Atmospheric deposition can be an important pathway for the delivery of toxic polychlorinated biphenyls (PCBs) to ecosystems, especially in remote areas. Determining the sources of atmospheric PCBs can be difficult, because PCBs may travel long distances to reach the monitoring location, allowing for a variety of weathering processes that may alter PCB fingerprints. Previous efforts to determine the sources of atmospheric PCBs have been hampered by the electron capture detection methods used to measure PCBs. In this work, EPA method 1668, which is capable of measuring all 209 congeners, was used to measure PCBs in bulk atmospheric deposition at seven locations in the Green-Duwamish River watershed in and near Seattle, WA. Analysis of this data set via Positive Matrix Factorization allowed the identification of six factors that represent PCB sources. Four factors, representing approximately 88% of all PCB mass, are strikingly similar to unweathered Aroclors, suggesting minimal weathering during transport and/or local PCB sources at some sites. A fifth factor contained virtually all of the PCB 11 mass and represents PCBs from pigments. It explained approximately 39% of the Toxic Equivalency Quotient in the atmospheric deposition samples. The remaining factor contained non-Aroclor PCBs and may be related to silicone.