Relationship between variations of 7Be, 210Pb and 212Pb concentrations and sub-regional atmospheric transport: Simultaneous observation at distant locations

In order to investigate the applicability of Pb-212 as a tracer for atmospheric transportin the sub-regional scale (few hundred kilometers in horizontal direction and up to similar to 1 km by height), we measured the air concentrations of the short-lived radionuclide Pb-212 along with the long-lived Be-7 and Pb-212 near the ground surface. For this purpose, simultaneous observations were continued for several days at three locations: a reference point representative for standard land surface atmosphere conditions, a second location at an altitude 650 m near the reference point, and on a solitary island similar to 180 km from the reference point. Measurements of radioactivity in aerosol particle samples collected at intervals of 2-3 h with a high-volume air sampler were performed by extremely low background gamma-ray spectrometry with the use of Ge detectors located at the Ogoya Underground Laboratory. Concentration of Be-7 or Pb-212 and their variation patterns was found to be similar among the three points during the whole observation period except for moment of the passage of a cold front. The results indicate that distributions of concentrations of the long-lived nuclides were uniform in this range. On the other hand, concentration levels and the variation patterns of the short-lived Pb-212 differed greatly from one location to another, reflecting differences in geographical location and altitude of the observation points. Additionally, there were certain indications that observed concentration of Pb-212 contained two components: an autogenous component from sources nearby and a heterogenous one from fat-away sources carried by atmospheric horizontal transport. Results of this study provide experimental proof that Pb-212 can be used as a tracer of sub-regional atmospheric transport. (C) 2009 Elsevier Ltd. All rights reserved.