Source apportionment of water-soluble brown carbon in aerosols over the northern South China Sea: Influence from land outflow, SOA formation and marine emission

Water-soluble brown carbon (BrC) plays an important role in climate change by influencing aerosol radiative forcing. There is little information on aerosol BrC over the South China Sea (SCS). In this study, water-soluble organic carbon (WSOC) in a round-year set of aerosol samples from a remote island in the northern SCS were characterized for optical properties. In-depth information about the sources and input pathways of water-soluble BrC was obtained using molecular markers and statistic tools. The highest WSOC concentrations, light absorption coefficients at 365 nm (Abs(365)) and mass absorption efficiencies at 365 nm (MAE(365)) were observed in winter when atmospheric outflow from mainland China and the northern Indo-China Peninsula prevailed. Through the year, primary emissions from biomass burning and urban secondary organic aerosols (SOA) & waste combustion, respectively, were observed to be associated with higher MAE(365) (2.47 +/- 0.40 m(2) g(-1) and 1.97 +/- 0.22 m(2) g(-1)) and to be the main contributors to Abs(365) (22.0 +/- 3.6% and 31.6 +/- 3.6%), while biogenic SOA showed little contribution. For the first time, microorganism/plankton primary emissions, mainly from the sea, was identified to be an important contributor to water-soluble BrC (13.6 +/- 4.2% of Abs(365), MAE(365): 0.98 +/- 0.30 m(2) g(-1)), especially in spring (31% of Abs(365)). This implies that emissions from microorganism/plankton warrants careful consideration in the assessment of global aerosol light absorbance.