Contribution of dissolved organic matter to submicron water-soluble organic aerosols in the marine boundary layer over the eastern equatorial Pacific
Journal Article
Abstract. Stable carbon isotopic compositions of water-soluble organic carbon (WSOC) and organic molecular markers were measured to investigate the relative contributions of the sea-surface sources to the water-soluble fraction of submicron organic aerosols collected over the eastern equatorial Pacific during the Tropical Ocean tRoposphere Exchange of Reactive halogens and Oxygenated VOCs (TORERO)/KA-12-01 cruise. On average, the water-soluble organic fraction of the total carbon (TC) mass in submicron aerosols was ~ 30–35 % in the open oceans, whereas it was ~ 60 % in the coastal oceans. The average stable carbon isotope ratio of WSOC (δ13CWSOC) was −19.8 ± 2.0 ‰, which was systematically higher than that of TC (δ13CTC) (−21.8 ± 1.4 ‰). We found that in both coastal and open oceans, the δ13CWSOC was close to the typical values of δ13C for dissolved organic carbon (DOC), ranging from −22 ‰ to −20 ‰ in surface seawater of tropical Pacific oceans. This suggests an enrichment of marine biological products in WSOC aerosols in the study region regardless of the oceanic area. In particular, enhanced levels of WSOC and biogenic organic marker compounds together with high values of WSOC/TC (~ 60 %) and δ13CWSOC were observed over upwelling areas and phytoplankton blooms, which was attributed to planktonic tissues being more enriched in δ13C. The δ13C analysis estimated that on average, marine sources contribute ~ 90 ± 25 % of the aerosol carbon, indicating the predominance of marine-derived carbon in the submicron WSOC. This conclusion is supported by Lagrangian trajectory analysis, which suggests that the majority of the sampling points on the ship had been exposed to marine boundary layer air for more than 80 % of the time during the previous 7 days. The combined analysis of the δ13C and monosaccharides, such as glucose and fructose, indicated that DOC concentration was the major factor controlling the concentration levels of the submicron WSOC regardless of the oceanic areas over the study region.;
