The gas nitrogen monoxide (NO) belongs to the group of nitrogen oxides, infamous as toxic emissions in urban agglomerations. But NO is also produced in nature and plays a role in the nitrogen cycle, which is essential for most organisms. However, in the ocean, Earth’s largest ecosystem, NO levels were not known. Researchers from the GEOMAR Helmholtz Centre for Ocean Research Kiel and the Collaborative Research Center have now published new NO concentration data from the eastern tropical South Pacific Ocean in Deep Sea Research Part II, for which a newly developed measuring method was used for the first time.