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| Titel |
Technical Note: The single particle soot photometer fails to reliably detect PALAS soot nanoparticles |
| VerfasserIn |
M. Gysel, M. Laborde, A. A. Mensah, J. C. Corbin, A. Keller, J. Kim, A. Petzold, B. Sierau |
| 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.3099-3107 |
| Datensatznummer |
250003214
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| Publikation (Nr.) |
 copernicus.org/amt-5-3099-2012.pdf |
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| Zusammenfassung |
The single particle soot photometer (SP2) uses laser-induced
incandescence (LII) for the measurement of atmospheric black carbon
(BC) particles. The BC mass concentration is obtained by combining
quantitative detection of BC mass in single particles with
a counting efficiency of 100% above its lower detection limit. It
is commonly accepted that a particle must contain at least
several tenths of a femtogram BC in order to be detected by the SP2.
Here we show the result that most BC particles from a PALAS
spark discharge soot generator remain undetected by the SP2, even if
their BC mass, as independently determined with an aerosol particle
mass analyser (APM), is clearly above the typical lower detection limit of the
SP2. Comparison of counting efficiency and effective density data of
PALAS soot with flame generated soot (combustion aerosol standard
burner, CAST), fullerene soot and carbon black particles (Cabot
Regal 400R) reveals that particle morphology can affect the SP2's
lower detection limit. PALAS soot particles are fractal-like agglomerates of very
small primary particles with a low fractal dimension, resulting in
a very low effective density. Such loosely packed particles behave like "the sum
of individual primary particles" in the SP2's laser. Accordingly, most
PALAS soot particles remain undetected as the SP2's laser intensity is
insufficient to heat the primary particles to their vaporisation
temperature because of their small size
(Dpp ≈ 5–10 nm). Previous knowledge from pulsed
laser-induced incandescence indicated that particle morphology might have an
effect on the SP2's lower detection limit, however, an increase of the lower
detection limit by a factor of ∼5–10, as reported here for
PALAS soot, was not expected.
In conclusion, the SP2's lower detection limit at a certain
laser power depends primarily on the total BC mass per particle for compact
particles with sufficiently high effective density. By contrast, the
BC mass per primary particle mainly determines whether fractal-like particles
with low fractal dimension and very small primary particles are
detectable, while their total BC mass has only a minor influence. This effect shifts
the lower detection limit to much higher BC mass, or makes them completely undetectable. Consequently, care has
to be taken when using the SP2 in applications dealing with
loosely packed particles that have very small primary particles as
building blocks. |
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