[Characteristics and Sources of Water-soluble Organic Carbon/Nitrogen in PM_2.5 During Spring in Changzhou]

To understand the characteristics and sources of water-soluble organic carbon (WSOC) and organic nitrogen (WSON) in atmospheric aerosols during spring in Changzhou, 84 fine particle (PM_2.5) samples were collected from March 1 to May 30, 2017, in Changzhou. The water-soluble components, including water-soluble organic carbon, water-soluble total nitrogen (WSTN), water-soluble ions, and carbonaceous components (OC and EC), were analyzed. The levels of WSOC and WSON and their source characteristics were discussed. The results show that the average concentrations of PM_2.5, WSOC, and WSON are 101.97, 7.63, and 1.50 μg·m^-3, respectively, during the sampling period. The WSON accounts for 12.9% of the WSTN and the water-soluble inorganic nitrogen mainly exists in two forms, that is, NH₄⁺ and NO₃^-, accounting for 86.15% of the WSTN. The WSOC is weakly correlated with WSON (r=0.58), indicating that WSOC and WSON do not have the same sources. The WSOC is related to SOC, K⁺, and secondary ions (SO₄^2-, NH₄⁺, and NO₃^-), indicating that it is mainly derived from biomass burning and secondary conversion; WSON is strongly correlated to secondary ions, indicating that it is mainly derived from secondary conversion. The wind speed is the main factor affecting the WSOC and WSON concentration levels. Furthermore, the WSON is positively correlated with the air pressure and negatively correlated with the temperature. The results of the principal component analysis show that PM_2.5 mainly originates from four sources:secondary formation, dust, coal combustion, biomass burning, and the ocean. The backward trajectory analysis indicates that the total concentrations of PM_2.5, WSOC, and WSON in air masses from long-distance transformation are higher than that from short-distance transmission, whereas there is no significant difference in the WSON/WSTN ratio from different transmission paths.