Latitudinal distributions of organic nitrogen and organic carbon in marine biologically influenced aerosols over the western North Pacific in summer

Latitudinal distributions of organic nitrogen (ON) and organic carbon (OC) as well as isotopic ratios of total nitrogen (TN) and total carbon (TC) were measured in marine aerosols collected in the western North Pacific in summer 2008. Increased concentrations of methanesulfonic acid (MSA) and diethylammonium (DEA+) at 40-44N and subtropical regions (10-20N), together with averaged satellite chlorophyll a data and five-day back trajectory, suggest significant influences of marine biological activities on aerosols in these regions. In the marine biologically influenced aerosols, ON exhibited increased concentrations up to 260 ngN m-3. We found that water-insoluble organic nitrogen (WION) was the most abundant N in the marine aerosols, which accounted for 67±15% of total aerosol N. In particular, the average WION/ON ratio was as high as 0.93±0.07 at 40-44N. These results suggest that marine biological sources significantly contributed to ON, a majority of which is composed of water-insoluble fractions in the study region. The stable carbon isotopic ratios (δ13C) showed higher values (from -22‰ to -20‰) when ON/OC ratios increased from 0.15 to 0.35. The results clearly show an enrichment of nitrogen in organic aerosols originated from the oceanic region with high biological productivity and indicate preferential transfer of nitrogen-containing compounds from the sea surface to marine atmosphere. Furthermore, both WION concentrations and WION/WIOC ratios showed positive correlations with local wind speeds, suggesting that ON contributes significantly as a nutrient-affiliated element to primary marine organic aerosols over the study region. We will discuss possible chemical properties of WION including proteins and gel-like particles, and potential processes for primary and secondary production of aerosol ON.