Atmospheric water-soluble organic nitrogen (WSON) over marine environments: A global perspective

Abstract

To obtain a comprehensive picture of the spatial distribution of water-soluble organic nitrogen (WSON) in marine aerosols, samples were collected during research cruises in the tropical and southern Atlantic Ocean and also in the southern Indian Ocean (Amsterdam Island) for a 1-year period (2005). Samples were analyzed for both organic and inorganic forms of nitrogen, and the factors controlling their levels were examined. Fine-mode WSON was found to play a significant role in the remote marine atmosphere with enhanced biogenic activity, with concentrations of WSON (11.3 ± 3.3 nmol Nm -3) accounting for about 84 % of the total dissolved nitrogen (TDN). Such concentrations are similar to those observed in the polluted marine atmosphere of the eastern Mediterranean (11.6 ± 14.0 nmol N m -3). Anthropogenic activities were found to be an important source of atmospheric WSON as evidenced by the levels in the Northern Hemisphere (NH) being 10 times higher than in the remote Southern Hemisphere (SH). Furthermore, the higher contribution of fine-mode WSON to TDN (51%) in the SH, compared to the NH (13%), underlines the important role of organic nitrogen in remote marine areas. Finally, there was a strong association of WSON with dust in coarse-mode aerosols in the NH.