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| Titel |
Cloud condensation nuclei in polluted air and biomass burning smoke near the mega-city Guangzhou, China – Part 2: Size-resolved aerosol chemical composition, diurnal cycles, and externally mixed weakly CCN-active soot particles |
| VerfasserIn |
D. Rose, S. S. Gunthe, H. Su, R. M. Garland, H. Yang, M. Berghof, Y. F. Cheng, B. Wehner, P. Achtert, A. Nowak, A. Wiedensohler, N. Takegawa, Y. Kondo, M. Hu, Y. Zhang, M. O. Andreae, U. Pöschl |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 11, no. 6 ; Nr. 11, no. 6 (2011-03-25), S.2817-2836 |
| Datensatznummer |
250009523
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| Publikation (Nr.) |
 copernicus.org/acp-11-2817-2011.pdf |
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| Zusammenfassung |
Size-resolved chemical composition, mixing state, and cloud condensation nucleus (CCN) activity of aerosol
particles in polluted mega-city air and biomass burning smoke were measured
during the PRIDE-PRD2006 campaign near Guangzhou, China, using an aerosol
mass spectrometer (AMS), a volatility tandem differential mobility analyzer
(VTDMA), and a continuous-flow CCN counter (DMT-CCNC).
The size-dependence and temporal variations of the effective average
hygroscopicity parameter for CCN-active particles (κa) could be
parameterized as a function of organic and inorganic mass fractions (forg, finorg)
determined by the AMS: κa,p=κorg·forg +
κinorg·finorg. The characteristic κ values of
organic and inorganic components were similar to those observed in other
continental regions of the world: κorg≈0.1 and
κinorg≈0.6. The campaign average κa
values increased with particle size from ~0.25 at ~50 nm to
~0.4 at ~200 nm, while forg decreased with particle size.
At ~50 nm, forg was on average 60% and increased to almost
100% during a biomass burning event.
The VTDMA results and complementary aerosol optical data suggest that the
large fractions of CCN-inactive particles observed at low supersaturations
(up to 60% at S≤0.27%) were externally mixed weakly CCN-active soot particles with low
volatility (diameter reduction <5% at 300 °C) and effective
hygroscopicity parameters around κLV≈0.01. A proxy for
the effective average hygroscopicity of the total ensemble of CCN-active particles
including weakly CCN-active particles (κt) could be parameterized as a function
of κa,p and the number fraction of low volatility particles
determined by VTDMA (φLV):
κt,p=κa,p−φLV·(κa,p−κLV).
Based on κ values derived from AMS and VTDMA data, the observed CCN
number concentrations (NCCN,S≈102–104 cm−3 at
S = 0.068–0.47%) could be efficiently predicted from the measured particle
number size distribution. The mean relative deviations between observed and
predicted CCN concentrations were ~10% when using κt,p,
and they increased to ~20% when using only κa,p. The mean
relative deviations were not higher (~20%) when using an approximate
continental average value of κ≈0.3, although the constant
κ value cannot account for the observed temporal variations in
particle composition and mixing state (diurnal cycles and biomass burning
events).
Overall, the results confirm that on a global and climate modeling scale
an average value of κ≈0.3 can be used
for approximate predictions of CCN number concentrations in continental
boundary layer air when aerosol size distribution data are available without
information about chemical composition. Bulk or size-resolved data on aerosol
chemical composition enable improved CCN predictions resolving regional and temporal
variations, but the composition data need to be highly accurate and
complemented by information about particle mixing state to achieve high
precision (relative deviations <20%). |
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