Isotopic compositions and biogenic tracer compounds of organic carbon and organic nitrogen in marine aerosols over the eastern equatorial Pacific

Submicrometer particles were collected with sampling intervals of ~24 hours over the eastern equatorial Pacific during the TORERO/KA-12-01 cruise in February 2012. Water-soluble organic fraction of total carbon (TC) was ~40±16% during the cruise. To investigate the marine and terrestrial source contributions to aerosol carbon and nitrogen, stable carbon and nitrogen isotopic compositions were determined. The average stable carbon isotope ratios of water-soluble organic carbon (δ13C_WSOC) (-19.8±2.0‰) were generally higher than those of TC (δ13C_TC) (-22.2±1.9‰). These values are close to typical values of δ13C for organic carbon (OC) ranging from -22‰ to -20‰ in sea water in tropical oceans, suggesting an enrichment of marine biological products in organic carbon aerosols. In particular, the δ13C_WSOC showed higher values over upwelling areas, which is attributable to planktonic tissues more enriched in δ13C. The δ13C analysis indicates that marine-derived carbon accounted for 93±26% of WSOC. WSOC and oxidation products of isoprene exhibited higher loadings over the coastal region. For aerosol nitrogen, we found that water-insoluble organic nitrogen (WION) was the most abundant (70±13% of the total aerosol nitrogen) at 95-134W, where nitrogen isotope ratios of WION (δ15N_WION) were within a typical range of δ15N in sea water in the eastern equatorial Pacific. The result indicates an enrichment of marine biologically-derived ON in aerosols in the oceanic region. We will also discuss potential processes for primary and secondary production of aerosol OC and ON in this region.