Marine-Derived Water-Soluble Organic Nitrogen in Coastal Air: Influence of Ocean Productivity on Atmospheric Nitrogen Cycling

Abstract. Organic nitrogen (ON) deposition from aerosols plays a crucial role in oceanic ecosystems; however, the influence of marine biogenic activity on atmospheric ON remains poorly understood. Here, we investigate the contribution of the marine biosphere to water-soluble organic nitrogen (WSON) in coastal aerosols based on particulate matter samples collected in Bangkok, Thailand, from January 2016 to January 2017. Concentrations of WSON and water-soluble inorganic nitrogen (WSIN, including NO₃⁻ and NH₄⁺) were analyzed and compared across days classified by air mass origin over land as marine-, mixed-, or continental-influenced. Air masses of marine origin showed significantly lower WSON and WSIN concentrations than those from mixed and continental origins. Nevertheless, the relative proportion of WSON in water-soluble total nitrogen remained consistent, implying a persistent marine source. Positive matrix factorization revealed that the contribution of sea spray aerosol (SSA)-derived WSON increased markedly with oceanic influence, accounting for 3.8 % ± 6.4 %, 14 % ± 14 %, and 34 % ± 17 % under continental, mixed, and marine conditions, respectively. Moreover, marine productivity, assessed via air mass exposure to chlorophyll a concentrations (AEC), exhibited a strong positive correlation with SSA-derived WSON (r = 0.96, p < 0.001), a finding supported by large-scale reanalysis. These results provide direct evidence that marine organic aerosols represent a major source of WSON in coastal regions globally, with important implications for atmospheric nitrogen cycling and climate feedback processes.