Trends in Ambient Air Alpha Activity Concentrations Due to Wildfires

摘要

A network of high-volume,size-partitioning particulate matter air samplers at the Rocky Flats Environmental Technology Site(RFETS),a former Department of Energy weapons production facility,continuously samples near Denver,Colorado.The sampling effort,known as the Radioactive Ambient Air Monitoring Program(RAAMP),measures radioactivity in ambient air originating from both RFETS sources and naturally-occurring background sources.During the summer of 2002,regional wildfires increased airborne particulate matter concentrations around Denver.Studies from Africa and New Mexico suggest that wildfires may resuspend naturally occurring radionuclides from soils and vegetation;increased alpha activity in RAAMP samples correlated well with wildfire events,consistent with these observations.RAAMP data were compared qualitatively to RFETS activities,the locations and size of corresponding regional wildfires,and local and regional meteorological data.Additionally,data were compared quantitatively to historical RAAMP alpha concentration data.Isotopic analyses of selected RAAMP samples quantified the contribution of RFETS-derived alpha emitters to samples,resolving the contribution of non-RFETS radionuclides to RAAMP alpha concentrations.Isotopic analyses of the most impacted samples verified that Site contaminants were insufficiently elevated to contribute the high alpha activity;these and other indicators point to long-lived radon daughters as the likely contributors to elevated alpha activity.