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| Titel |
Influence of particle size and chemistry on the cloud nucleating properties of aerosols |
| VerfasserIn |
P. K. Quinn, T. S. Bates, D. J. Coffman, D. S. Covert |
| 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 ; 8, no. 4 ; Nr. 8, no. 4 (2008-02-26), S.1029-1042 |
| Datensatznummer |
250005681
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| Publikation (Nr.) |
 copernicus.org/acp-8-1029-2008.pdf |
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| Zusammenfassung |
| The ability of an aerosol particle to act as a cloud condensation nuclei
(CCN) is a function of the size of the particle, its composition and mixing
state, and the supersaturation of the cloud. In-situ data from field studies
provide a means to assess the relative importance of these parameters.
During the 2006 Texas Air Quality – Gulf of Mexico Atmospheric Composition
and Climate Study (TexAQS-GoMACCS), the NOAA RV Ronald H. Brown encountered a wide variety
of aerosol types ranging from marine near the Florida panhandle to urban and
industrial in the Houston-Galveston area. These varied sources provided an
opportunity to investigate the role of aerosol sources and chemistry in the
potential activation of particles to form cloud droplets. Measurements were
made of CCN concentrations, aerosol chemical composition in the size range
relevant for particle activation in warm clouds, and aerosol size
distributions. Variability in aerosol composition was parameterized by the
mass fraction of Hydrocarbon-like Organic Aerosol (HOA) for particle
diameters less than 200 nm (vacuum aerodynamic). The HOA mass fraction in
this size range was lowest for marine aerosol and highest for aerosol
sampled close to anthropogenic sources. Combining all data from the
experiment reveals that composition (defined by HOA mass fraction) explains
40% of the variance in the critical diameter for particle activation at
the instrumental supersaturation (S) of 0.44%. Correlations between HOA
mass fraction and aerosol mean diameter show that these two parameters are
essentially independent of one another for this data set. We conclude that,
based on the variability of the HOA mass fraction observed during
TexAQS-GoMACCS, variability in particle composition played a significant
role in determining the fraction of particles that could activate to form
cloud droplets. Using a simple model based on Köhler theory and the
assumption that HOA is insoluble, we estimate the degree to which calculated
CCN concentrations are under- or overestimated if the variability in the HOA
mass fraction that was observed during TexAQS-GoMACCS is neglected. The
percent under- or overestimation in the CCN concentration is related to the
source of the aerosol. Relative to the mean HOA mass fraction of 0.4±0.2
(average ±1σ standard deviation) for the entire
experiment, CCN concentrations are underestimated by up to 50% (at
0.22% S) for aerosol sampled far from anthropogenic source regions as it
had a lower HOA mass fraction and overestimated by up to 50% for
organic-rich aerosol sampled near the source as it had a higher HOA mass
fraction. |
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