Archived extracts from two air sampling campaigns were used to investigate PCNs in the U.K. atmosphere. In the first study, daily air samples were collected at a semi-rural location (Hazelrigg) in northwest England in 1994. Air parcel back-trajectories were used to distinguish air masses that stemmed from distinct sectors, and 18 samples representing four regions (Arctic/Scandinavia; Atlantic; mainland Europe; U.K.) were selected for PCN analysis. The mean for all samples was ∑PCN = 59 pg m-3 and ∑PCN/∑PCB = 0.31 with a profile that was dominated by the 3-Cl and 4-Cl PCN homologue groups. Atmospheric concentrations of PCN and the ratio ∑PCN/∑PCB were lowest for samples that had trajectories that stemmed from the Arctic/Scandinavia sector20 pg m-3 and 0.24, respectively. Highest values were observed for air that lingered over the U.K. before arriving at the sampling site108 pg m-3 and 0.41, respectively. These results are consistent with elevated PCN burdens in the eastern Arctic Ocean for air samples that stemmed from the U.K. region and suggest that the U.K. is a significant emission source of PCNs. On the basis of this study, we also conclude that a ∑PCN/∑PCB ratio of 0.2−0.25 is characteristic of background air resulting from diffuse emission sources and that a ratio much greater than 0.25 indicates an increasing contribution from “nondiffuse” or “point sources” of PCNs. In the second study, extracts were obtained for 1998−1999 from four stations operated under the TOMPS monitoring programManchester (urban), Hazelrigg (semi-rural), Stoke Ferry (rural), and High Muffles (rural). PCN air burdens were highest at Manchester (138−160 pg m-3) and decreased to 22−35 pg m-3 at the rural sites.