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| Titel |
Toward a standardised thermal-optical protocol for measuring atmospheric organic and elemental carbon: the EUSAAR protocol |
| VerfasserIn |
F. Cavalli, M. Viana, K. E. Yttri, J. Genberg, J.-P. Putaud |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1867-1381
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 3, no. 1 ; Nr. 3, no. 1 (2010-01-26), S.79-89 |
| Datensatznummer |
250000815
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| Publikation (Nr.) |
 copernicus.org/amt-3-79-2010.pdf |
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| Zusammenfassung |
| Thermal-optical analysis is a conventional method for determining the
carbonaceous aerosol fraction and for classifying it into organic carbon,
OC, and elemental carbon, EC. Unfortunately, the different thermal evolution
protocols in use can result in a wide elemental carbon-to-total carbon
variation by up to a factor of five. In Europe, there is currently no
standard procedure for determining the carbonaceous aerosol fraction which
implies that data from different laboratories at various sites are of
unknown accuracy and cannot be considered comparable. In the framework of
the EU-project EUSAAR (European Supersites for Atmospheric Aerosol
Research), a comprehensive study has been carried out to identify the causes
of differences in the EC measured using different thermal evolution
protocols; thereby the major positive and negative biases affecting
thermal-optical analysis have been isolated and minimised to define an
optimised protocol suitable for European aerosols. Our approach to improve
the accuracy of the discrimination between OC and EC was essentially based
on four goals. Firstly, charring corrections rely on faulty assumptions –
e.g. pyrolytic carbon is considered to evolve completely before native EC
throughout the analysis –, thus we have reduced pyrolysis to a minimum by
favoring volatilisation of OC. Secondly, we have minimised the potential
negative bias in EC determination due to early evolution of light absorbing
carbon species at higher temperatures in the He-mode, including both native
EC and combinations of native EC and pyrolytic carbon potentially with
different specific attenuation cross section values. Thirdly, we have
minimised the potential positive bias in EC determination resulting from the
incomplete evolution of OC during the He-mode which then evolves during the
He/O2-mode, potentially after the split point. Finally, we have
minimised the uncertainty due to the position of the OC/EC split point on
the FID response profile by introducing multiple desorption steps in the
He/O2-mode. Based on different types of carbonaceous PM encountered
across Europe, we have defined an optimised thermal evolution protocol, the
EUSAAR_2 protocol, as follows: step 1 in He, 200 °C for 120 s; step 2
in He 300 °C for 150 s; step 3 in He 450 °C for 180 s; step 4 in He
650 °C for 180 s. For steps 1–4 in He/O2, the conditions are
500 °C for 120 s, 550 °C for 120 s, 700 ° C for 70 s,
and 850 °C for 80 s, respectively. |
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