Atmospheric Chemistry and Physics Discussions
www.atmos-chem-phys-discuss.net
1680-7367
1680-7375
5
3
2005
10.5194/acpd-5-3341-2005
http://www.atmos-chem-phys-discuss.net/5/3341/2005/
http://www.atmos-chem-phys-discuss.net/5/3341/2005/acpd-5-3341-2005.html
http://www.atmos-chem-phys-discuss.net/5/3341/2005/acpd-5-3341-2005.pdf
3341
3366
2005-05-26
On the isolation of elemental carbon for micro-molar <sup>14</sup>C accelerator mass spectrometry; evaluation of alternative isolation procedures, and accuracy assurance using a hybrid isotopic particulate carbon reference material
L. A. Currie
J. D. Kessler
National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
now at: Department of Earth System Science, University of California Irvine, Irvine, CA 92697, USA
The primary objective of the research reported here has
been the development of an hybrid reference material (RM) to serve as a test
of accuracy for elemental carbon (EC) isotopic (<sup>14</sup>C) speciation
measurements. Such measurements are critically important for the
quantitative apportionment of fossil and biomass sources of ''soot'' (EC),
the tracer of fire that has profound effects on health, atmospheric
visibility, and climate. Previous studies of <sup>14</sup>C-EC measurement
quality, carried out with NIST SRM 1649a (Urban Dust), showed a range of results, but
since the ''truth'' was not known for this natural matrix RM, one had to
rely on isotopic-chemical consistency evidence (<sup>14</sup>C in PAH, EC) of
measurement validity (Currie et al., 2002). Components of the new Hybrid RM
(DiesApple), however, have known <sup>14</sup>C and EC composition, and they are nearly
orthogonal (isotopically and chemically). NIST SRM 2975 (Forklift Diesel Soot)
has little or no <sup>14</sup>C, and its major compositional component is EC.
SRM 1515 (Apple Leaves) has the <sup>14</sup>C content of biomass-C, and it has
little or no EC. Thus, the hybrid RM can serve as an absolute isotopic test
for the absence of EC-mimicking pyrolysis-C from SRM 1515 in the EC isolate
of the hybrid RM, together with testing for conservation of its dominant
soot fraction through the isolation procedure.