Carbonaceous particles have been confirmed as major components of ambient aerosols in urban environments and are related to climate impacts and environmental and health effects. In this study, we collected different-size particulate matter (PM) samples (PM₁, PM_2.5, and PM₁₀) at an urban site in Lanzhou, northwest China, during three discontinuous one-month periods (January, April, and July) of 2019. We measured the concentrations and potential transport pathways of carbonaceous aerosols in PM₁, PM_2.5, and PM₁₀ size fractions. The average concentrations of OC (organic carbon) and EC (elemental carbon) in PM₁, PM_2.5, and PM₁₀ were 6.98 ± 3.71 and 2.11 ± 1.34 μg/m³, 8.6 ± 5.09 and 2.55 ± 1.44 μg/m³, and 11.6 ± 5.72 and 4.01 ± 1.72 μg/m³. The OC and EC concentrations in PM₁, PM_2.5, and PM₁₀ had similar seasonal trends, with higher values in winter due to the favorable meteorology for accumulating pollutants and urban-increased emissions from heating. Precipitation played a key role in scavenge pollutants, resulting in lower OC and EC concentrations in summer. The OC/EC ratios and principal component analysis (PCA) showed that the dominant pollution sources of carbon components in the PMs in Lanzhou were biomass burning, coal combustion, and diesel and gasoline vehicle emissions; and the backward trajectory and concentration weight trajectory (CWT) analysis further suggested that the primary pollution source of EC in Lanzhou was local fossil fuel combustion.