Temporal variation analysis of plutonium baseline concentration in surface air from selected sites in the continental US

The temporal variation of plutonium concentrations in surface air was assessed for the US Department of Energyʹs (DOE) monitoring sites near Richland, Washington and Chicago, Illinois using historical databases from the Batelle Pacific Northwest Laboratory (PNL) and the Argonne National Laboratory — East (ANL). The data show that 239,240Pu air concentrations post-1984 are still detectable with analytical techniques used in monitoring fallout, whereas 238Pu concentrations are not. These 239,240Pu values are suggested to represent a ‘post-fallout equilibrium’ concentration in surface air at the two DOE sites. The PNL and ANL 239,240Pu post-1984 average monthly values are mostly between 0.01 and 0.1 μBq m−3 and fall within the range observed in Europe as well as in four other US cities through the US Environmental Protection Agencyʹs Environmental Radiation Ambient Monitoring System (ERAMS) network. Temporal analysis of the post-fallout monthly data for PNL and for the three sites at ANL show that 239,240Pu concentrations fall within a predictable range of limiting values. The month-to-month fluctuations are quantified into tolerance limits at the 95% confidence level in that PNL data yielded a monthly change that was within ±0.13 μBq m−3. The limits found for the three ANL sites are ±0.14 μBq m−3 for site 12N; ±0.06 and ±0.07 μBq m−3 for sites 71 and Off-Site, respectively. Magnitudes of the monthly concentration changes are less than the observed post-fallout concentration ranges of 239,240Pu, and therefore, may be useful in flagging unexpected sources of plutonium in the environment.