RESUMO
Total suspended particle (TSP) samples were collected during June-July 2015 in the northern South China Sea (NSCS) and August-September 2016 in the western South China Sea (WSCS). Water-soluble ions (WSIs), organic carbon (OC), elemental carbon (EC), and organic compounds were measured. The average concentrations of WSIs, OC, EC and organic compounds were 19.4 ± 10.9 µg m-3, 2.48 ± 1.54 µgC m-3, 0.31 ± 0.25 µgC m-3 and 789 ± 217 ng m-3 in the NSCS, and were 10.2 ± 4.71 µg m-3, 1.76 ± 1.82 µgC m-3, 0.43 ± 0.32 µgC m-3 and 781 ± 342 ng m-3 in the WSCS. In both cruises, sea salt ions (Na+ and Cl-) and secondary inorganic ions (SO42-, NO3-, and NH4+) were the main species of WSIs, accounting for 54.0 % and 43.6 % in the NSCS, and for 35.0 % and 54.0 % in the WSCS. The secondary products (dicarboxylic acids and aromatic acids) (NSCS: 73.3 %; WSCS: 73.9 %) and saccharides (NSCS: 19.0 %; WSCS: 18.0 %) accounted large fractions of organic compounds in aerosol particles over the SCS. These results suggest sea salt emissions and secondary formation are the main sources of the aerosols over the SCS in summer. The positive correlations between the biomass burning tracers (nss-K+ and levoglucosan) and OC as well as organic compounds indicated that biomass burning from nearby continents was also an important source of organic aerosols over the SCS. Based on back-trajectory analysis and satellite fire spots, Indochina Peninsula and China were proposed as the main continental source areas of non-sea salt WSIs and organic compounds. Our results highlight the significant contribution of continental outflow especially biomass burning and photochemical secondary oxidation to the organic compositions of aerosol particles over the SCS in summertime.
