Abstract: The study of atmospheric particulate matter pollution characteristics and sources over Qinghai–Xizang Plateau is of considerable scientific importance for ecological environmental protection and climate change impact assessment in this region. Using observational data from the Second Qinghai–Xizang Plateau Scientific Expedition and Research Program collected in Ali during July–August 2019, surface observations from the Shiquanhe National Climate Station, and meteorological fields from the Global Data Assimilation System (GDAS1), this study investigated the characteristics, source regions, and contributions of atmospheric particulate matter in the western Qinghai–Xizang Plateau during summer. The source-resolved PMF (positive matrix factorization) model, backward trajectory cluster analysis, and CWT (concentration-weighted trajectory) analysis were employed. Results show that TSP (total suspended particulates) in the Ali region mainly consist of mineral dust (48.7%), organic matter (37.6%), nondust water-soluble inorganic ions (12.7%), and elemental carbon (0.9%). The concentrations of metal elements in sand and dust were positively correlated with wind speed. Elevated potassium concentrations and high organic carbon to elemental carbon ratios (OC/EC) suggest that biomass burning exerts a stronger influence than fossil fuel combustion in the western plateau. PMF results identified four main pollution sources: mineral dust (38%), secondary formation (28%), biomass burning (27%), and fossil fuel combustion (7%). Overall, natural dust emissions and anthropogenic organic aerosols from biomass burning are the dominant contributors to particulate matter in the western Qinghai–Xizang Plateau. Backward trajectory distance clustering and CWT analysis indicate that external pollutants are mainly transported over short distances from South Asia, with particularly significant influence from northwestern India. In particular, anthropogenic aerosols—including organic carbon, elemental carbon, sulfate, and biomass burning emissions—from India substantially affect particulate matter concentrations in the region. In contrast, local dust is primarily generated by strong surface winds, with additional contributions from northwestern India and minor influence from the Taklamakan Desert.