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| Titel |
Water uptake by biomass burning aerosol at sub- and supersaturated conditions: closure studies and implications for the role of organics |
| VerfasserIn |
U. Dusek, G. P. Frank, A. Maßling, K. Zeromskiene, Y. Iinuma, O. Schmid, G. Helas, T. Hennig, A. Wiedensohler, M. O. Andreae |
| 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. 18 ; Nr. 11, no. 18 (2011-09-16), S.9519-9532 |
| Datensatznummer |
250010077
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| Publikation (Nr.) |
 copernicus.org/acp-11-9519-2011.pdf |
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| Zusammenfassung |
| We investigate the CCN activity of freshly emitted biomass burning particles
and their hygroscopic growth at a relative humidity (RH) of 85%. The
particles were produced in the Mainz combustion laboratory by controlled
burning of various wood types. The water uptake at sub- and supersaturations
is parameterized by the hygroscopicity parameter, κ (c.f. Petters
and Kreidenweis, 2007). For the wood burns, κ is low,
generally around 0.06. The main emphasis of this study is a comparison of
κ derived from measurements at sub- and supersaturated conditions
(κG and κCCN), in order to see whether the water
uptake at 85% RH can predict the CCN properties of the biomass burning
particles. Differences in κGand κCCN can arise
through solution non-idealities, the presence of slightly soluble or surface
active compounds, or non-spherical particle shape. We find that κG and κCCN agree within experimental uncertainties (of
around 30%) for particle sizes of 100 and 150 nm; only for 50 nm
particles is κCCN larger than κG by a factor of 2.
The magnitude of this difference and its dependence on particle size is
consistent with the presence of surface active organic compounds. These
compounds mainly facilitate the CCN activation of small particles, which
form the most concentrated solution droplets at the point of activation. The
50 nm particles, however, are only activated at supersaturations higher than
1% and are therefore of minor importance as CCN in ambient clouds. By
comparison with the actual chemical composition of the biomass burning
particles, we estimate that the hygroscopicity of the water-soluble organic
carbon (WSOC) fraction can be represented by a κWSOC value of
approximately 0.2. The effective hygroscopicity of a typical wood burning
particle can therefore be represented by a linear mixture of an inorganic
component with κ ≅ 0.6, a WSOC component with κ ≅ 0.2, and an insoluble component with κ = 0. |
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