Variation in airborne 134 Cs, 137 Cs, particulate 131 I and 7 Be maximum activities at high-altitude European locations after the arrival of Fukushima-labeled air masses

The Fukushima-labeled air mass arrival, and later the cesium-134 ( Cs), cesium-137 ( Cs) and particulate iodine-131 (hereafter noted I ) maximum levels were registered in Europe at different dates depending on the location. Most of those data were obtained at low-altitude sampling areas. Here, we compare the airborne levels registered at different high-altitude European locations (from 850 m to about 3500 m). The integrated Cs activity concentration was not uniform with regard to the altitude even after a long travel time/distance from Japan. Moreover, the relation of integrated Cs vs. altitude showed a linear decrease up to an altitude of about 3000 m. A similar trend was noticed for I (particulate fraction) while it increased above 3000 m. Comparison with Be activity concentration showed that, as far as the high altitude location is concerned, the Cs and Cs maximum concentrations corresponded to the Be maximum, suggesting downdraft movements from high tropospheric or stratospheric layers to be responsible for Cs increase and peak values. This was also confirmed by high potential vorticity and low relative humidity registered during the peak values.