The Sources, Molecular Compositions, and Light Absorption Properties of Water‐Soluble Organic Carbon in Marine Aerosols From South China Sea to the Eastern Indian Ocean

Abstract

AbstractWater‐soluble organic carbon (WSOC) is a substantial component of carbonaceous aerosols in South/East Asia. However, the poorly constrained sources, molecular compositions, and light absorption properties of WSOC over South/East Asian marine regions lead to large uncertainty in climate effects. Herein, we collected marine aerosol samples from South China Sea to the eastern Indian Ocean to investigate the sources, molecular compositions, and light absorption properties of WSOC. The δ13C of Marine‐influenced WSOC (−20.6 ± 1.4‰) was higher than those in Continent‐influenced (South Asia‐influenced: −24.4 ± 1.1‰ and Southeast Asia‐influenced: −22.7 ± 1.0‰, p < 0.01) regions. Additionally, combining with 5‐day back trajectories and the relationships of δ13C‐WSOC with chemical tracers (Cl−/Na+ and nonsea salt K+/K+), we found that the Marine‐influenced WSOC was mostly related to oceanic emissions, which was more enriched in saturated primary marine biological compounds with lower oxidation level. In contrast, the Continent‐influenced WSOC was significantly affected by C3 biomass burning and secondary organic aerosols formation, and it has a higher fraction of aromatic and highly oxidized compounds. Moreover, the high aromatic level of Continental‐influenced WSOC may result in high mass absorption efficiency at 365 nm (MAE365) but low absorption Ångström exponent (AAE) values. Taken together with previous WSOC light absorption properties studies, we found that the MAE365 of WSOC in urban, rural and background, and marine regions correlated well with AAE. However, the response and correlation coefficients of MAE365 to AAE were highest in urban regions, followed by rural and background and marine regions, which is likely associated with different aromatic compound contents. Therefore, in the future, more attention should be paid to the sources and atmospheric processes of condensed aromatic compounds.