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| Titel |
Single Particle Soot Photometer intercomparison at the AIDA chamber |
| VerfasserIn |
M. Laborde, M. Schnaiter, C. Linke, H. Saathoff, K.-H. Naumann, O. Möhler, S. Berlenz, U. Wagner, J. W. Taylor, D. Liu, M. Flynn, J. D. Allan, H. Coe, K. Heimerl, F. Dahlkötter, B. Weinzierl, A. G. Wollny, M. Zanatta, J. Cozic, P. Laj, R. Hitzenberger, J. P. Schwarz, M. Gysel |
| 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 ; 5, no. 12 ; Nr. 5, no. 12 (2012-12-20), S.3077-3097 |
| Datensatznummer |
250003213
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| Publikation (Nr.) |
 copernicus.org/amt-5-3077-2012.pdf |
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| Zusammenfassung |
Soot particles, consisting of black carbon (BC), organic carbon (OC),
inorganic salts, and trace elements, are emitted into the atmosphere during
incomplete combustion. Accurate measurements of atmospheric BC are important
as BC particles cause adverse health effects and impact the climate.
Unfortunately, the accurate measurement of the properties and mass
concentrations of BC particles remains difficult. The Single Particle Soot
Photometer (SP2) can contribute to improving this situation by measuring the
mass of refractory BC in individual particles as well as its mixing state.
Here, the results of the first detailed SP2 intercomparison, involving 6 SP2s
from 6 different research groups, are presented, including the most evolved
data products that can presently be calculated from SP2 measurements.
It was shown that a detection efficiency of almost 100% down to 1 fg
BC per particle can readily be achieved, and that this limit can be pushed
down to ∼0.2 fg BC with optimal SP2 setup. Number and mass size
distributions of BC cores agreed within ±5% and ±10%, respectively,
in between the SP2s, with larger deviations in the range below 1 fg
BC.
The accuracy of the SP2's mass concentration measurement
depends on the calibration material chosen. The SP2 has previously been shown
to be equally sensitive to fullerene soot and ambient BC from sources where
fossil fuel was dominant and less sensitive to fullerene soot than to
Aquadag. Fullerene soot was therefore chosen as the standard calibration
material by the SP2 user community; however, many data sets rely solely on
Aquadag calibration measurements. The difference in SP2 sensitivity was found
to be almost equal (fullerene soot to Aquadag response ratio of ∼0.75 at
8.9 fg BC) for all SP2s. This allows the calculation of a fullerene
soot equivalent calibration curve from a measured Aquadag calibration, when
no fullerene soot calibration is available. It could be shown that this
approach works well for all SP2s over the mass range of 1–10 fg.
This range is suitable for typical BC mass size distributions in the ambient
air far from sources.
The number size distribution of purely scattering particles optically
measured by the 6 SP2s also agreed within 15%. Measurements of the thickness
of non-refractory coatings (i.e. product from α-pinene ozonolysis) on
the BC particles, relying on BC mass optical size and on an additional
particle position measurement, also compared well (within ±17%). The
estimated coating thickness values were consistent with thermo-optical
analysis of OC and elemental carbon (EC) content, though absolutely accurate values cannot be
expected given all the assumptions that have to be made regarding refractive
index, particle morphology, etc.
This study showed that the SP2 provides accurate and reproducible data, but
also that high data quality is only achieved if the SP2 is carefully tuned
and calibrated. It has to be noted that the agreement observed here does not
account for additional variability in output data that could result from the
differences in the potentially subjective assumptions made by different SP2
users in the data processing. |
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