Aerosol organic nitrogen across the global marine boundary layer: distribution patterns and controlling factors

Abstract. Organic nitrogen (ON) is an important yet poorly constrained component of aerosol total nitrogen (TN), particularly over remote oceans. We quantified aerosol ON in 92 total suspended particulate samples collected across approximately 160° of latitude in the marine atmospheric boundary layer (MABL) during Chinese Antarctic and Arctic expeditions (2019–2024), using a newly developed method that simultaneously determines ON and inorganic nitrogen. A significant latitudinal gradient was observed, with significantly higher ON concentrations in the Northern Hemisphere (83.3±141.4 ng m-3) than in the Southern Hemisphere (15.4±12.4 ng mm-3). Regionally, coastal East Asia recorded the highest ON levels (164.6±179.1 ng mm-3) but a lower ON/TN ratio (21.1 %), indicating strong terrestrial and anthropogenic influence. In contrast, the Arctic Ocean had lower ON concentrations (19.1±19.0 ng mm-3) but the highest ON/TN ratio (38.6 %), suggesting dominant marine biogenic sources. The Southern Ocean showed the lowest ON concentration (12.0±7.1 ng m-3) yet a relatively high ON/TN ratio (27.8 %), also pointing to oceanic origins. Near Antarctica, samples influenced by sea-ice air masses displayed markedly elevated ON and ON/TN ratios. These increases were strongly correlated with sea ice concentration and chlorophyll-a exposure, indicating enhanced biogenic emissions from sea-ice-associated ecosystems. This study offers the first direct ON measurements along a global MABL transect, revealing distinct latitudinal and regional patterns, and emphasizing the combined roles of continental inputs and marine sources. It also identifies sea-ice dynamics as a key factor influencing ON in Antarctic regions, providing crucial data for improving atmospheric and climate models.