Mixed sources of water-soluble inorganic ions over the northeastern Tibetan Plateau: Anthropogenic aerosol transport versus salt lake emissions

To understand the physicochemical properties, size distribution, and pollution sources of aerosols in the northeastern Tibetan Plateau (TP), an intensive field observation campaign was conducted in the Hainan Tibetan Autonomous Prefecture during the summer of 2023. Field observations integrated optical particle counting and ion chromatography, supported by principal component analysis (PCA) and trajectory clustering. Water-soluble inorganic ions (WSII) were dominated by NH 4 + , followed by NO 3 − , SO 4 2− , and Cl − . Secondary inorganic aerosols (SIA) showed a strong positive correlation with each other, but a weaker correlation with Cl − . SIA and Cl − ions originated from different emission sources. The mass concentration size distribution exhibited a bimodal pattern dominated by an accumulation mode peak at 0.25 μm and a coarse mode peak at 5 μm with the coarse mode accounting for 89 % of the total mass concentration. Coarse particles constituted the dominant fraction of aerosols, as evidenced by the PM 2.5 /PM 10 ratio of 0.2. SIA was positively correlated with accumulation mode particles (R 2 = 0.21), whereas there was no linear relationship with coarse mode aerosols (R 2 = 0.01). PCA revealed that regional anthropogenic pollution is the dominant source. Three industrial cities in low-altitude regions were identified as potential source areas of SIA and accumulation mode aerosol, while chloride ions were derived from salt lakes on the plateau. The present study quantified the chemical composition of atmospheric aerosols in the northeastern TP and resolved their mixing sources. • Secondary inorganic aerosols originate from the long-range transport of anthropogenic emissions from low-altitude urban areas. • Salt lakes on the Tibetan Plateau produce large amounts of chloride ions. • Due to livestock emissions in local pastoral areas, ammonium dominates water-soluble inorganic ions. • The low PM 2.5 /PM 10 values demonstrate the predominance of coarse particles in the regional aerosol.