A general indication of the Contemporary background levels of PCDDs, PCDFs, and coplanar PCBs in the ambient air over rural and remote areas of the United States.

Long-term measurements of the atmospheric concentrations of PCDDs, PCDFs, and coplanar PCBs were taken in rural and remote areas of the United States by the National Dioxin Air Monitoring Network (NDAMN). A total of 21 quarterly sampling moments occurred from June, 1998 to December, 2002 at 34 locations geographically distributed throughout the United States. Sampling sites were located in rural and remote areas to obtain background air concentrations of dioxin-like compounds.