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| Titel |
Increased cloud activation potential of secondary organic aerosol for atmospheric mass loadings |
| VerfasserIn |
S. M. King, T. Rosenoern, J. E. Shilling, Q. Chen, S. T. Martin |
| 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 ; 9, no. 9 ; Nr. 9, no. 9 (2009-05-06), S.2959-2971 |
| Datensatznummer |
250007265
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| Publikation (Nr.) |
 copernicus.org/acp-9-2959-2009.pdf |
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| Zusammenfassung |
| The effect of organic particle mass loading from 1 to
≥100 μg m−3 on the cloud condensation nuclei (CCN)
properties of mixed organic-sulfate particles was investigated in the
Harvard Environmental Chamber. Mixed particles were produced by the
condensation of organic molecules onto ammonium sulfate particles
during the dark ozonolysis of α-pinene. A continuous-flow
mode of the chamber provided stable conditions over long time periods,
allowing for signal integration and hence increased measurement
precision at low organic mass loadings representative of atmospheric
conditions. CCN activity was measured at eight mass loadings for 80-
and 100-nm particles grown on 50-nm sulfate seeds. A two-component
(organic/sulfate) Köhler model, which included the particle
heterogeneity arising from DMA size selection and from organic volume
fraction for the selected 80- and 100-nm particles, was used to
predict CCN activity. For organic mass loadings of 2.9 μg m−3
and greater, the observed activation curves were well
predicted using a single set of physicochemical parameters for the
organic component. For mass loadings of 1.74 μg m−3 and
less, the observed CCN activity increased beyond predicted values
using the same parameters, implying changed physicochemical properties
of the organic component. A sensitivity analysis suggests that a drop in surface
tension must be invoked to explain quantitatively the CCN observations at low
SOA particle mass loadings. Other factors, such as decreased molecular weight,
increased density, or increased van't Hoff factor, can contribute to the
explanation but are quantitatively insufficient as the full explanation. |
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