality and climate impacts can be better assessed. They also aim to educate policymakers on the importance and urgency of updating shipping emissions regulations.