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| Titel |
Analysis of CCN activity of Arctic aerosol and Canadian biomass burning during summer 2008 |
| VerfasserIn |
T. L. Lathem, A. J. Beyersdorf, K. L. Thornhill, E. L. Winstead, M. J. Cubison, A. Hecobian, J. L. Jimenez, R. J. Weber, B. E. Anderson, A. Nenes |
| 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 ; 13, no. 5 ; Nr. 13, no. 5 (2013-03-08), S.2735-2756 |
| Datensatznummer |
250018481
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| Publikation (Nr.) |
 copernicus.org/acp-13-2735-2013.pdf |
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| Zusammenfassung |
| The NASA DC-8 aircraft characterized the aerosol properties, chemical
composition, and cloud condensation nuclei (CCN) concentrations of the
summertime Arctic during the 2008 NASA Arctic Research of the Composition of
the Troposphere from Aircraft and Satellites (ARCTAS) campaign. Air masses
characteristic of fresh and aged biomass burning, boreal forest, Arctic
background, and anthropogenic industrial pollution were sampled. Observations
were spatially extensive (50–85° N and 40–130° W) and
exhibit significant variability in aerosol and CCN concentrations. The
chemical composition was dominated by highly oxidized organics (66–94% by
volume), with a water-soluble mass fraction of more than 50%. The aerosol
hygroscopicity parameter, κ, ranged between κ = 0.08–0.32
for all air mass types. Industrial pollution had the lowest κ of
0.08 ± 0.01, while the Arctic background had the highest and most
variable κ of 0.32 ± 0.21, resulting from a lower and more
variable organic fraction. Both fresh and aged (long-range transported)
biomass burning air masses exhibited remarkably similar κ
(0.18 ± 0.13), consistent with observed rapid chemical and physical
aging of smoke emissions in the atmosphere, even in the vicinity of fresh
fires. The organic hygroscopicity (κorg) was parameterized
by the volume fraction of water-soluble organic matter
(εWSOM), with a κ = 0.12, such that
κorg = 0.12εWSOM. Assuming bulk
(size-independent) composition and including the κorg
parameterization enabled CCN predictions to within 30% accuracy for nearly
all environments sampled. The only exception was for industrial pollution
from Canadian oil sands exploration, where an external mixture and
size-dependent composition was required. Aerosol mixing state assumptions
(internal vs. external) in all other environments did not significantly
affect CCN predictions; however, the external mixing assumption provided the
best results, even though the available observations could not determine the
true degree of external mixing and therefore may not always be representative
of the environments sampled. No correlation was observed between
κorg and O : C. A novel correction of the CCN instrument
supersaturation for water vapor depletion, resulting from high concentrations
of CCN, was also employed. This correction was especially important for fresh
biomass burning plumes where concentrations exceeded
1.5×104 cm−3 and introduced supersaturation depletions of
≥25%. Not accounting for supersaturation depletion in these high
concentration environments would therefore bias CCN closure up to 25% and
inferred κ by up to 50%. |
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