SummaryAir samples for polychlorinated biphenyls (PCBs), chlorinated pesticides, phthalate plasticizers, and polycyclic aromatic hydrocarbons (PAHs) were collected at three Hanford Site locations (300-Area South Gate, southeast of ZOO-East Area, and a background location near Rattlesnake Springs). Samples were collected using high-volume air samplers equipped with a glass fiber filter and polyurethane foam plug sampling train. Target compounds were extracted from the sampling trains and analyzed using capillary gas chromatography with either electron capture detection or mass selective detection.Twenty of the 28 PCB congeners analyzed were found above the detection limits, with 8 of the congeners accounting for over 80% of the average PCB concentrations. The average sum of all individual PCB congeners ranged from 500 -740 pg/m3, with little apparent difference between the sampling locations. Twenty of the 25 pesticides analyzed were found above the detection limits, with endosulfan I, endosulfan II, and methoxychlor having the highest average concentrations. With the exception of the endosulfans, all other average pesticide concentrations were below 100 pg/m3. There was little apparent difference between the air concentrations of pesticides measured at each location.Sixteen of the 18 PAHs analyzed were found above the detection limit. Phenanthrene, fluoranthene, pyrene, fluorene, chrysene, benzo(b)fluoranthene, and naphthalene were the only PAHs with average concentrations above 100 pg/m3. Overall, the 300 Area had higher average PAH concentrations compared to the ZOO-East Area and the background location at Rattlesnake Springs; however, the air concentrations at the 300-Area also are influenced by sources on the Hanford Site and from nearby communities.Two phthalate esters (PEPS) [bis(Z-ethylhexy1)phthalate and di-n-octyl phthalate], were found for a few samples; however, both compounds had high concentrations in the sample blanks, and the data should be used with caution. Despite the high blank contribution, the PEP results provided information on the upper limit air concentrations, which was useful for evaluating potential human health effects.No ambient air quality standards exist for the semivolatile organic compounds measured in this study. Therefore, the ambient air concentrations were compared to carcinogenic and non-carcinogenic risk-based concentrations.@ Ambient air concentrations below the risk-based concentrations have associated risks that are less than 1 x lo4 for cancer risk and less than 1 .O of hazard quotient for noncancer risk. All pesticide, PAH, and phthalate ester air concentrations were below the risk-based concentrations. All individual congener PCBs and average total PCB concentrations were below the risk-based concentrations. However, the maximum concentrations for total PCBs exceeded the riskbased concentrations for all three locations. A more detailed risk evaluation may be required for PCBs using individual congener air concentrations and individual congener toxicity data; however, ...