The study of atmospheric particulate matter pollution characteristics and their sources on the Tibetan Plateau is of great significance for the ecological environmental protection of the Tibetan Plateau and for the ability to cope with the adverse effects of climate change. In this paper, we analyze the characteristics of atmospheric particulate matter using observational data from the second Qinghai-Tibetan Science Expedition in Ali in July-August 2019, as well as observational data from the Ali Shiquanhe National Climate Station and GDAS1 data. The distribution of source areas and the degree of contribution of pollution to the western Tibetan Plateau in summer are analyzed using the source-resolved positive-definite matrix factor decomposition model, the backward trajectory-distance clustering, and the concentration-weighted trajectory analysis, among other techniques. The main conclusions are as follows: The TSP in the Ali region of the western Tibetan Plateau in summer is composed of sand and dust, organic matter, non-dust water-soluble inorganic ions, and singlet carbon. The pollution can be attributed to four main sources, namely sand and dust, secondary generation, biomass burning and fossil fuel combustion. The impact of biomass burning in the western part of the plateau is significantly greater than that of fossil fuel burning. The naturally emitted sand and dust, along with the anthropogenic organic aerosols from biomass burning, constitute the primary components of particulate matter in the western Tibetan Plateau. Notably, biomass burning in India has a considerable influence on the particulate matter concentrations in the western Tibetan Plateau.