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| Titel |
Case studies of particle formation events observed in boreal forests: implications for nucleation mechanisms |
| VerfasserIn |
F. Yu, R. Turco |
| 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 ; 8, no. 20 ; Nr. 8, no. 20 (2008-10-22), S.6085-6102 |
| Datensatznummer |
250006415
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| Publikation (Nr.) |
 copernicus.org/acp-8-6085-2008.pdf |
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| Zusammenfassung |
| Aerosol nucleation events observed worldwide may have
significant climatic and health implications. However, the specific
nucleation mechanisms remain ambiguous. Here, we report case studies of
eight nucleation events observed during an intensive field campaign at a
boreal forest site (Hyytiälä, Finland) in spring 2005. The present
analysis is based on comprehensive kinetic simulations using an ion-mediated
nucleation (IMN) model in which the key physical and chemical parameters are
constrained by a variety of recent measurements. Out of the 22 days of the
campaign on which nucleation events were observed, eight major events were
selected for detailed analysis on the basis of indications that the observed
air masses were relatively homogeneous. In most of these cases, reasonable
agreement is found between IMN predictions and field data for a range of
variables, including critical nucleation sizes, size-dependent overcharging
ratios, and the concentrations of 1.8–3 nm stable clusters and 3–6 nm particles,
and their diurnal variations. The possible reasons leading to
substantial differences between observation and theory in some cases are
also explored. Statistically, roughly 80% of the nucleation events
recorded during the Hyytiälä campaign exhibited mean size-dependent
particle overcharging ratios within the range of, or exceeding, those
predicted by the IMN model, suggesting that ion nucleation processes were
significant during these events. The nucleation rates calculated using the
IMN modeling approach are contrasted with those predicted by other
theories/models, and key differences between the results are discussed. In
particular, it is concluded that the ion nucleation model originally
developed by Lovejoy et al. (2004) significantly under-predicts ion
nucleation rates, and cannot explain the new observations from
Hyytiälä regarding the electrical properties of nanoparticles. We
also show that, for the well documented conditions of the Hyytiälä
project, the binary and ternary homogeneous nucleation rates calculated
using the most current theories would fall well below ~10−7 cm−3 s−1,
and thus would be negligible. |
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