Evaluation of an early warning system for airborne radionuclides

An early warning system for detection of increased levels of radioactivity in outdoor air was operative between 2004 and 2011 at the Swedish air sampling stations. The system consisted of a low resolution detector (NaI), positioned directly behind the filter and measurement of the accumulated radioactivity were performed continuously. An evaluation of the data collected during the period is presented with emphasis on natural occurring radionuclides and their influence on the detectability of anthropogenic radionuclides.