Climate Impact of Direct and Indirect N<sub>2</sub>O Emissions from the Ammonia Marine Fuel Value Chain
Sofia Esquivel‐Elizondo, Blake Walkowiak, Stavroula S. Sartzetakis, Brian Buma
Abstract
High Resolution Image Download MS PowerPoint Slide Ammonia (NH 3 ) emerges as a near-zero-carbon shipping fuel, but its value chain can emit noncarbon greenhouse gases (GHGs) like nitrous oxide (N 2 O) and pollutants, such as NH 3 and nitrogen oxides (NO x ). N 2 O, with 273 times the global warming potential of carbon dioxide (CO 2 ), is also indirectly emitted through transformations of reactive nitrogen (N r ) species, like NH 3 and NO x, in natural environments. Understanding ammonia’s climate impact is crucial for evaluating its efficacy as a fossil fuel alternative. We present a functional model to quantify the climate impact of renewable-based (e-ammonia) and natural-gas-based (blue and gray) ammonia, focusing on direct and indirect N 2 O emissions. The model incorporates N r emissions─NH 3, NO x, and N 2 O─across the value chain under “low”, “medium”, and “high” emissions scenarios, along with production and pilot fuel GHG emissions. Results show that e-ammonia’s climate benefit depends on well-to-wake N r emissions and natural processes that control relevant nitrogen to indirect N 2 O (N-to-N 2 O i ) conversion pathways. In a low emissions scenario, its CO 2 -equivalent intensity is 68–80% lower than fuel oil, assuming 1–10% N-to-N 2 O i conversion. In a high emissions scenario, this benefit drops to 11–23% for 1–2% N-to-N 2 O i conversion, and at 5–10% N-to-N 2 O i conversion, e-ammonia’s impact exceeds fuel oil by >24%. Blue ammonia could bring ∼30% climate benefit compared to fuel oil, but only in a low emissions scenario with 1–2% N-to-N 2 O i conversion. While more data on emissions and N-to-N 2 O i conversion are needed, minimizing NH 3, NO x, and N 2 O emissions is crucial to maximizing ammonia’s climate benefits.