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| Titel |
Influences on the fraction of hydrophobic and hydrophilic black carbon in the atmosphere |
| VerfasserIn |
G. R. McMeeking, N. Good, M. D. Petters, G. McFiggans, H. Coe |
| 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. 10 ; Nr. 11, no. 10 (2011-05-31), S.5099-5112 |
| Datensatznummer |
250009773
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| Publikation (Nr.) |
 copernicus.org/acp-11-5099-2011.pdf |
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| Zusammenfassung |
| Black carbon (BC) is a short term climate forcer that directly warms the
atmosphere, slows convection, and hinders quantification of the effect of
greenhouse gases on climate change. The atmospheric lifetime of BC particles
with respect to nucleation scavenging in clouds is controlled by their
ability to serve as cloud condensation nuclei (CCN). To serve as CCN under typical conditions, hydrophobic
BC particles must acquire hygroscopic
coatings. However, the quantitative relationship between coatings and
hygroscopic properties for ambient BC particles is not known nor is the time
scale for hydrophobic-to-hydrophilic conversion. Here we introduce a method
for measuring the hygroscopicity of externally and internally mixed BC
particles by coupling a single particle soot photometer with a humidified
tandem differential mobility analyzer. We test this technique using uncoated
and coated laboratory generated model BC compounds and apply it to
characterize the hygroscopicity distribution of ambient BC particles. From
these data we derive that the observed number fraction of BC that is CCN
active at 0.2 % supersaturation is generally low in an urban area near
sources and that it varies with the trajectory of the airmass. We anticipate
that our method can be combined with measures of air parcel physical and
photochemical age to provide the first quantitative estimates for
characterizing hydrophobic-to-hydrophilic conversion rates in the
atmosphere. |
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