Gross alpha, gross beta activities and gamma emitting radionuclides composition of airborne particulate samples in an oceanic island

The radiometric compositions of airborne particulate samples, collected weekly during a 4 years period (1 January 2000 till 31 December 2003) at a site located 310 m a.s.l. in Tenerife (Canary Islands), are analysed in this paper. To do this, measurements of gross alpha, gross beta, 7Be, 210Pb, 228Ac, 226Ra, 212Pb, 214Pb, 208Tl, 214Bi, 235U, 40K, 131I and 137Cs concentrations were carried out in 376 cellulose and polypropylene filters. The time variations of the different radionuclides concentrations have been discussed in relation with various meteorological factors and the mean values have been compared to those published in recent literature for other sites located at the same altitude but different latitudes.The weekly activities of 7Be correlated linearly with the 210Pb activities (R=0.59R=0.59). In disagreement with other published studies, the 7Be activities did not correlate (R=-0.05R=-0.05) with the temperature and maximum values were not found during summer season. The gross beta activities showed correlations with the gross alpha (R=0.72R=0.72) and 210Pb activities (R=0.52R=0.52), but not with the 7Be (R=0.16R=0.16). The anthropogenic radionuclide 131I, emitted from a nearby hospital, was detected slightly above detection limits (1.73×10−6 Bq m−3) in 88 of the 210 weeks of measurement considered in this work. 137Cs was detected in 31 of those weeks. The 4-year average calculated for 7Be and 210Pb were 3 and 0.3 mBq m−3, respectively. These values are lower than those expected for a site at comparable latitude and altitude. In general, the radionuclides which appeared most frequently in the airborne particulate filters (7Be, 210Pb, 212Pb and 40K), did not correlate significantly with any of the meteorological parameters considered: rainfall, temperature, pressure, relative humidity, visibility, wind speed and direction. Therefore, no predictive model could be established with the available data as it has been done for continental sites. The long-range transport of aerosols from the Saharan desert showed to be an important source of 137Cs and 40K in the particulate filters after low-level atmospheric dust intrusions that reached the island.