Marine nitrogen fixation as a possible source of atmospheric water-soluble organic nitrogen aerosols in the subtropical North Pacific

Abstract

Abstract. Water-soluble organic nitrogen (WSON) in marine atmospheric aerosols affect the water solubility, acidity, and light-absorbing properties of aerosol particles, which are important parameters in assessing both the climate impact and the biogeochemical cycling of bioelements. Size-segregated aerosol and surface seawater (SSW) samples were simultaneously collected over the subtropical North Pacific to investigate the origin of WSON in the marine atmosphere. The fine-mode WSON concentration (7.5 ± 6.6 ngN m−3) at 200–240∘ E along 23∘ N, defined as the eastern North Pacific (ENP), was significantly higher than that (2.4 ± 1.9 ngN m−3) at 135–200∘ E, defined as the western North Pacific (WNP). Analysis of the stable carbon isotope ratio of water-soluble organic carbon (WSOC; δ13CWSOC) together with backward trajectory indicated that most of the observed WSON in the fine particles in the ENP originated from the ocean surface. We found positive relations among nitrogen-fixation rate, dissolved organic nitrogen (DON) in SSW, and the WSON concentrations. The result suggests that reactive nitrogen (DON and ammonium), produced and exuded by nitrogen-fixing microorganisms in SSW, contributed to the formation of WSON aerosols. This study provides new insights into the role of ocean-derived reactive nitrogen aerosols associated with marine microbial activity.

Marine aerosol feedback on biogeochemical cycles and the climate in the Anthropocene: lessons learned from the Pacific Ocean

“…Furthermore, possible effects of nitrogen xation, which converts dinitrogen (N 2 ) gas to ammonia (NH 3 ), on atmospheric emissions of reactive N (including organic N) have been investigated. 54 The atmospheric emission uxes of organic N or NH 3 (or ammonium) from the sea surface are important in terms of estimating atmospheric deposition uxes of anthropogenic reactive N. 55 Reactive gas species (e.g., VOCs or reactive N), which are photochemically produced at the air-sea interface, have been suggested to be involved in new particle formation, although large uncertainties exist in their amount. 56 It is important to elucidate the emission ux of the carbon mass of primary emissions by SSAs as well as that of SOAs and to reveal their importance relative to the number and mass of sea salt.…”