A Clean Alternative or a New Environmental Challenge? A Perspective on Downstream Emissions and Environmental...

The use of ammonia (NH₃) as a carbon-free fuel in non-road engines, e.g. for maritime traffic or agricultural machines, emerges as an option to reduce carbon dioxide (CO₂) emissions. However, the environmental consequences of large-scale NH₃ combustion extend beyond CO₂ mitigation and remain insufficiently explored. This perspective briefly discusses the benefits and drawbacks of different NH₃ combustion technologies and highlights key challenges, including combustion byproduct formation, incomplete NH₃ conversion, secondary aerosol formation, and potential toxicological impacts for NH₃ with diesel pilot fuel injection. NH₃ combustion may introduce reactive nitrogen species and organic byproducts that affect atmospheric chemistry, air quality, and public health. The interaction of NH₃-derived emissions with biogenic and anthropogenic pollutants adds complexity to their environmental fate. Given these uncertainties, early stage assessments of emissions, atmospheric transformations, and their downstream effects are mandatory. By integrating combustion science, atmospheric chemistry, and toxicology, a proactive approach is suggested to identify and mitigate unintended consequences before NH₃ becomes a dominant energy carrier.