Remote sources of airborne lanthanoids and actinoids collected in the Azores’ lower free troposphere, studied with k0-INAA

The location of Azores turns it into an ideal platform for tracking the long-range transport of air masses from surrounding continents over the North Atlantic Ocean. Aerosol samples (PM10) have been collected using an aethalometer located at PICO-NARE observatory, in Pico island, from 15 July 2001 to 18 April 2004. The instrument is at an altitude of 2225 m above mean sea level (AMSL), and sampled for 24 h in most cases, and for a few periods continuously. The data herein refer to daily collections of PM10 in the period July 2001–July 2002. Samples were assessed through instrumental neutron activation analysis, k0-variant (k0-INAA). The lanthanoids and actinoids with concentrations above detection limits and above blank backgrounds were La, Sm, Lu, and Th, U, respectively. Back-trajectory results by the HYSPLIT model have shown that the highest values of La are of African origin, likely related to Saharan-dust episodes, while U comes mainly from northern Europe and North-Central America, down to the Caribbean. Every element presents the same enrichment-factor pattern concerning its annual, summer and winter averages. As for lanthanoids, La and Sm are not enriched relatively to soil while Lu is (actinoids are enriched as well), which indicates preferential enrichment of heavy rare earths compared to the light ones.