Water-soluble organic nitrogen in PM2.5 around the Danjiangkou Reservoir: Concentration, sources, and transport pathways

Abstract

Water-soluble organic nitrogen (WSON) affects the formation, hygroscopicity, acidity of organic aerosols, and nitrogen biogeochemical cycles. However, qualitative and quantitative characterizations of WSON remain limited due to its chemical complexity. In the study, 1-year field samples of particulate matter 2.5 (PM_2.5) were collected from June 2022 to May 2023 to analyze the WSON concentration in PM_2.5, and correlation analysis, positive matrix factor (PMF), and potential source contribution function (PSCF) models were employed to elucidate WSON source apportionment and transport pathways. The results revealed that the mean WSON concentrations reached 1.98 ± 2.64 µg/m³ with a mean WSON to water-soluble total nitrogen (WSTN) ratio of 21 %. Further, WSON concentration exhibited a seasonal variation trend, with higher values in winter and lower in summer. Five sources were identified as contributors to WSON in PM_2.5 within the reservoir area through a comprehensive analysis including correlation analysis, PSCF and concentration weighted trajectory (CWT), and PMF analyses. These sources were agricultural, dust, combustion, traffic, and industrial sources, of which agricultural source emerged as the primary contributor (76.69 %). The atmosphere in the reservoir area were primarily influenced by the transport of northeastern air masses, local agricultural activities, industrial cities along the trajectory, and coastal regions, exerting significant influences on the concentration of WSON in the reservoir area. The findings of this study addressed the research gap concerning organic nitrogen in PM_2.5 within the reservoir area, thereby offering a theoretical foundation and data support in controlling nitrogen pollution in the Danjiangkou Reservoir area.