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| Titel |
Ground-based measurements of immersion freezing in the eastern Mediterranean |
| VerfasserIn |
K. Ardon-Dryer, Z. Levin |
| 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 ; 14, no. 10 ; Nr. 14, no. 10 (2014-05-27), S.5217-5231 |
| Datensatznummer |
250118739
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| Publikation (Nr.) |
 copernicus.org/acp-14-5217-2014.pdf |
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| Zusammenfassung |
Ice nuclei were measured in immersion-freezing mode in the eastern
Mediterranean region using the FRIDGE-TAU (FRankfurt Ice-nuclei Deposition
freezinG Experiment, the Tel Aviv University version) chamber. Aerosol
particles were sampled during dust storms and on clean and polluted days
(e.g., Lag BaOmer). The aerosol immersion-freezing potential was analyzed in
the laboratory using a drop-freezing method. Droplets from all the samples
were found to freeze between −11.8 °C and −28.9 °C.
Immersion-freezing nuclei (FN) concentrations range between 0.16 L−1
and
234 L−1, while the activated fraction (AF) ranges between
8.7 × 10−8 and 4.9 × 10−4. The median temperature
at which the drops from each filter froze was found to be correlated with
the corresponding daily average of PM10, PM2.5 and
PM10–PM2.5. A higher correlation value between FN concentrations
and PM10–PM2.5 suggests that the larger particles are generally
more effective as FN.
The measurements were divided into dust storms and "clean" conditions
(this is a relative term, because dust particles are always present in the
atmosphere is this region) based on the air mass back trajectories and the
aerosol mass concentrations (PM10). Droplets containing ambient
particles from dust storm days froze at higher temperatures than droplets
containing particles from clean days. Statistically significant differences
were found between dust storms and clean conditions primarily in terms of
the initial temperature at which the first drops froze, the median freezing
temperature and the aerosol loading (PM values). FN concentrations and AF
values in dust storms were larger by more than a factor of 2 than in the
clean conditions. This observation agrees with previous studies showing that
some dust particles are almost always present in the atmosphere in this
region.
Measurements of aerosol particles emitted from wood burning bonfires during
a Lag BaOmer holiday showed that although a high concentration of particles
was emitted, those particles' effectiveness as FN was relatively poor. The most likely
reason for the low FN efficiency is the combination of relatively low fire
temperatures and high organic carbon fraction in the aerosols. |
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