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| Titel |
Hygroscopic properties and mixing state of aerosol measured at the high-altitude site Puy de Dôme (1465 m a.s.l.), France |
| VerfasserIn |
H. Holmgren, K. Sellegri, M. Hervo, C. Rose, E. Freney, P. Villani, P. Laj |
| 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. 18 ; Nr. 14, no. 18 (2014-09-16), S.9537-9554 |
| Datensatznummer |
250119026
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| Publikation (Nr.) |
 copernicus.org/acp-14-9537-2014.pdf |
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| Zusammenfassung |
A Hygroscopicity Tandem Differential Mobility Analyser (HTDMA) was used to
evaluate the hygroscopic properties of aerosol particles measured at the Puy
de Dôme research station in central France, periodically from September
2008 to January 2010, and almost continuously from October 2010 to December
2012. This high-altitude site is ideally situated to allow for both the
upper part of the planetary boundary layer and the lower free troposphere to
be sampled. The aim of the study is to investigate both the influence of
year-to-year, seasonal and diurnal cycles, as well as the influence of air
mass type on particle hygroscopicity and mixing state.
Results show that particle hygroscopicity increases with particle size and
depends both on air mass type and on season. Average growth factor values,
GFs, are lowest in winter (1.21 ± 0.13, 1.23 ± 0.18 and
1.38 ± 0.25 for 25, 50 and 165 nm particles, respectively) and highest
in autumn (1.27 ± 0.11, 1.32 ± 0.12 and 1.49 ± 0.15 for 25,
50 and 165 nm particles, respectively). Particles are generally more
hygroscopic at night than during the day. The seasonal and diurnal variations
are likely to be strongly influenced by boundary layer dynamics. Furthermore,
particles originating from oceanic and continental regions tend to be more
hygroscopic than those measured in African and local air masses. The high
hygroscopicity of oceanic aerosol can be explained by large proportions of
inorganic aerosol and sea salts.
Aerosols measured at the Puy de Dôme display a high degree of external
mixing, and hygroscopic growth spectra can be divided into three different
hygroscopic modes: a less-hygroscopic mode (GF < 1.3), a
hygroscopic mode (GF~1.3–1.7) and a more-hygroscopic mode
(GF > 1.7). The majority of particles measured can be classified
as being in either the less-hygroscopic mode or the hygroscopic mode, and
only few of them have more-hygroscopic properties. The degree of external
mixing, evaluated as the fraction of time when the aerosol is found with two
or more aerosol populations with different hygroscopic properties, increases
with particle size (average yearly values are 20, 28 and 45 {%} for 25, 50,
and 165 nm particles, respectively). The degree of external mixing is more
sensitive to season than to air mass type, and it is higher in the cold
seasons than in the warm seasons.
With more than two years of nearly continuous measurements, this study
gathers the results from one of the longest data sets of hygroscopic growth
factor measurements to date, allowing a statistically relevant hygroscopic
growth parameterization to be determined as a function of both air mass type
and season. |
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