Program

Dissolved organic carbon (DOC) in oceanic aerosol is an important external source of DOC to the ocean. The chemical composition of water soluble organic carbon (WSOC) in oceanic atmosphere therefore may have the potential to affect the microbial food web and the oceanic refractory DOC pool. However, up to date, very limited information is available regarding the sources and composition of oceanic WSOC. The recent implication of ultrahigh mass spectrometry Fourier Transform ion Cyclotron Resonance Mass Spectrometry (FT-ICR-MS) had largely improved our knowledge on the molecular compositions. Here we applied FT-ICR-MS to characterize the molecular composition of WSOC in the aerosols collected from China coastal seas to Northwestern Pacific outflow of the North China during dust outbreak and biomass burning season. Samples were separated into three groups according to their sampling locations, backward trajectories and satellite images, namely, the China coastal seas, dust and open ocean aerosols. Our objective was to understand the molecular composition of WSOC in the aerosols. WSOC concentrations ranged from 6.8 to 835.0 nmol C m-3, and decreased from the China coastal seas to the open ocean aerosols, except for the dust aerosols. FT-ICR-MS results showed that approximately 2600-6800 molecular formulas can be assigned to each sample. A large number of molecular formulas in all the samples resembled polyphenols. The Bray-Curtis distance based on the molecular composition varied from 0.12-0.74, suggesting distinct molecular compositions among samples. Principal coordinates analysis (PCoA) based on the molecular composition can well separate those aerosol samples, and the results were highly consistent with the origins of aerosols. Compare to dust and China coastal seas aerosols, open ocean aerosols contained higher fraction of saturated compounds, likely from aquatic organism derived from the ocean spray; while China coastal seas aerosols presented larger amount of sulfur containing compounds compared to other aerosols. Our results suggested molecular composition of WSOC in oceanic aerosols were highly related to their origin, the impact of atmospheric deposition on the ocean DOC pool requires further study.