Water-soluble organic nitrogen (WSON) in coastal aerosols is critical for atmospheric chemistry and climate processes. This Bangkok study found sea-spray aerosol (SSA) is an important contributor to coastal aerosol WSON under marine air, its contribution surging from 3.8 % (continental) to 34 %. SSA-associated WSON strongly correlated (r=0.96) with trajectory-based air-mass exposure to chlorophyll-a, which is consistent with marine-biogenic enhancement.