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| Titel |
Hygroscopic mixing state of urban aerosol derived from size-resolved cloud condensation nuclei measurements during the MEGAPOLI campaign in Paris |
| VerfasserIn |
Z. Jurányi, T. Tritscher, M. Gysel, M. Laborde, L. Gomes, G. Roberts, 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 ; 13, no. 13 ; Nr. 13, no. 13 (2013-07-08), S.6431-6446 |
| Datensatznummer |
250018744
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| Publikation (Nr.) |
 copernicus.org/acp-13-6431-2013.pdf |
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| Zusammenfassung |
Ambient aerosols are a complex mixture of particles with different physical
and chemical properties and consequently distinct hygroscopic behaviour. The
hygroscopicity of a particle determines its water uptake at subsaturated
relative humidity (RH) and its ability to form a cloud droplet at
supersaturated RH. These processes influence Earth's climate and the
atmospheric lifetime of the particles.
Cloud condensation nuclei (CCN) number size distributions (i.e. CCN number
concentrations as a function of dry particle diameter) were measured close to
Paris during the MEGAPOLI campaign in January–February 2010, covering 10
different supersaturations (SS = 0.1–1.0%). The time-resolved
hygroscopic mixing state with respect to CCN activation was also derived from
these measurements. Simultaneously, a hygroscopicity tandem differential
mobility analyser (HTDMA) was used to measure the hygroscopic growth factor
(ratio of wet to dry mobility diameter) distributions at
RH = 90%. The aerosol was highly externally mixed and its
mixing state showed significant temporal variability. The average particle
hygroscopicity was relatively low at subsaturation (RH = 90%; mean hygroscopicity parameter κ = 0.12–0.27) and increased with
increasing dry diameter in the range 35–265 nm. The mean κ
value, derived from the CCN measurements at supersaturation, ranged from 0.08
to 0.24 at SS = 1.0–0.1%.
Two types of mixing-state resolved hygroscopicity closure studies were
performed, comparing the water uptake ability measured below and above
saturation. In the first type the CCN counter was connected in series with the HTDMA and and
closure was achieved over the whole range of probed dry diameters, growth
factors and supersaturations using the κ-parametrization for the water
activity and assuming surface tension of pure water in the Köhler theory.
In the second closure type we compared hygroscopicity distributions derived
from parallel monodisperse CCN measurements and HTDMA measurements. Very good
agreement was found at all supersaturations, which shows that monodisperse CCN
measurements are a reliable alternative to determine the hygroscopic mixing
state of ambient aerosols. |
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