An improved method for technetium determination in environmental samples

Results are given from the NIST component of a pilot (ldquo;winter-overapos;) study of seasonal patterns of natural and anthropogenic species in air and snow transported to Summit, Greenland. Central to this research is the quantitative apportionment of fossil and biomass particulate carbon, based on advanced (micromolar) C accelerator mass spectrometry (AMS) applied to remote snow samples containing as little as 9 micro;g C/kg. The measurements were made practicable through stringent attention to the nature and sources of the isotopic-chemical blank, resulting in a blank reduction from raquo;5 micro;g C to lt;0.5 micro;g C. An important result of this work is the first evidence of a seasonal pattern in biomass-C particles in Greenland snow. Although C AMS data serve to resolve fossil and biomass carbon quantitatively, a deeper understanding of the aerosol sources and character demands a multidisciplinary approach. This is illustrated with ldquo;multi-spectrometricapos; macro- and micro-analytical data for two cases involving substantial incursions of biomass aerosol to the Summit, Greenland snow.