RADON AND THORON DECAY PRODUCT AND PB-210 MEASUREMENTS AT JUNGFRAUJOCH, SWITZERLAND

During one year, the atmospheric activity concentrations of the short- lived ''radon'' (Rn-222) and ''thoron'' (Rn-220) decay products were m easured at Jungfraujoch (3450 m a.s.l.). The measurements were perform ed using a modified epiphaniometer, with a time resolution of 1 h. In addition, also the long-lived radon decay product Pb-210 was measured with a time resolution of one month. Strong seasonal variations of ail activity concentrations were found, the average summer Values being a factor of ten higher than the average winter values. During summer ti me the activity concentrations of the radon and thoron decay products showed pronounced diurnal variations. During winter these diurnal vari ations were absent, and the activity concentrations were close to free tropospheric background values. From the ratio between the activity c oncentrations of the radon decay products Pb-214 and Pb-210 a mean res idence time of aerosol particles in the atmosphere of about six days c ould be estimated. The average activity concentrations of the radon an d thoron decay products at Jungfraujoch were found to be related to th e regional soil temperatures at a near-by low altitude Swiss Midland s ite and to the static stability of the air mass between this Midland s ite and the Jungfraujoch. Furthermore, a significant correlation was f ound between the radon and thoron decay product activity concentration s and synoptic situations with higher than average activity concentrat ions for air flows from NE to SW and lower than average concentrations for air flows from W to N.