Washout of particle-bound radionuclides for characterised rain and snow events on Mt. Zugspitze, Germany

Washout of radionuclides by precipitation is regarded to be an efficient deposition process depending on various parameters. Precipitation in the form of snow is suspected to be most efficient in scavenging of aerosol particles. Accidental releases of radionuclides, as seen in the recent nuclear accident of Fukushima-Daiichi in March 2011, have had serious impacts on the terrestrial environment, especially in the mountainous regions where major precipitation has fallen as snow. Supposing that wet deposition depends strongly on the type and characteristics of the precipitation event we present field experiments on the quantification of wet deposition of radionuclides by snow and rain events. The experiments took place in the free atmosphere at the Environmental Research Station Schneefernerhaus on Mt. Zugspitze, Germany (2,650 m a.s.l.). Snowfall event characterisation by meteorological and snow micro-physical parameters was carried out using a 2D video disdrometer combined with a precipitation gauge. Washout of aerosol particles in the size range from 10-2 μm to 10 μm was quantified operating an electrical low pressure cascade impactor ELPI+. Trace analysis was performed by ultra-low level gamma spectrometry (HPGe detectors) of cosmogenic 7Be, of terrigenic 210Pb (radon decay product) and of 137Cs from resuspended fallout of the Chernobyl accident in precipitation and bulk aerosol samples. Dependencies of washout efficiencies of the radionuclides on precipitation rates and snow parameters will be presented. The results shall help to improve radionuclide transport models used in modern decision support systems for emergency management (e.g. ARTM, RODOS), which do not include snow parameters so far. Proposal is made how to incorporate such parameters in future. Document available in abstract form only. (authors)