Nitrogen Stable Isotopes Track Ammonia Emission Sources and Ammonium Aerosol Formation Processes in the Marine Boundary Layer

Ammonia is the most important basic gas in the atmosphere, influencing aerosol formation and acidity, with important consequences for climate. Human activities have greatly increased atmospheric ammonia emissions, making it difficult to isolate natural sources. The ocean is the largest natural emitter of ammonia, but concentrations in the pristine marine atmosphere are too low for direct measurement. In this study, Altieri et al. used nitrogen stable isotopes in seawater ammonium and marine aerosol ammonium to identify the isotopic signature of ammonia released from the ocean. The results show that ocean-derived ammonia can be distinguished from seabird-derived ammonia in aerosols and provide new constraints on aerosol formation pathways. These findings improve our understanding of natural aerosol processes and their role in climate change.

Reference: Altieri, K. E., Smith, S., Fawcett, S. E., et al. (2026). Nitrogen stable isotopes track ammonia emission sources and ammonium aerosol formation processes in the marine boundary layer. Geophys. Res. Lett., 12, e2025GL119557. https://doi.org/10.1029/2025GL119557