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 ON (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, WSON remained a substantial fraction of water-soluble total nitrogen (WSTN) across all air-mass categories, although the WSON/WSTN ratio alone did not uniquely distinguish marine from anthropogenic influence. Positive matrix factorization revealed that the contribution of sea spray aerosol (SSA)-associated WSON to total WSON increased markedly with oceanic influence, accounting for 3.8 % ± 6.4 %, 14 % ± 14 %, and 34 % ± 17 % under continental, mixed, and marine conditions, respectively. The corresponding contributions to WSTN were approximately 1.6 % ± 2.1 %, 7.3 % ± 7.6 %, and 13 % ± 8.2 %, with an overall mean of 7.8 % ± 8.2 % over the sampled annual cycle. Moreover, marine productivity, assessed via air mass exposure to chlorophyll a concentrations, exhibited a strong positive correlation with SSA-associated WSON (r=0.96, p<0.001), a pattern further supported by large-scale comparison across coastal sites. These results provide multiple lines of evidence that SSA-associated WSON is an important contributor to coastal aerosol WSON under marine influence, with patterns consistent with marine-biogenic enhancement, although anthropogenic co-influences cannot be fully excluded.