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| Titel |
Size-dependent particle activation properties in fog during the ParisFog 2012/13 field campaign |
| VerfasserIn |
E. Hammer, M. Gysel, G. C. Roberts, T. Elias, J. Hofer, C. R. Hoyle, N. Bukowiecki, J.-C. Dupont, F. Burnet, U. Baltensperger, E. Weingärtner |
| 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. 19 ; Nr. 14, no. 19 (2014-10-07), S.10517-10533 |
| Datensatznummer |
250119081
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| Publikation (Nr.) |
 copernicus.org/acp-14-10517-2014.pdf |
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| Zusammenfassung |
| Fog-induced visibility reduction is responsible for a variety of hazards in
the transport sector. Therefore there is a large demand for an improved
understanding of fog formation and thus improved forecasts. Improved fog
forecasts require a better understanding of the numerous complex mechanisms
during the fog life cycle. During winter 2012/13 a field campaign called
ParisFog aiming at fog research took place at SIRTA (Instrumented
Site for Atmospheric Remote Sensing Research). SIRTA is located
about 20 km southwest of the Paris city center, France, in
a semi-urban environment. In situ activation properties of
the prevailing fog were investigated by measuring (1) total and
interstitial (non-activated) dry particle number size distributions
behind two different inlet systems; (2) interstitial hydrated
aerosol and fog droplet size distributions at ambient conditions; and
(3) cloud condensation nuclei (CCN) number concentration at
different supersaturations (SS) with a CCN counter. The aerosol
particles were characterized regarding their hygroscopic properties,
fog droplet activation behavior and contribution to light scattering
for 17 developed fog events. Low particle hygroscopicity with an
overall median of the hygroscopicity parameter, κ, of 0.14 was
found, likely caused by substantial influence from local traffic and
wood burning emissions. Measurements of the aerosol size
distribution at ambient RH revealed that the critical wet diameter,
above which the hydrated aerosols activate to fog droplets, is
rather large (with a median value of 2.6μm) and is highly
variable (ranging from 1 to 5μm) between the different
fog events. Thus, the number of activated fog droplets was very
small and the non-activated hydrated particles were found to
contribute significantly to the observed light scattering and thus
to the reduction in visibility. Combining all experimental data, the
effective peak supersaturation, SSpeak, a measure
of the peak supersaturation during the fog formation, was
determined. The median SSpeak value was estimated
to be in the range from 0.031 to 0.046% (upper and lower
limit estimations), which is in good agreement with previous
experimental and modeling studies of fog. |
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