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| Titel |
Insights into the role of soot aerosols in cirrus cloud formation |
| VerfasserIn |
B. Kärcher, O. Möhler, P. J. DeMott, S. Pechtl, F. Yu |
| 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 ; 7, no. 16 ; Nr. 7, no. 16 (2007-08-17), S.4203-4227 |
| Datensatznummer |
250005163
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| Publikation (Nr.) |
 copernicus.org/acp-7-4203-2007.pdf |
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| Zusammenfassung |
| Cirrus cloud formation is believed to be dominated by homogeneous freezing
of supercooled liquid aerosols in many instances. Heterogeneous ice nuclei
such as mineral dust, metallic, and soot particles, and some crystalline
solids within partially soluble aerosols are suspected to modulate cirrus
properties. Among those, the role of ubiquitous soot particles is perhaps
the least understood. Because aviation is a major source of upper
tropospheric soot particles, we put emphasis on ice formation in dispersing
aircraft plumes. The effect of aircraft soot on cirrus formation in the
absence of contrails is highly complex and depends on a wide array of
emission and environmental parameters. We use a microphysical-chemical model
predicting the formation of internally mixed, soot-containing particles up to
two days after emission, and suggest two principal scenarios: high
concentrations of original soot emissions could slightly increase the number
of ice crystals; low concentrations of particles originating from coagulation
of emitted soot with background aerosols could lead to a significant reduction
in ice crystal number. Both scenarios assume soot particles to be moderate ice
nuclei relative to cirrus formation by homogeneous freezing in the presence of
few efficient dust ice nuclei. A critical discussion of laboratory experiments
reveals that the ice nucleation efficiency of soot particles depends strongly
on their source, and, by inference, on atmospheric aging processes. Mass and
chemistry of soluble surface coatings appear to be crucial factors. Immersed
soot particles tend to be poor ice nuclei, some bare ones nucleate ice at low
supersaturations. However, a fundamental understanding of these studies is
lacking, rendering extrapolations to atmospheric conditions speculative. In
particular, we cannot yet decide which indirect aircraft effect scenario is
more plausible, and options suggested to mitigate the problem remain uncertain. |
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