Without enhanced regulations, the utilization of ammonia as fuel in ship engines has the potential to significantly impact air quality, leading to an increase of over 600,000 premature deaths annually, as indicated by recent research.
As massive container ships traverse the oceans resembling city blocks to transport goods, their large diesel engines emit substantial amounts of air pollutants that contribute to climate change and have negative effects on human health. It has been estimated that maritime shipping is responsible for nearly 3% of global carbon dioxide emissions, with associated impacts on air quality causing approximately 100,000 premature deaths each year.
Reducing these detrimental effects by decarbonizing shipping is a key objective of the International Maritime Organization, a U.N. regulatory agency overseeing maritime transport. One proposed solution is transitioning the global fleet from traditional fossil fuels to sustainable alternatives like ammonia, which could be close to carbon-neutral considering its production and usage.
However, a recent study conducted by a team of researchers from MIT and other institutions highlights the potential risks of burning ammonia as maritime fuel, including worsened air quality and significant public health consequences, unless accompanied by stricter emissions regulations.
Ammonia combustion produces nitrous oxide (N2O), a potent greenhouse gas around 300 times more powerful than carbon dioxide. It also emits nitrogen in the form of nitrogen oxides (NO and NO2, collectively known as NOx), and unburned ammonia may escape into the atmosphere, eventually forming fine particulate matter which can be inhaled into the lungs, leading to health issues such as heart attacks, strokes, and asthma.
The study reveals that under current legislation, switching the global fleet to ammonia fuel could result in up to approximately 600,000 additional premature deaths yearly. Nevertheless, with more stringent regulations and cleaner engine technology, this shift could potentially prevent around 66,000 premature deaths compared to the current toll caused by maritime shipping emissions, with significantly less impact on global warming.
“Not all climate solutions are equal in their outcomes. There is usually some trade-off involved. We need to take a comprehensive approach and consider both the costs and benefits of various climate solutions, rather than solely focusing on their decarbonization potential,” says Anthony Wong, a postdoc at the MIT Center for Global Change Science and the study’s lead author.
The study’s co-authors include Noelle Selin, an MIT professor, Sebastian Eastham from Imperial College London, Christine Mounaïm-Rouselle from the University of Orléans, Yiqi Zhang from the Hong Kong University of Science and Technology, and Florian Allroggen from MIT. The research has been published in Environmental Research Letters.
Eco-Friendly Ammonia Production
Typically, ammonia is produced by extracting hydrogen from natural gas and then combining it with nitrogen at extremely high temperatures, a process associated with a considerable carbon footprint. The maritime industry is banking on the development of “green ammonia,” which is generated by using renewable energy to produce hydrogen through electrolysis and heat.
“In theory, if ships burn green ammonia, carbon emissions are nearly eliminated,” notes Wong.
Nevertheless, even the most environmentally friendly ammonia releases nitrous oxide (N2O), nitrogen oxides (NOx) upon combustion, and some unburned ammonia could escape into the atmosphere. Nitrous oxide remains a greenhouse gas for over 100 years once released. Additionally, the nitrogen emitted as NOx and ammonia settles on the Earth, damaging fragile ecosystems. Bacteria processing these emissions further produce additional N2O.
NOx and ammonia combine with atmospheric gases to create fine particulate matter, which is a key contributor to air pollution and causes an estimated 4 million deaths annually.
“Referring to ammonia as a ‘clean’ fuel may be stretching the truth a bit. Just because it lacks carbon emissions doesn’t automatically mean it promotes cleanliness and public health,” explains Wong.
A Comprehensive Model
The researchers aimed to provide a holistic view, encompassing the environmental and public health implications of transitioning the global fleet to ammonia fuel. To achieve this, they devised various scenarios to gauge how pollutant impacts evolve based on specific technological and policy assumptions.
Technologically, they examined two ship engine options. The first burns pure ammonia, resulting in higher unburned ammonia levels but lower nitrogen oxide emissions. The second engine type involves blending ammonia with hydrogen to enhance combustion and optimize the catalytic converter’s efficiency, which manages both nitrogen oxides and unburned ammonia emissions.
They also considered three policy scenarios: existing regulations that solely restrict NOx emissions in specific regions, an alternative scenario adding ammonia emission limits in North America and Western Europe, and a scenario imposing global restrictions on ammonia and NOx emissions.
The researchers utilized a ship track model to evaluate how pollutant emissions change under each scenario, feeding the outcomes into an air quality model. This model calculated the impact of ship emissions on particulate matter and ozone pollution, eventually estimating the implications for global public health.
A significant challenge arose from the absence of real-world data, as no ammonia-powered ships are currently operational. Hence, the researchers leveraged experimental ammonia combustion data obtained from collaborators to develop their model.
“We had to devise creative strategies to make that data valuable and relevant to both technological and regulatory contexts,” Wong adds.
Diverse Outcomes
Ultimately, their analysis revealed that in a scenario devoid of new regulations and reliant on ship engines burning pure ammonia, transitioning the entire fleet could lead to an extra 681,000 premature deaths annually.
“While a no-regulation scenario may not be practical, it serves as a crucial signal of how hazardous ammonia emissions could be. Unlike NOx, ammonia emissions from shipping currently lack regulatory controls,” Wong underscores.
However, even without new regulations, adopting cleaner engine technology could reduce premature deaths to about 80,000, representing 20,000 fewer deaths attributable to maritime shipping emissions. With stricter global regulations and cleaner engine technologies, deaths caused by air pollution from shipping could potentially decrease by about 66,000.
“The study results underscore the importance of aligning policies with new technologies,” Selin emphasizes. “Ammonia’s potential benefits for both climate and air quality can only be realized if regulations address the entire spectrum of impacts, encompassing both climate change and air quality concerns.”
The impacts of ammonia on air quality would not be uniformly distributed worldwide and addressing them comprehensively would necessitate coordinated strategies across diverse contexts. The majority of premature deaths would likely occur in East Asia due to less stringent air quality regulations in the region. Additionally, higher existing pollution levels in East Asia contribute to increased particulate matter formation from ammonia emissions. Moreover, the volume of shipping activity in East Asia surpasses that in other regions, exacerbating these adverse effects.
In the future, the researchers aspire to refine their analysis further. They aim to leverage these findings to encourage the maritime industry to share engine data that could enhance evaluations of air quality and climate impacts. Furthermore, they intend to raise awareness among policymakers about the critical need to update shipping emission regulations.
This research received funding from the MIT Climate and Sustainability Consortium.
