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| Titel |
Cloud droplet activation of mixed organic-sulfate particles produced by the photooxidation of isoprene |
| VerfasserIn |
S. M. King, T. Rosenoern, J. E. Shilling, Q. Chen, Z. Wang, G. Biskos, K. A. McKinney, U. Pöschl, 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 ; 10, no. 8 ; Nr. 10, no. 8 (2010-04-27), S.3953-3964 |
| Datensatznummer |
250008383
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| Publikation (Nr.) |
 copernicus.org/acp-10-3953-2010.pdf |
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| Zusammenfassung |
| The cloud condensation nuclei (CCN) properties of ammonium sulfate particles mixed with
organic material condensed during the hydroxyl-radical-initiated photooxidation of isoprene
(C5H8) were investigated in the continuous-flow Harvard Environmental
Chamber. CCN activation curves were measured for organic particle mass concentrations of
0.5 to 10.0 μg m−3, NOx concentrations from under 0.4 ppbv up to
38 ppbv, particle mobility diameters from 70 to 150 nm, and thermodenuder temperatures
from 25 to 100 °C. At 25 °C, the observed CCN activation curves were
accurately described by a Köhler model having two internally mixed components, namely
ammonium sulfate and secondary organic material. The modeled physicochemical parameters of
the organic material were equivalent to an effective hygroscopicity parameter
κORG of 0.10±0.03, regardless of the C5H8:NOx
concentration ratio for the span of >200:0.4 to 50:38 (ppbv:ppbv). The volatilization
curves (i.e., plots of the residual organic volume fraction against temperature) were also
similar for the span of investigated C5H8:NOx ratios, suggesting
a broad similarity of particle chemical composition. This suggestion was supported by
limited variance at 25 °C among the particle mass spectra. For example, the signal
intensity at m/z 44 (which can result from the fragmentation of oxidized molecules
believed to affect hygroscopicity and CCN properties) varied weakly from 6 to 9% across
the range of investigated conditions. In contradistinction to the results for
25 °C, conditioning up to 100 °C in the thermodenuder significantly
reduced CCN activity. The altered CCN activity might be explained by chemical reactions
(e.g., decomposition or oligomerization) of the secondary organic material at elevated
temperatures. The study's results at 25 °C, in conjunction with the results of
other chamber and field studies for a diverse range of conditions, suggest that a value of
0.10±0.05 for κORG is representative of both anthropogenic and biogenic
secondary organic material. This finding supports the use of κORG as
a simplified yet accurate general parameter to represent the CCN activation of secondary
organic material in large-scale atmospheric and climate models. |
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