Continental pollutants modulate organic nitrogen and light absorption of marine organic aerosols over East Asian marginal seas

Abstract. Organic nitrogen (ON) in marine aerosols is not only an important fraction of atmospheric nitrogen deposition but also a vital contributor to light-absorbing organic aerosols. However, ON abundance, sources, or its influence on organic aerosol absorption remain unclear in marine atmosphere. Here, shipboard observations were conducted in spring, summer, and autumn over the Yellow Sea and Bohai Sea (YBS) to understand the spatiotemporal distributions and sources of aerosol ON over East Asian marginal seas. Aerosol ON was 0.35 ± 0.25 μgN/m³, accounting for 4 %–60 % of total nitrogen in marine aerosols. Concentrations of ON were the highest in autumn due to severe impacts of anthropogenic pollutants, followed by those in spring and summer. Anthropogenic secondary pollutants (aged biomass burning and secondary nitrate formation) were the most important sources of aerosol ON, contributing 36 %–76 % of ON, 46 %–83 % of water-soluble ON, and 39 %–89 % of water-insoluble ON. In spring, 55 % of ON, 45 % of water-soluble ON, and 54 % of water-insoluble ON were attributed to dust, and its contribution increased to >80 % during a dust episode. In summer, marine sources associated with biological activity were important for aerosol ON formation. Nitrogen-containing organic compounds played vital roles in regulating light absorption by organic aerosols over the YBS. Elevated organic aerosol absorption was not only attributed to higher ON concentrations, but also related to increased absorption capability at higher ON/OC ratios. Our results highlight transported continental ON drove the light absorption by marine organic aerosols over marginal seas.